Fig. 4A shows that when one compares various common single-crystal detection media and the lead chalcogenides under study, PbSe and PbTe in both single-crystal and nanocrystalline form are superior in terms of their combined mass densities and atomic numbers, Z, both of which combine to yield a higher specific detection efficiency.

The nanocrystalline forms of PbSe and PbTe are consistent with some of our current colloidal solids, in which spherical 10 nm PbSe nanoparticles or spherical 5 nm PbTe dots are spun cast into a face-centered-cubic (FCC) nanocrystalline solid with an interstitial para-MEH-PPV polymer of order 1. In realized detectors, we vary the relative blending of the

Nanoscale Methods to Enhance the Detection of Ionizing Radiation 565

As an example, Fig. 4B shows the photonic mean free path, as derived from the density and the macroscopic *photoelectric-absorption* linear attenuation coefficient at a photon energy of 662 keV, which is consistent with the gamma-ray emission from 137Cs. A comparison of PbSe or PbTe with CZT- the most common room-temperature gamma-ray detection mediumshows that the mean free path in CZT is 1.85 times longer than that of either lead salt. On a path-length normalized basis therefore, the lead chalcogenides can form a highly efficient gamma-ray detection medium. Nevertheless, the question is: in a field in which device thicknesses are measured in nanometers to hundreds of nanometers, can the solid be formed into electronic structures with enough active thickness and lateral extent to take advantage of the inherently high interaction probabilities and stop charged particles that may range over hundred of micrometers? As described in Section 2.41, the drop-, dip- and spun-cast solids can be formed into thicknesses which yield highly efficient detector configurations. One not only desires high probabilities of interaction with the incident quanta, but the multiplicity of the subsequent charge-creation should be maximized and the trapping of the charge-ensemble should be minimized so that the information conversion is optimized. As summarized in Section 2.42, the charge transport can vary across the lateral area as well as in depth because of the varying field or mobilities that accompany different packing regions. Nevertheless, one can bias the detector such that the charge velocities are saturated,

As shown in Section 2.43, even with a colloidal solid that is not optimized from a chargeseparation and transport perspective, the resulting energy-resolving behavior is comparable to or better than state-of-the-art single-crystal semiconductors- Si, CZT, and high-purity germanium operated at liquid nitrogen temperatures- which reflects the promise of the nanostructured approach to semiconductor device design, extending beyond the sensing

The chemical recipe used to form the colloidal dispersion, the subsequent characterization of the nanoparticles, and their formation into solid assemblies is described in (Kim & Hammig, 2009). Colloidal PbSe NCs were synthesized through the high-temperature solution-phase routes (Murray et al., 2001), as illustrated in the Fig. 5. Lead oleate and selenide-dissolved trioctylphosphine (TOP-Se) were used as the organo-metallic precursor and diphenyl ether (DPE) as the high-temperature organic solvent. The lead oleate precursor was prepared by dissolving lead acetate, Pb(CH3COO)2, into a mixture of DPE, TOP and oleic acid, heated up to 85 C for 1 hour and cooled down. Mixed with 1 M TOP-Se solution, precursors were rapidly injected into rigorously stirred DPE at various reaction conditions (Tinj) in an inert

In the fabrication of the NC assembly detector, one forms a mold in an inert substrate which acts as a basin into which the colloidal dispersion is dripped. Furthermore, both the top and bottom metal contacts must be accessible in order to connect each face of the detector to the readout electronics. Although we have used silicon, printed circuit board, glass, and plastic substrates, we typically use glass substrates for thin detectors (10's of micrometers to 100's of micrometers) and employ plastic substrates for millimeter or centimeter thick devices. Fig. 6 shows the typical process if a glass substrate is used, which makes use of standard

environment. PbSe NCs were grown in Tgr for 3 - 6 minutes and cooled.

resulting in uniform collection across the ensemble.

**2.4 Lead selenide NC detector responses**

application reported.

**2.4.1 Detector fabrication**

photolithography processes.

polymer and NCs such that higher polymer orders are typically employed, and we grow rods and cubes, as well as spheres. Furthermore, the geometry of the solid deviates from a perfect FCC structure to a degree depending on the size dispersion of the colloidal solution; nevertheless, the reduction in densities between the single-crystal lead chalcogenides and the nanocrystalline forms reflects the values that are achieved when the ordering and spacing are optimized for spherical NCs. As shown in the figure, even in nanocrystalline form, the lead chalcogenides maximize the probability of interacting with impinging highenergy photons, and more generally, they exhibit superior characteristics for the efficient stopping of primary or secondary charged particles.

Fig. 4. (A) Relationship between the average atomic number *Z* and the mass density for various semiconducting materials. (B) The mean free path for a 662 keV photon interacting with single-crystal forms of the semiconducting media (Hammig & Kim, 2011).

polymer and NCs such that higher polymer orders are typically employed, and we grow rods and cubes, as well as spheres. Furthermore, the geometry of the solid deviates from a perfect FCC structure to a degree depending on the size dispersion of the colloidal solution; nevertheless, the reduction in densities between the single-crystal lead chalcogenides and the nanocrystalline forms reflects the values that are achieved when the ordering and spacing are optimized for spherical NCs. As shown in the figure, even in nanocrystalline form, the lead chalcogenides maximize the probability of interacting with impinging highenergy photons, and more generally, they exhibit superior characteristics for the efficient

Fig. 4. (A) Relationship between the average atomic number *Z* and the mass density for various semiconducting materials. (B) The mean free path for a 662 keV photon interacting

**B**

**A**

with single-crystal forms of the semiconducting media (Hammig & Kim, 2011).

stopping of primary or secondary charged particles.

As an example, Fig. 4B shows the photonic mean free path, as derived from the density and the macroscopic *photoelectric-absorption* linear attenuation coefficient at a photon energy of 662 keV, which is consistent with the gamma-ray emission from 137Cs. A comparison of PbSe or PbTe with CZT- the most common room-temperature gamma-ray detection mediumshows that the mean free path in CZT is 1.85 times longer than that of either lead salt. On a path-length normalized basis therefore, the lead chalcogenides can form a highly efficient gamma-ray detection medium. Nevertheless, the question is: in a field in which device thicknesses are measured in nanometers to hundreds of nanometers, can the solid be formed into electronic structures with enough active thickness and lateral extent to take advantage of the inherently high interaction probabilities and stop charged particles that may range over hundred of micrometers? As described in Section 2.41, the drop-, dip- and spun-cast solids can be formed into thicknesses which yield highly efficient detector configurations.

One not only desires high probabilities of interaction with the incident quanta, but the multiplicity of the subsequent charge-creation should be maximized and the trapping of the charge-ensemble should be minimized so that the information conversion is optimized. As summarized in Section 2.42, the charge transport can vary across the lateral area as well as in depth because of the varying field or mobilities that accompany different packing regions. Nevertheless, one can bias the detector such that the charge velocities are saturated, resulting in uniform collection across the ensemble.

As shown in Section 2.43, even with a colloidal solid that is not optimized from a chargeseparation and transport perspective, the resulting energy-resolving behavior is comparable to or better than state-of-the-art single-crystal semiconductors- Si, CZT, and high-purity germanium operated at liquid nitrogen temperatures- which reflects the promise of the nanostructured approach to semiconductor device design, extending beyond the sensing application reported.

#### **2.4 Lead selenide NC detector responses 2.4.1 Detector fabrication**

The chemical recipe used to form the colloidal dispersion, the subsequent characterization of the nanoparticles, and their formation into solid assemblies is described in (Kim & Hammig, 2009). Colloidal PbSe NCs were synthesized through the high-temperature solution-phase routes (Murray et al., 2001), as illustrated in the Fig. 5. Lead oleate and selenide-dissolved trioctylphosphine (TOP-Se) were used as the organo-metallic precursor and diphenyl ether (DPE) as the high-temperature organic solvent. The lead oleate precursor was prepared by dissolving lead acetate, Pb(CH3COO)2, into a mixture of DPE, TOP and oleic acid, heated up to 85 C for 1 hour and cooled down. Mixed with 1 M TOP-Se solution, precursors were rapidly injected into rigorously stirred DPE at various reaction conditions (Tinj) in an inert environment. PbSe NCs were grown in Tgr for 3 - 6 minutes and cooled.

In the fabrication of the NC assembly detector, one forms a mold in an inert substrate which acts as a basin into which the colloidal dispersion is dripped. Furthermore, both the top and bottom metal contacts must be accessible in order to connect each face of the detector to the readout electronics. Although we have used silicon, printed circuit board, glass, and plastic substrates, we typically use glass substrates for thin detectors (10's of micrometers to 100's of micrometers) and employ plastic substrates for millimeter or centimeter thick devices. Fig. 6 shows the typical process if a glass substrate is used, which makes use of standard photolithography processes.

Nanoscale Methods to Enhance the Detection of Ionizing Radiation 567

Fig. 6. Schematic of glass wafer-based NC assembly substrate fabrication procedure.

Fig. 7. Glass wafer-based NC assembly substrate with Al and Au bottom contacts.

allows more uniform spreading of the NC solution as well as more rapid drying.

Synthesized NC particles inherently self-assemble, if coordinated with organic ligands properly. NC particles dispersed in the chloroform solvent can be deposited on the substrate using many methods, but we have focused on drop- and spin-casting. Drop-casting is the process of depositing a droplet of the NC solution on the substrate and repeating the procedure, while allowing time for the solvent to evaporate between applications. Spincasting is the process of dripping a droplet of the solution on a spinning substrate, which

Fig. 5. Schematic of the PbSe NC dispersion synthesis.

Several fabricated substrates are shown in the Fig. 7. The lines stretching horizontally and vertically are due to the dicing of the substrate. Blue colored tape is attached to the backside, before the substrate is diced. The glass wafer-based substrates were designed in a circular shape to make the spin-casting procedure more efficient. Once the metalized molds are realized, the NC assembly can be deposited to form the active region of the sensor.

Fig. 5. Schematic of the PbSe NC dispersion synthesis.

Several fabricated substrates are shown in the Fig. 7. The lines stretching horizontally and vertically are due to the dicing of the substrate. Blue colored tape is attached to the backside, before the substrate is diced. The glass wafer-based substrates were designed in a circular shape to make the spin-casting procedure more efficient. Once the metalized molds are

realized, the NC assembly can be deposited to form the active region of the sensor.

Fig. 6. Schematic of glass wafer-based NC assembly substrate fabrication procedure.

Fig. 7. Glass wafer-based NC assembly substrate with Al and Au bottom contacts.

Synthesized NC particles inherently self-assemble, if coordinated with organic ligands properly. NC particles dispersed in the chloroform solvent can be deposited on the substrate using many methods, but we have focused on drop- and spin-casting. Drop-casting is the process of depositing a droplet of the NC solution on the substrate and repeating the procedure, while allowing time for the solvent to evaporate between applications. Spincasting is the process of dripping a droplet of the solution on a spinning substrate, which allows more uniform spreading of the NC solution as well as more rapid drying.

Nanoscale Methods to Enhance the Detection of Ionizing Radiation 569

As mentioned in Section 2.2, a close-packed solid with a high degree of size uniformity results in high conductivity. The size-dispersion in the NC solution depends on procedures used to prepare the liquid dispersion of coordinated-NCs. One can achieve monodisperse (particle size with less than 5 % uncertainty) solutions either directly from the nucleation and growth procedure- with finely controlled reaction conditions- or by employing sizeselective precipitation procedures. For instance, Fig. 10 shows the size separation for CdTe NCs that can be elicited using incompatible and compatible solvents along with centrifugation, into a size-stratified solution (Fig. 10A). The separated layers (Fig. 10B) then exhibit different particle size via their size-dependent band-gap in their color or in their excitation spectra. The size can be further refined by repeated application of the procedures

Fig. 10. (A) The separation of a CdTe NC dispersion (with size range in the 3-5 nm range) into different precipitation bands following centrifugation. (B) The separation of the bands

**A B**

The importance of monodispersity is not only in the electrical characteristics but in the mechanical ordering properties (Coe-Sullivan et al., 2005). A large (> 10 %) distribution in size results in random packing, but narrow distributions that approach the uncertainty due

Over microscopic areas therefore, monodispersity and the coordination chemistry can be employed to realize close-packed assemblies. However, when one examines the solid over larger volumes, then defects are apparent, ranging from quantum dot (QD) crystal defects, such as vacancies and dislocations, to large-scale cracks, such as those shown in Fig. 11. The large-scale cracking, which we see in all of our samples is a natural consequence of stressrelief during drying of the solvent. The formation of domains of differing degrees of NC

For instance, if the bias if held low enough (a value depending on the diode design), then Fig. 12 shows that following the interaction of a single quanta, the holes move in fits and starts, as reflected in the induced charge pulses (in yellow) along with their amplified and shaped counterparts (in blue). This reflects an underlying variation in the drift velocity as the charge cloud traverses different depths of the active volume, with can be caused by either variations in the electric field or the mobility. Although these variations could

to the addition of an atomic layer (< 5 %) result in high degrees of order.

order can be reflected in the charge transport characteristics.

**2.4.2 Charge transport characteristics**

into different vials through pipetting.

if needed.

In order to realize suitable charge transport, the PbSe NC solution is mixed with a conductive polymer, for instance, para-MEH-PPV, which is used as a hole transporting agent. Greater polymer concentrations formed a brighter, more yellow assembly, whereas the pure PbSe NC assembly exhibits a dark assembly, as shown in Fig. 8 and Fig. 9. Note that Fig. 9 shows the assemblies deposited into ~5 mm deep holes with 7 mm diameters milled into plastic substrates, and the detectors therefore form active depths that are several millimeters thick.

Fig. 8. PbSe NC/MEH-PPH composite assembly deposited on the glass substrate.

Fig. 9. PbSe NC/MEH-PPH composite assembly deposited on plastic substrates, before the top metal contact is formed (left) and after gold evaporation (right).

Various metal contacts can be used to abut the NC assembly, in which the band-structure can vary significantly with the particle size. In general, the MEH-PPV is p-type and we therefore use metal contacts with higher work functions, such as Pt (5.6 eV) and Au (5.2 eV), for the ohmic contact, and we form the rectifying contact with lower work function metals, such as In (3.8 eV) and Al (4.2 eV). Various combinations of samples were made in order to study the effects of the metal contacts, including Pt/NC/Pt, Pt/NC/In, Au/NC/Au, Au/NC/In, etc.. Nevertheless, the behavior of the resulting detector does not depend strongly on the bounding Schottky barrier; rather, the charge creation and transport is more dependent on the uniformity of the colloidal solid underlying the electrodes, some features of which will be described next.

## **2.4.2 Charge transport characteristics**

568 Current Topics in Ionizing Radiation Research

In order to realize suitable charge transport, the PbSe NC solution is mixed with a conductive polymer, for instance, para-MEH-PPV, which is used as a hole transporting agent. Greater polymer concentrations formed a brighter, more yellow assembly, whereas the pure PbSe NC assembly exhibits a dark assembly, as shown in Fig. 8 and Fig. 9. Note that Fig. 9 shows the assemblies deposited into ~5 mm deep holes with 7 mm diameters milled into plastic substrates, and the detectors therefore form active depths that are several

Fig. 8. PbSe NC/MEH-PPH composite assembly deposited on the glass substrate.

Fig. 9. PbSe NC/MEH-PPH composite assembly deposited on plastic substrates, before the

Various metal contacts can be used to abut the NC assembly, in which the band-structure can vary significantly with the particle size. In general, the MEH-PPV is p-type and we therefore use metal contacts with higher work functions, such as Pt (5.6 eV) and Au (5.2 eV), for the ohmic contact, and we form the rectifying contact with lower work function metals, such as In (3.8 eV) and Al (4.2 eV). Various combinations of samples were made in order to study the effects of the metal contacts, including Pt/NC/Pt, Pt/NC/In, Au/NC/Au, Au/NC/In, etc.. Nevertheless, the behavior of the resulting detector does not depend strongly on the bounding Schottky barrier; rather, the charge creation and transport is more dependent on the uniformity of the colloidal solid underlying the electrodes, some features

top metal contact is formed (left) and after gold evaporation (right).

of which will be described next.

millimeters thick.

As mentioned in Section 2.2, a close-packed solid with a high degree of size uniformity results in high conductivity. The size-dispersion in the NC solution depends on procedures used to prepare the liquid dispersion of coordinated-NCs. One can achieve monodisperse (particle size with less than 5 % uncertainty) solutions either directly from the nucleation and growth procedure- with finely controlled reaction conditions- or by employing sizeselective precipitation procedures. For instance, Fig. 10 shows the size separation for CdTe NCs that can be elicited using incompatible and compatible solvents along with centrifugation, into a size-stratified solution (Fig. 10A). The separated layers (Fig. 10B) then exhibit different particle size via their size-dependent band-gap in their color or in their excitation spectra. The size can be further refined by repeated application of the procedures if needed.

Fig. 10. (A) The separation of a CdTe NC dispersion (with size range in the 3-5 nm range) into different precipitation bands following centrifugation. (B) The separation of the bands into different vials through pipetting.

The importance of monodispersity is not only in the electrical characteristics but in the mechanical ordering properties (Coe-Sullivan et al., 2005). A large (> 10 %) distribution in size results in random packing, but narrow distributions that approach the uncertainty due to the addition of an atomic layer (< 5 %) result in high degrees of order.

Over microscopic areas therefore, monodispersity and the coordination chemistry can be employed to realize close-packed assemblies. However, when one examines the solid over larger volumes, then defects are apparent, ranging from quantum dot (QD) crystal defects, such as vacancies and dislocations, to large-scale cracks, such as those shown in Fig. 11. The large-scale cracking, which we see in all of our samples is a natural consequence of stressrelief during drying of the solvent. The formation of domains of differing degrees of NC order can be reflected in the charge transport characteristics.

For instance, if the bias if held low enough (a value depending on the diode design), then Fig. 12 shows that following the interaction of a single quanta, the holes move in fits and starts, as reflected in the induced charge pulses (in yellow) along with their amplified and shaped counterparts (in blue). This reflects an underlying variation in the drift velocity as the charge cloud traverses different depths of the active volume, with can be caused by either variations in the electric field or the mobility. Although these variations could

Nanoscale Methods to Enhance the Detection of Ionizing Radiation 571

Fig. 13. The pulse shape derived from the charge-sensitive preamplifier (Ortec 142a) when an alpha particle from 241Am is impinged upon a silicon PIN or NC PbSe detector, both operated at 0 V applied bias. The PbSe nanoparticles are spherical with a mean diameter of

Thus, although the dispersion in not monodisperse and the solid is not uniform, the promise of the nanocrystalline approach is revealed in the fact that the results are comparable to or

Fig. 14A corresponds to a mixed spectrum derived from alpha particles- emerging from a *thin-film* 241Am alpha particle source and 133Ba gamma-rays impinging upon the 1 x 1 cm detector shown in Fig. 14A. The alpha source, placed 3.7 cm away from the detector surface, attenuates the 5.49 MeV particles to the energy range shown, and the 133Ba source was placed external to the box housing the detector, 5 cm distant. If one focuses on those spectral features whose appearance correlates to the presence of the 133Ba source, then we can identify the features using both the pulse amplitude and the frequency of occurrence as

Although the material need not be linear, the pulse amplitudes of the full-energy gammaray peaks were linearly related to the energies identified in Fig. 14B. Second, the areas under the spectral features correspond to the expected values. For instance, if one takes the gamma-ray emission yield as well as the photoelectric absorption probabilities into account, the area of the 383.85 keV peak should be 12 % of that under the 356.02 keV peak, compared with a measured value of 11 %. The sizes of the x-ray escape features diminish for thicker detectors; however, the thin detector was utilized to characterize the charge-creation characteristics, minimally adulterated by charge-loss considerations, so that the inherent

better than state-of-the art single crystal detectors, as will be shown next.

7.4 nm (+ 0.5 nm).

follows.

**2.4.3 Spectroscopic measurements**

physical properties could be better estimated.

potentially be problematic if one were to use pulses such as those shown in Fig. 12 to extract the energy deposited by the radiation, one can increase the voltage such that all of the slowdrift regions are eliminated, and the pulse rises sharply and cleanly, such as that shown in Fig. 13. One explanation for this behavior is that the charge-velocities saturate across the various domains in the NC detector and the transport variations are therefore of no consequence.

Fig. 11. The cracked and stacked dried mud-puddle look of the NC assembly at a scale of 10's of micrometers.

Fig. 12. Two examples of preamp (yellow) and shaped (blue) signals derived following the stopping of an 241Am alpha particle within an under-based colloidal PbSe detector.

potentially be problematic if one were to use pulses such as those shown in Fig. 12 to extract the energy deposited by the radiation, one can increase the voltage such that all of the slowdrift regions are eliminated, and the pulse rises sharply and cleanly, such as that shown in Fig. 13. One explanation for this behavior is that the charge-velocities saturate across the various domains in the NC detector and the transport variations are therefore of no

Fig. 11. The cracked and stacked dried mud-puddle look of the NC assembly at a scale of

Fig. 12. Two examples of preamp (yellow) and shaped (blue) signals derived following the

stopping of an 241Am alpha particle within an under-based colloidal PbSe detector.

consequence.

10's of micrometers.

Fig. 13. The pulse shape derived from the charge-sensitive preamplifier (Ortec 142a) when an alpha particle from 241Am is impinged upon a silicon PIN or NC PbSe detector, both operated at 0 V applied bias. The PbSe nanoparticles are spherical with a mean diameter of 7.4 nm (+ 0.5 nm).

Thus, although the dispersion in not monodisperse and the solid is not uniform, the promise of the nanocrystalline approach is revealed in the fact that the results are comparable to or better than state-of-the art single crystal detectors, as will be shown next.

#### **2.4.3 Spectroscopic measurements**

Fig. 14A corresponds to a mixed spectrum derived from alpha particles- emerging from a *thin-film* 241Am alpha particle source and 133Ba gamma-rays impinging upon the 1 x 1 cm detector shown in Fig. 14A. The alpha source, placed 3.7 cm away from the detector surface, attenuates the 5.49 MeV particles to the energy range shown, and the 133Ba source was placed external to the box housing the detector, 5 cm distant. If one focuses on those spectral features whose appearance correlates to the presence of the 133Ba source, then we can identify the features using both the pulse amplitude and the frequency of occurrence as follows.

Although the material need not be linear, the pulse amplitudes of the full-energy gammaray peaks were linearly related to the energies identified in Fig. 14B. Second, the areas under the spectral features correspond to the expected values. For instance, if one takes the gamma-ray emission yield as well as the photoelectric absorption probabilities into account, the area of the 383.85 keV peak should be 12 % of that under the 356.02 keV peak, compared with a measured value of 11 %. The sizes of the x-ray escape features diminish for thicker detectors; however, the thin detector was utilized to characterize the charge-creation characteristics, minimally adulterated by charge-loss considerations, so that the inherent physical properties could be better estimated.

Nanoscale Methods to Enhance the Detection of Ionizing Radiation 573

Fig. 15. (A) Spectral comparison between high-resistivity silicon (green), CZT (red), HPGe (blue), and the PbSe nanocomposite (black), when exposed to gamma-rays emitted from 133Ba. The different measurement periods (e.g. 21.2 min for NC PbSe, 24 hr for HPGe) account for the differences in curve smoothness, and the curves were normalized to the number of counts in the PbSe peak. Note that the HPGe and NC PbSe traces largely overlap except for the x-ray escape peak from the NC PbSe detector. (B) Close-up of the 356.02 keV

**C**

**A B**

peak. (C) Spectral comparison between CZT (red), HPGe (blue), and the PbSe

spectrum was 46.4 min. (Hammig & Kim, 2011).

nanocomposite (black), when impinged upon by gamma-rays emitted from 137Cs. The energy resolutions are shown in the legend. The measurement period for the NC PbSe

As shown in Figs. 15A and 15B, the energy resolution of the PbSe nanocomposite is superior to silicon and CZT and comparable to HPGe, yielding an energy resolution of 0.42 % (1.5 keV) at 356 keV, compared with a resolution of 0.96 % (3.4 keV) for CZT and 0.39 % (1.4 keV) for HPGe. Fig. 15C shows an equivalent comparison between the detectors when impinged upon by 661.7 keV gamma-rays from 137Cs. The 137Cs source was more than one hundred times less intense than the 133Ba source and the peak was therefore less well sampled. More importantly, a slight gain drift in the detector dominated the peak width shown in the figure. Nevertheless, the 137Cs results buttress those derived from 133Ba

Fig. 14. (A) Energy spectrum derived from 133Ba gamma-rays and 241Am alpha particles, attenuated through 3.7 cm of air, impinging upon a 1 x 1 cm thin (10's of micrometers) composite assembly of para-MEH-PPV and star-shaped PbSe nanopartiles, accumulated for various durations shown in the legend. The inset shows a TEM micrograph of a typical PbSe NC in the assembly. (B) Typical 133Ba spectrum derived from a thin detector, in which the Pb and Se x-ray escape peaks are prominent.

As reported in (Hammig & Kim, 2011), Fig. 15 shows the spectral widths compared with three state-of-art detectors, all operated at room temperature except for the high purity germanium (HPGe) detector, which was cooled with liquid nitrogen.

**A**

**B**

Fig. 14. (A) Energy spectrum derived from 133Ba gamma-rays and 241Am alpha particles, attenuated through 3.7 cm of air, impinging upon a 1 x 1 cm thin (10's of micrometers) composite assembly of para-MEH-PPV and star-shaped PbSe nanopartiles, accumulated for various durations shown in the legend. The inset shows a TEM micrograph of a typical PbSe NC in the assembly. (B) Typical 133Ba spectrum derived from a thin detector, in which the Pb

As reported in (Hammig & Kim, 2011), Fig. 15 shows the spectral widths compared with three state-of-art detectors, all operated at room temperature except for the high purity

germanium (HPGe) detector, which was cooled with liquid nitrogen.

and Se x-ray escape peaks are prominent.

Fig. 15. (A) Spectral comparison between high-resistivity silicon (green), CZT (red), HPGe (blue), and the PbSe nanocomposite (black), when exposed to gamma-rays emitted from 133Ba. The different measurement periods (e.g. 21.2 min for NC PbSe, 24 hr for HPGe) account for the differences in curve smoothness, and the curves were normalized to the number of counts in the PbSe peak. Note that the HPGe and NC PbSe traces largely overlap except for the x-ray escape peak from the NC PbSe detector. (B) Close-up of the 356.02 keV peak. (C) Spectral comparison between CZT (red), HPGe (blue), and the PbSe nanocomposite (black), when impinged upon by gamma-rays emitted from 137Cs. The energy resolutions are shown in the legend. The measurement period for the NC PbSe spectrum was 46.4 min. (Hammig & Kim, 2011).

As shown in Figs. 15A and 15B, the energy resolution of the PbSe nanocomposite is superior to silicon and CZT and comparable to HPGe, yielding an energy resolution of 0.42 % (1.5 keV) at 356 keV, compared with a resolution of 0.96 % (3.4 keV) for CZT and 0.39 % (1.4 keV) for HPGe. Fig. 15C shows an equivalent comparison between the detectors when impinged upon by 661.7 keV gamma-rays from 137Cs. The 137Cs source was more than one hundred times less intense than the 133Ba source and the peak was therefore less well sampled. More importantly, a slight gain drift in the detector dominated the peak width shown in the figure. Nevertheless, the 137Cs results buttress those derived from 133Ba

Nanoscale Methods to Enhance the Detection of Ionizing Radiation 575

metamaterial, then the effective medium approximation can be extended to increasingly small wavelengths such that UV, x-ray, and potentially, gamma-ray wave-guiding can be elicited. Such a development has consequnce for not only sensing applications but it also provides an alternative radiation-shielding modality to the existing materials, and provides

There has been no *fundamental* advance in the science of nuclear-radiation shielding since the dawn of the nuclear era. Existing shielding materials depend on *particle*-interaction models, in which one maximizes the number of high cross-section scattering sites that can be placed between the radiation source and the protected asset. However, the advent of nanostructured materials provides means through which novel physics can be realized. In particular, they provide a physical pathway through which the wave mechanics of electromagnetic radiation can be controlled via the spatial mapping of the permittivity and permeability. Such control can be realized over electromagnetic waves ranging from microwaves to optical photons. Extending that capability to shorter wavelengths requires either correspondingly smaller nanostructures, or new modalities for controlling the indices

Invisibility cloaks generally operate on two operational principles. In the first, transformational optics- in which optical conformal mapping is used to design and grade a refractive index profile- can be used to render an object invisible by precisely guiding the flow of electromagnetic radiation around the object, in a push-forward mapping cloak or a conformal mapping cloak (H. Chen et al., 2010). The underlying mechanism stems from the invariance of Maxwell's equations to coordinate transformations, the effect of which is to only change constitutive parameters and field values. Thus, the space about a cloaked object

can be removed from the space that is transformed by the coordinate transformation.

If one utilizes a metamaterial with a negative index of refraction, then one can also cloak an object by cancelling the wave scattering from the target. Optical negative index metamaterials (NIMs) typically require a plasmonic material, which is comprised of a metaldielectric composite comprised of nanoscale-sized elements. For instance, Valentine et al. utilized a structure consisting of alternating layers of Ag and MgF2 in a cascaded fishnet structure, in order to realize a 3D optical metamaterial with very low losses (Valentine et al., 2011). The unit cell dimensions were 860 x 565 x 265 nm and the material successfully exhibited the desired refractive index at optical wavelengths of 1200 – 1700 nm; thus, the nanostructural dimensions were approximately one-half to one third of the wavelength. Note that the regular structure of the fishnet structure, shown in Fig. 16b, was patterned using focused ion-beam (FIB) milling, which is capable of precise, nanoscale cutting with

Another example is shown in Fig. 16a, in which an optical cloak for the transverse magnetic waveguide mode is comprised of isotropic dielectric materials and delivered broadband and low-loss invisibility in the 1400-1800 wavelength range. The hole diameter shown in Fig. 16a is 110 nm, approximately one-tenth the wavelength, and was again realized with FIB

In fact, most of the cloaking demonstrations to date have used a material-*removal* fabrication modality in which the composite structure is built-up via deposition procedures, and then electron beam lithography or FIB milling is used to realize the structure by etching the underlying composite. Unfortunately, both procedures are slow and costly when implemented over large areas. More importantly, they do not generally allow the precise patterning of materials to the levels required to realize wave optics with x- or gamma-rays.

the promise of light-weight, high efficiency shielding systems.

of refraction.

high aspect ratios.

milling.

gamma-rays; namely, the nanocomposite detector provides an energy estimate with similar fidelity to that produced by HPGe. The results imply that the conductive polymers are not only accomplishing the goal of realizing good charge transport through the device, but they are not substantially participating in the charge loss of the recoil electrons.

## **2.5 Summary**

Nanostructured cadmium and lead salts have been extensively studied as advanced media for optoelectronic devices. The sensitivity of their charge-transport properties to the surface conditioning of the nanoparticles and their degradation under ambient conditions has discouraged their use in a semiconductor configuration; rather, most of the efforts geared toward nuclear radiation detection have concentrated on nanostructured *scintillation* materials. Furthermore, the slight thicknesses that accompany the traditional spin-, dip-, and drop-casting methods have argued against their use as sensors of more highly-penetrating radiation.

However, we have shown that detectors with deep depletion regions can be constructed such that the deposited charge can be effectively drifted and the energy of the interacting quanta can therefore be measured. Furthermore, the accuracy of that measurement is comparable to those estimates provided by the best single-crystalline semiconducting materials, providing evidence for enhanced charge multiplication as the degree of strong confinement is increased.

Nevertheless, if one does employ thin detectors, then they are susceptible to the escape of the primary or secondary charged particles induced by the radiation's interaction, particularly for neutral particles that interact with roughly equal probability throughout the interaction depth of thin stopping media. The low energy tailing in the spectral features that are inherent to this energy loss can negatively impact the ability of the sensor to extract the physical characteristics of the impinging quantum, but more importantly, small volume detectors are inefficient for highly penetrating particles.

For neutral species, one might prefer to avoid the abrupt modality altogether, in which the particle is first converted into secondary charge particles which then confer the incident particle's information via electromagnetic interactions. If one can take advantage of the wave mechanics of the impinging quanta, then they can be guided into the detection volume such that the momentum and energy information is fully preserved, the potential of which is discussed in the next section.

## **3. Extending the bandwidth of wave-guiding media via self-assembled metamaterials**

If one can inject the incident particle's energy into mechanical vibrational modes, such as the lever modes discussed in (Hammig, 20005) or the whispering-gallery modes discussed in (Zehnpfennig et al., 2011), then one can eskew the charge-conversion process altogether, as well as the inefficiencies inherent to the charge creation and collection processes. Utilizing the wave-mechanics of the radiation proceeds most simply from long wavelength electromagnetic waves, where microwave and optical light guiding and cloaking have already been demonstrated, to the shorter wavelengths that accompany ionizing radiation. The science of guiding electromagnetic waves is aided by the development of metamaterials, which permit one to exercise control over the permittivity and permeability of the transmission medium. If one can reduce the sizes of the nanoscale features in a

gamma-rays; namely, the nanocomposite detector provides an energy estimate with similar fidelity to that produced by HPGe. The results imply that the conductive polymers are not only accomplishing the goal of realizing good charge transport through the device, but they

Nanostructured cadmium and lead salts have been extensively studied as advanced media for optoelectronic devices. The sensitivity of their charge-transport properties to the surface conditioning of the nanoparticles and their degradation under ambient conditions has discouraged their use in a semiconductor configuration; rather, most of the efforts geared toward nuclear radiation detection have concentrated on nanostructured *scintillation* materials. Furthermore, the slight thicknesses that accompany the traditional spin-, dip-, and drop-casting methods have argued against their use as sensors of more highly-penetrating

However, we have shown that detectors with deep depletion regions can be constructed such that the deposited charge can be effectively drifted and the energy of the interacting quanta can therefore be measured. Furthermore, the accuracy of that measurement is comparable to those estimates provided by the best single-crystalline semiconducting materials, providing evidence for enhanced charge multiplication as the degree of strong

Nevertheless, if one does employ thin detectors, then they are susceptible to the escape of the primary or secondary charged particles induced by the radiation's interaction, particularly for neutral particles that interact with roughly equal probability throughout the interaction depth of thin stopping media. The low energy tailing in the spectral features that are inherent to this energy loss can negatively impact the ability of the sensor to extract the physical characteristics of the impinging quantum, but more importantly, small volume

For neutral species, one might prefer to avoid the abrupt modality altogether, in which the particle is first converted into secondary charge particles which then confer the incident particle's information via electromagnetic interactions. If one can take advantage of the wave mechanics of the impinging quanta, then they can be guided into the detection volume such that the momentum and energy information is fully preserved, the potential of which

If one can inject the incident particle's energy into mechanical vibrational modes, such as the lever modes discussed in (Hammig, 20005) or the whispering-gallery modes discussed in (Zehnpfennig et al., 2011), then one can eskew the charge-conversion process altogether, as well as the inefficiencies inherent to the charge creation and collection processes. Utilizing the wave-mechanics of the radiation proceeds most simply from long wavelength electromagnetic waves, where microwave and optical light guiding and cloaking have already been demonstrated, to the shorter wavelengths that accompany ionizing radiation. The science of guiding electromagnetic waves is aided by the development of metamaterials, which permit one to exercise control over the permittivity and permeability of the transmission medium. If one can reduce the sizes of the nanoscale features in a

**3. Extending the bandwidth of wave-guiding media via self-assembled**

are not substantially participating in the charge loss of the recoil electrons.

**2.5 Summary**

radiation.

confinement is increased.

is discussed in the next section.

**metamaterials**

detectors are inefficient for highly penetrating particles.

metamaterial, then the effective medium approximation can be extended to increasingly small wavelengths such that UV, x-ray, and potentially, gamma-ray wave-guiding can be elicited. Such a development has consequnce for not only sensing applications but it also provides an alternative radiation-shielding modality to the existing materials, and provides the promise of light-weight, high efficiency shielding systems.

There has been no *fundamental* advance in the science of nuclear-radiation shielding since the dawn of the nuclear era. Existing shielding materials depend on *particle*-interaction models, in which one maximizes the number of high cross-section scattering sites that can be placed between the radiation source and the protected asset. However, the advent of nanostructured materials provides means through which novel physics can be realized. In particular, they provide a physical pathway through which the wave mechanics of electromagnetic radiation can be controlled via the spatial mapping of the permittivity and permeability. Such control can be realized over electromagnetic waves ranging from microwaves to optical photons. Extending that capability to shorter wavelengths requires either correspondingly smaller nanostructures, or new modalities for controlling the indices of refraction.

Invisibility cloaks generally operate on two operational principles. In the first, transformational optics- in which optical conformal mapping is used to design and grade a refractive index profile- can be used to render an object invisible by precisely guiding the flow of electromagnetic radiation around the object, in a push-forward mapping cloak or a conformal mapping cloak (H. Chen et al., 2010). The underlying mechanism stems from the invariance of Maxwell's equations to coordinate transformations, the effect of which is to only change constitutive parameters and field values. Thus, the space about a cloaked object can be removed from the space that is transformed by the coordinate transformation.

If one utilizes a metamaterial with a negative index of refraction, then one can also cloak an object by cancelling the wave scattering from the target. Optical negative index metamaterials (NIMs) typically require a plasmonic material, which is comprised of a metaldielectric composite comprised of nanoscale-sized elements. For instance, Valentine et al. utilized a structure consisting of alternating layers of Ag and MgF2 in a cascaded fishnet structure, in order to realize a 3D optical metamaterial with very low losses (Valentine et al., 2011). The unit cell dimensions were 860 x 565 x 265 nm and the material successfully exhibited the desired refractive index at optical wavelengths of 1200 – 1700 nm; thus, the nanostructural dimensions were approximately one-half to one third of the wavelength. Note that the regular structure of the fishnet structure, shown in Fig. 16b, was patterned using focused ion-beam (FIB) milling, which is capable of precise, nanoscale cutting with high aspect ratios.

Another example is shown in Fig. 16a, in which an optical cloak for the transverse magnetic waveguide mode is comprised of isotropic dielectric materials and delivered broadband and low-loss invisibility in the 1400-1800 wavelength range. The hole diameter shown in Fig. 16a is 110 nm, approximately one-tenth the wavelength, and was again realized with FIB milling.

In fact, most of the cloaking demonstrations to date have used a material-*removal* fabrication modality in which the composite structure is built-up via deposition procedures, and then electron beam lithography or FIB milling is used to realize the structure by etching the underlying composite. Unfortunately, both procedures are slow and costly when implemented over large areas. More importantly, they do not generally allow the precise patterning of materials to the levels required to realize wave optics with x- or gamma-rays.

Nanoscale Methods to Enhance the Detection of Ionizing Radiation 577

combination of sol preparation and electrophoretic deposition has been used to synthesize a variety of oxide nanorod arrays, such as TiO2, SiO2, Nb2O5, V2O5, BaTiO3, Pb(Zr,Ti)O3, Sndoped In2O3 (ITO), and Sr2Nb2O7 (Kao, 2004). We have grown nanowires from CdTe and PbSe semiconductors, upon which metallic shells can be deposited. There has been a myriad of different self-assembled nanostructures, but they do not approach the process uniformity and control that accompanies batch-processing methods (cf. Ko et al., 2011) , and the deviations in the uniformity would diminish any wave-guiding achieved from a designed array of plasmonic structures of similar size. Nevertheless, some wave guiding can occur from an array of proper materials. Thus, using fabrication techniques similar to that that have been successfully employed to make high-performance charge-conversion devices, one can conceivably change the materials in the nanostructured array in order to excercise

Nanostructured media allow us to measure ionizing radiation with greater precision than can be achieved with single-crystal media because one has greater experimental control over the detector's governing parameters- the size and shape of the nanoparticles- than can be equivalently achieved in a nominally single-crystal media, in which defects and impurities can readily spoil the performance of the sensor. More importantly, one can yield fundamentally superior detection characteristics because one has a mechanism through which the informational processes- such as electron creation- can be controlled relative to the loss processes- such as phonon excitation. Fortuitously, this superior physics is also

Nanostructured materials have therefore been projected as the next-generation material for the detection of ionizing radiation, the adoption of which depends on overcoming the expected difficulties associated with using a composite material comprised of innumerable interfaces at which information can be lost. As we have shown in this chapter, methods exist that can quench interface trapping so that the promise of the material can be realized today.

Bahl, G.; et al., Stimulated optomechanical excitation of surface acoustic waves in a

Chen, H.; C. Chan & P. Sheng. Transformation optics and metamaterials, *Nature Materials*

Coe-Sullivan, S.; et al., "Large-Area Ordered Quantum-Dot Monolayers via Phase

Du, H.; et al., Optical properties of colloidal PbSe nanocrystals, *Nano Lett.*, vol. 2, no. 11, pp.

Hammig, M.D; D. K. Wehe and J. A. Nees, , The measurement of sub-brownian lever

Hammig, M.D.; G. Kim, Fine Spectroscopy of Ionizing Radiation via a Colloidal Array of

Jacobsohn, L.G.; et al., Fluoride Nanoscintillators, Journal of Nanomaterials, Vol. 2011

microdevice. *Nat. Commun.* 2:403 doi: 10.1038/ncomms1412 (2011).

Separation during Spin Casting", *Adv. Funct. Mater.* 15 (2005).

deflections. *IEEE Trans. Nuc. Sci.* 52, 3005-3011 (2005).

Blended PbSe Nanosemiconductors (submitted, 2011).

control over the wave mechanics of high energy photons.

accompanied by a less expensive fabrication modality.

**4. Conclusion**

**5. References**

Vol. 9, (2010).

1321-1324, (2002).

(2011).

Fig. 16. (a) The carpet cloak design that transforms a mirror with a bump into a virtually flat mirror. Note the gradient index cloak above the bump, the pattern fabricated in a SOI wafer where the Si slab serves as a 2D waveguide. (b) SEM image of fabricated 21-layer fishnet structure, consisting of alternating layers of 30 nm silver and 50 nm magnesium fluoride (Valentine et al., 2011).

That is, the greatest challenge to achieving wave-guiding effects at x- or gamma-ray wavelengths, is that for existing metamaterials, the material loss and fabrication difficulties are substantial. As suggested above, the size of the nanostructure is generally subwavelength, so that the index of refraction of the material is governed by the effective medium approximation. The wavelength of a 1 keV x-ray is 1.23 nm; thus, a nanostructured metamaterial must have an ordered nano-crystalline structure in the nanometer range, which is beyond the capabilities of standard e-beam tools, and one must therefore deviate from the material-removal modality.

Fortunately, the desired size-scale can be realized with self-assembly, in which the current lower limit is in this nanometer scale and thus potentially applicable to x-ray cloaking. A combination of sol preparation and electrophoretic deposition has been used to synthesize a variety of oxide nanorod arrays, such as TiO2, SiO2, Nb2O5, V2O5, BaTiO3, Pb(Zr,Ti)O3, Sndoped In2O3 (ITO), and Sr2Nb2O7 (Kao, 2004). We have grown nanowires from CdTe and PbSe semiconductors, upon which metallic shells can be deposited. There has been a myriad of different self-assembled nanostructures, but they do not approach the process uniformity and control that accompanies batch-processing methods (cf. Ko et al., 2011) , and the deviations in the uniformity would diminish any wave-guiding achieved from a designed array of plasmonic structures of similar size. Nevertheless, some wave guiding can occur from an array of proper materials. Thus, using fabrication techniques similar to that that have been successfully employed to make high-performance charge-conversion devices, one can conceivably change the materials in the nanostructured array in order to excercise control over the wave mechanics of high energy photons.

## **4. Conclusion**

576 Current Topics in Ionizing Radiation Research

**a**

Fig. 16. (a) The carpet cloak design that transforms a mirror with a bump into a virtually flat mirror. Note the gradient index cloak above the bump, the pattern fabricated in a SOI wafer where the Si slab serves as a 2D waveguide. (b) SEM image of fabricated 21-layer fishnet structure, consisting of alternating layers of 30 nm silver and 50 nm magnesium fluoride

That is, the greatest challenge to achieving wave-guiding effects at x- or gamma-ray wavelengths, is that for existing metamaterials, the material loss and fabrication difficulties are substantial. As suggested above, the size of the nanostructure is generally subwavelength, so that the index of refraction of the material is governed by the effective medium approximation. The wavelength of a 1 keV x-ray is 1.23 nm; thus, a nanostructured metamaterial must have an ordered nano-crystalline structure in the nanometer range, which is beyond the capabilities of standard e-beam tools, and one must therefore deviate

Fortunately, the desired size-scale can be realized with self-assembly, in which the current lower limit is in this nanometer scale and thus potentially applicable to x-ray cloaking. A

(Valentine et al., 2011).

from the material-removal modality.

Nanostructured media allow us to measure ionizing radiation with greater precision than can be achieved with single-crystal media because one has greater experimental control over the detector's governing parameters- the size and shape of the nanoparticles- than can be equivalently achieved in a nominally single-crystal media, in which defects and impurities can readily spoil the performance of the sensor. More importantly, one can yield fundamentally superior detection characteristics because one has a mechanism through which the informational processes- such as electron creation- can be controlled relative to the loss processes- such as phonon excitation. Fortuitously, this superior physics is also accompanied by a less expensive fabrication modality.

Nanostructured materials have therefore been projected as the next-generation material for the detection of ionizing radiation, the adoption of which depends on overcoming the expected difficulties associated with using a composite material comprised of innumerable interfaces at which information can be lost. As we have shown in this chapter, methods exist that can quench interface trapping so that the promise of the material can be realized today.

#### **5. References**

Hammig, M.D; D. K. Wehe and J. A. Nees, , The measurement of sub-brownian lever deflections. *IEEE Trans. Nuc. Sci.* 52, 3005-3011 (2005).

**27**

*1Egypt 2KSA*

**Glass as Radiation Sensor**

*1National Research Centre, Glass Research Department, 2Chemistry Department, Faculty of Science, Taif University,*

Let's begin with what glass is not—it is not a crystal. The atoms in a crystal are organized in a regular, repetitive lattice so you need only locate a few atoms in order to predict where all of their neighbors are (Fig.1*a*). The atoms are so neatly arranged that, except for occasional crystal defects, you can predict positions for thousands or even millions of atoms in every

Fig. 1. (a), a crystalline solid with long-range order, (b), an amorphous solid, no long-range

**1. Introduction**

order.

**1.1 What is glass? [Noel, 1998]**

direction. This spatial regularity is called **long-range order**.

Amany A. El-Kheshen

## **Glass as Radiation Sensor**

## Amany A. El-Kheshen

*1National Research Centre, Glass Research Department, 2Chemistry Department, Faculty of Science, Taif University, 1Egypt 2KSA*

## **1. Introduction**

578 Current Topics in Ionizing Radiation Research

Kim, G.; J. Huang and M.D. Hammig, An Investigation of Nanocrystalline Semiconductor

Kim, G; M.D. Hammig, Development of Lead Chalcogenide Nanocrystalline (NC)

Klassen, N.V.; et al., Advantages and problems of nanocrystalline scintillators, IEEE Trans.

Lacy, J; et al., Boron-Coated Straw Detectors: a Novel Approach for Helium-3 Neutron

Murray, C.B.; et al., Colloidal synthesis of nanocrystals and nanocrystal superlattices, *IBM J.*

Olkhovets, A.; et al., Size-dependent temperature variation of the energy gap in lead-salt

Remacle, F. et al., Conductivity of 2-D Ag Quantum Dot Arrays: Computational Study of the

Rogach, A.L; et al., II-VI semiconductor nanocrystals in thin films and colloidal crystals,

Schaller, R. D., et al., Breaking the phonon bottleneck in semiconductor nanocrystals via

Ullom, J.N.; et al., Multiplexed microcalorimeter arrays for precision measurements from microwave to gamma-ray wavelengths. *Nucl. Inst. and Meth. A* 579 161-164 (2007). Withers, N.; et al., Lead-iodide-based nanoscintillators for detectino of ionizing radiation,

Zehnpfennig, J.; et al., Surface optomechanics: calculating optically excited acoustical whispering gallery modes in microspheres, *Optics Express*, vol. 19, 14241 (2011).

quantum dots, *Phys. Rev. Lett.,* vol. 81, pp. 3539-3542, (1998).

*Colloids Surf. A,* vol. 202, iss. 2-3, pp. 135-144, (2002).

*Sci.* 56 841-848 (2009).

pp. 4116-4126, (2002).

*Lett.,* vol. 95, 196401, (2005).

Proc. Of SPIE Vol. 7304, 73041N (2009).

on Nuc. Sci., Vol. 55, 1536-1541 (2008).

*Conference (2010 NSS/MIC)*, p 3971-5, (2010).

*Res. & Dev.*, vol. 45, no. 1, pp. 47-56, Jan. 2001.

1317-1320 (2009).

Assemblies as a Material Basis for Ionizing-Radiation Detectors. *IEEE Trans. Nuc.*

Semiconductor Ionizing Radiation Detectors. *2009 IEEE Nuc. Sci. Sym. Conf. Record,*

Detector Replacement, *2010 IEEE Nuclear Science Symposium and Medical Imaging*

Role of Size and Packing Disorder at Low Temperatures, *J. Phys. Chem.*, vol. 106,

multiphonon emission induced by intrinsic nonadiabatic interactions, *Phys. Rev.*

### **1.1 What is glass? [Noel, 1998]**

Let's begin with what glass is not—it is not a crystal. The atoms in a crystal are organized in a regular, repetitive lattice so you need only locate a few atoms in order to predict where all of their neighbors are (Fig.1*a*). The atoms are so neatly arranged that, except for occasional crystal defects, you can predict positions for thousands or even millions of atoms in every direction. This spatial regularity is called **long-range order**.

Fig. 1. (a), a crystalline solid with long-range order, (b), an amorphous solid, no long-range order.

Glass as Radiation Sensor 581

examples of Egyptian glassware are three vases bearing the name of the Pharaoh

The first instance of glass being used for windows in buildings, especially in Britain, was during the period of the Romans. In the 1st century A. D., it is known that the Romans used glass for a variety of reasons including mosaic tiles, decorating pottery and as windows. It seems that the glass window became more popular with the advent of churches and other places to worship. Most of the earliest examples of Roman window glass are colored, suggesting that they were glass windows for churches, for example. Around the world, the need for glass windows (and the manufacture of the glass) did not really take hold until the

The first types of glass invented centuries ago, scientists made that glass by mixing materials, melting and then cooling to form a solid. There are many different types of glass with different chemical and physical properties. Each can be made by a suitable adjustment

Glasses may be devised to meet almost any imaginable requirement. For many specialized applications in chemistry, pharmacy, the electrical andelectronics industries, optics, or the comparatively family of materials known as glass ceramics? Glass is a practical material for

Most of the glass we see around us in our everyday lives in the form of bottles and jars, flat glass for windows or for drinking glasses is known as commercial glass or soda-lime glass,

The main constituent of practically all commercial glass is sand. Sand by itself can be fused to produce glass but the temperature at which this can be achieved is ≥ 1700oC. Adding other minerals and chemicals to sand can considerably reduce the melting temperature. The addition of sodium carbonate (Na2CO3), known as soda ash, to produce a mixture of 75% silica (SiO2) and 25% of sodium oxide (Na2O), will reduce the temperature of fusion to about 800oC. However, a glass of this composition is water-soluble and is known as water glass. In order to give the glass its stability, other chemicals like calcium oxide (CaO) and

Commercial glass is normally colorless, allowing it to freely transmit light, which is what makes glass ideal for windows and many other uses. Additional chemicals have to be added

Most of commercial glasses have roughly similar chemical compositions of:

Thoutmosis 2I (1504-1450 B.C.).

**1.3 It only looks like magic (A world of glass)**

to chemical compositions, but the main types of glass are: - Commercial Glass also known as soda-lime glass

11th century.

the engineer to use.

**<IP_ADDRESS> Commercial glass**

as soda ash is used in its manufacture.

magnesium oxide (MgO) are needed.

to produce different colors of glass.

12wt% - 16wt% Na2O (sodium oxide) 5wt% - 11wt% CaO (calcium oxide) 1wt% - 3wt%MgO (magnesium oxide) 1wt% - 3wt% Al2O3 (aluminium oxide)

70wt% - 74wt% SiO2 (silica)

**1.3.1 First types of glass**

Glass is an **amorphous solid**, a material without long-range order (Fig. 1*b*). Locating a few glass atoms tells you nothing about where to find any other atoms. The atoms in glass are arranged in the random manner of a liquid because glass is essentially a super-stiff liquid. Its atoms are jumbled together in a sloppy fashion but they can't move about to form a more orderly arrangement. Glass arrives at this peculiar amorphous state when hot liquid glass is cooled too rapidly. If molten glass were an ordinary liquid, it would begin to solidify abruptly during cooling once it reached its freezing temperature. At that point, its atoms would begin to arrange themselves in crystals that would grow in size until there was no liquid left. That's what's normally meant by freezing. However some liquids are slow to crystallize when you cool them slightly below their freezing temperatures. While they may be cold enough to grow crystals, they must get those crystals started somehow. If crystallization doesn't start, material's atoms and molecules will continue to move about and it will behave as a liquid. When that happens, the liquid is said to be **supercooled**. Supercooling is common in liquids that have difficulties forming the initial **seed crystals** on which the rest of the liquid can crystallize. Because almost all of the atoms in a seed crystal are on its surface, it has a relatively large surface tension and surface energy. Below a certain critical size, a crystal is unstable and tends to fall apart rather than grow. However once the first seed crystals manage to form, a process called nucleation, the rest of the supercooled liquid may crystallize with startling rapidity. Just below its freezing temperature, the atoms in glass don't bind to one another long enough to form complete seed crystals, and nucleation takes almost forever. At somewhat lower temperatures, seed crystals begin to nucleate, but glass's large viscosity (thickness) prevents these crystals from growing quickly. The glass remains a supercooled liquid for an unusually long time. At even lower temperatures, glass becomes so viscous that crystal growth stops altogether. The glass is then a stable supercooled liquid. At this temperature range, glass still pours fairly easily and can be stretched or molded into almost any shape.

However, when you cool the glass still further, it becomes a *glass*. Here the word *glass* refers to a physical state of the material—a type of amorphous solid. To distinguish this use of the word glass from the common building material, it is italicized. Glass, the material, becomes a *glass*, the state, at the **glass transition temperature** (Tg). Below Tg, the atoms in the glass rarely move past one another; they continue to jiggle about with thermal energy but they don't travel about the material.

#### **1.2 A quick journey with glass [Gerry, M., 2002]**

The production of glass has been occurring naturally for millions of years, but the discovery of manufactured glass leads us to live a luxury life.

Natural glass has existed since the beginnings of time, formed when certain types of rocks melt as a result of high-temperature phenomena such as volcanic eruptions, lightning strikes or the impact of meteorites and then cool and solidify rapidly. The earliest man-made glass objects, mainly non-transparent glass beads, are thought to date back to around 3500 B.C., which found in Egypt. Phoenician merchants and sailors spread this new art along the coasts of the Mediterranean Sea.

After 1500 B.C., Egyptian craftsmen are known to have begun developing a method for producing glass pots by dipping a core mould of compacted sand into molten glass and then turning the mould so that molten glass adhered to it. While still soft, the glass-covered mould could then be rolled on a slab of stone in order to smooth or decorate it. The earliest

Glass is an **amorphous solid**, a material without long-range order (Fig. 1*b*). Locating a few glass atoms tells you nothing about where to find any other atoms. The atoms in glass are arranged in the random manner of a liquid because glass is essentially a super-stiff liquid. Its atoms are jumbled together in a sloppy fashion but they can't move about to form a more orderly arrangement. Glass arrives at this peculiar amorphous state when hot liquid glass is cooled too rapidly. If molten glass were an ordinary liquid, it would begin to solidify abruptly during cooling once it reached its freezing temperature. At that point, its atoms would begin to arrange themselves in crystals that would grow in size until there was no liquid left. That's what's normally meant by freezing. However some liquids are slow to crystallize when you cool them slightly below their freezing temperatures. While they may be cold enough to grow crystals, they must get those crystals started somehow. If crystallization doesn't start, material's atoms and molecules will continue to move about and it will behave as a liquid. When that happens, the liquid is said to be **supercooled**. Supercooling is common in liquids that have difficulties forming the initial **seed crystals** on which the rest of the liquid can crystallize. Because almost all of the atoms in a seed crystal are on its surface, it has a relatively large surface tension and surface energy. Below a certain critical size, a crystal is unstable and tends to fall apart rather than grow. However once the first seed crystals manage to form, a process called nucleation, the rest of the supercooled liquid may crystallize with startling rapidity. Just below its freezing temperature, the atoms in glass don't bind to one another long enough to form complete seed crystals, and nucleation takes almost forever. At somewhat lower temperatures, seed crystals begin to nucleate, but glass's large viscosity (thickness) prevents these crystals from growing quickly. The glass remains a supercooled liquid for an unusually long time. At even lower temperatures, glass becomes so viscous that crystal growth stops altogether. The glass is then a stable supercooled liquid. At this temperature range, glass still pours fairly easily and

However, when you cool the glass still further, it becomes a *glass*. Here the word *glass* refers to a physical state of the material—a type of amorphous solid. To distinguish this use of the word glass from the common building material, it is italicized. Glass, the material, becomes a *glass*, the state, at the **glass transition temperature** (Tg). Below Tg, the atoms in the glass rarely move past one another; they continue to jiggle about with thermal energy but they

The production of glass has been occurring naturally for millions of years, but the discovery

Natural glass has existed since the beginnings of time, formed when certain types of rocks melt as a result of high-temperature phenomena such as volcanic eruptions, lightning strikes or the impact of meteorites and then cool and solidify rapidly. The earliest man-made glass objects, mainly non-transparent glass beads, are thought to date back to around 3500 B.C., which found in Egypt. Phoenician merchants and sailors spread this new art along the

After 1500 B.C., Egyptian craftsmen are known to have begun developing a method for producing glass pots by dipping a core mould of compacted sand into molten glass and then turning the mould so that molten glass adhered to it. While still soft, the glass-covered mould could then be rolled on a slab of stone in order to smooth or decorate it. The earliest

can be stretched or molded into almost any shape.

**1.2 A quick journey with glass [Gerry, M., 2002]**

of manufactured glass leads us to live a luxury life.

don't travel about the material.

coasts of the Mediterranean Sea.

examples of Egyptian glassware are three vases bearing the name of the Pharaoh Thoutmosis 2I (1504-1450 B.C.).

The first instance of glass being used for windows in buildings, especially in Britain, was during the period of the Romans. In the 1st century A. D., it is known that the Romans used glass for a variety of reasons including mosaic tiles, decorating pottery and as windows. It seems that the glass window became more popular with the advent of churches and other places to worship. Most of the earliest examples of Roman window glass are colored, suggesting that they were glass windows for churches, for example. Around the world, the need for glass windows (and the manufacture of the glass) did not really take hold until the 11th century.

### **1.3 It only looks like magic (A world of glass) 1.3.1 First types of glass**

The first types of glass invented centuries ago, scientists made that glass by mixing materials, melting and then cooling to form a solid. There are many different types of glass with different chemical and physical properties. Each can be made by a suitable adjustment to chemical compositions, but the main types of glass are:

Glasses may be devised to meet almost any imaginable requirement. For many specialized applications in chemistry, pharmacy, the electrical andelectronics industries, optics, or the comparatively family of materials known as glass ceramics? Glass is a practical material for the engineer to use.

### **<IP_ADDRESS> Commercial glass**

Most of the glass we see around us in our everyday lives in the form of bottles and jars, flat glass for windows or for drinking glasses is known as commercial glass or soda-lime glass, as soda ash is used in its manufacture.

The main constituent of practically all commercial glass is sand. Sand by itself can be fused to produce glass but the temperature at which this can be achieved is ≥ 1700oC. Adding other minerals and chemicals to sand can considerably reduce the melting temperature.

The addition of sodium carbonate (Na2CO3), known as soda ash, to produce a mixture of 75% silica (SiO2) and 25% of sodium oxide (Na2O), will reduce the temperature of fusion to about 800oC. However, a glass of this composition is water-soluble and is known as water glass. In order to give the glass its stability, other chemicals like calcium oxide (CaO) and magnesium oxide (MgO) are needed.

Commercial glass is normally colorless, allowing it to freely transmit light, which is what makes glass ideal for windows and many other uses. Additional chemicals have to be added to produce different colors of glass.

Most of commercial glasses have roughly similar chemical compositions of:

70wt% - 74wt% SiO2 (silica)

12wt% - 16wt% Na2O (sodium oxide)

5wt% - 11wt% CaO (calcium oxide)

1wt% - 3wt%MgO (magnesium oxide)

1wt% - 3wt% Al2O3 (aluminium oxide)

Glass as Radiation Sensor 583

In recent years, great progress has been made in making optical fibers which can guide light and thus transmit images round corners. These fibers are used in endoscopes for examination of internal human organs, changeable traffic message signs now on motorways for speed restriction warnings and communications technology, without which telephones

Types of special glass change according to human needs and development. Earlier, the

Silica glass or vitreous silica is of considerable technical importance as it has a very low thermal expansion. This glass contains tiny holes and is used for filtration. Porous glasses of

An important type of glass, aluminosilicate, contains 20wt% aluminium oxide (alumina-Al2O3), often including calcium oxide, magnesium oxide and boric oxide in relatively small amounts, with very small amounts of soda or potash. It is able to withstand high temperatures and thermal shock and is typically used in combustion tubes, gauge glasses for high-pressure steam boilers, and in halogen-tungsten lamps capable of operating at

Without this type of glass, watching TV would be very dangerous. A television produces Xrays that must be absorbed; otherwise they could in the long run cause health problems. The X-rays are absorbed by glass with minimum amounts of heavy oxides (lead, barium or strontium). Lead glass is commonly used for the funnel and neck of the TV tube, while glass

Without borate glass, the computer revolution would not have been possible as it's vitally important in producing electrical components. This type of glass contains little or no silica and is used for soldering glass, metals or ceramics as it melts at the relatively low

Glass of a slightly different composition is used for protecting siliconsemi-conductor components against chemical attack and mechanical damage, known as passivation glass. Chalcogenide glass, similar semi conductor effect, is a type of glass that can be made without the presence of oxygen. Some of them have potential use as infrared transmitting materials and as switching devices in computer memories because their conductivity

Technical is the term given to a range of glasses used in the electronics industry.

temperature (450-550oC), below that of normal glass, ceramics and many metals.

changes abruptly when particular voltage values are exceeded.

and the internet would not be possible.

**1.3.2 Special glass**

 Vitreous silica Aluminosilicate glass Alkali-barium silicate glass

 Technical Glass Glass Ceramics Optical glass Sealing glass

special types of glass were:

**<IP_ADDRESS> Vitreous silica glass**

**<IP_ADDRESS> Alumino-silicate glass**

temperature as high as 750°C. **<IP_ADDRESS> Alkali-barium silicate glass**

**<IP_ADDRESS> Technical glass**

this kind are commonly known as Vycor.

containing barium is used for the screen.

Flat glass is similar in composition to container glass except that it contains a higher proportion of magnesium oxide.

Within these limits the composition is varied to suit a particular product and production method. The raw materials are carefully weighed and thoroughly mixed, as consistency of composition is of utmost importance in making glass.

Nowadays, recycled glass from bottle banks collections, known as cullet, is used to make new glass. Using cullet has many environmental benefits, it prevents pollution by reducing quarrying, and because cullet melts more easily, it saves energy.

Almost any proportion of cullet can be added to the mix (known as batch), but in the right condition. Although the recycled glass may come from manufacturers around the world, it can be used by any glassmaker, as the container glass compositions are very similar. It is however important, that glass colors are not mixed and that the cullet is free from impurities, especially metals and ceramics.

## **<IP_ADDRESS> Lead glass**

Commonly known as lead crystal, lead glass is used to make a wide variety of decorative glass objects.

It is made by using lead oxide instead of calcium oxide, and potassium oxide instead of all or most of the sodium oxide. The traditional English full lead crystal contains at least 30% lead oxide (PbO) but any glass containing at least 24% PbO can be described as lead crystal. Glass containing less than 24% PbO, is known simply as crystal glass. The lead is locked into the chemical structure of the glass so there is no risk to human health.

Lead glass has a high refractive index making it sparkle brightly and a relatively soft surface so that it is easy to decorate by cutting and engraving which highlights the crystal's brilliance making it popular for glasses, decanters and other decorative objects.

Glass with even higher lead oxide contents (typically 65%) may be used as radiation shielding because of the well-known ability of lead to absorb gamma rays and other forms of harmful radiation.

## **<IP_ADDRESS> Borosilicate glass**

Most of us are more familiar with this type of glass in the form of ovenware and other heatresisting ware, better known under the trade name Pyrex.

Borosilicate glass, the third major group, is made mainly of silica (70-80wt %) and boric oxide (7-13wt %) with smaller amounts of the alkalis (sodium and potassium oxides) and aluminum oxide. This type of glass has relatively low alkali content and consequently has good chemical durability and thermal shock resistance. As a result it is widely used in the chemical industry, for laboratory apparatus, for ampoules and other pharmaceutical containers and as glass fibers for textile and plastic reinforcement.

### **<IP_ADDRESS> Glass fiber**

Glass fiber has many uses from roof insulation to medical equipment and its composition varies depending on its application.

For building insulation, the type of glass used is normally soda lime. For textiles, an alumino-borosilicate glass with very low sodium oxide content is preferred because of its good chemical durability and high softening point. This is also the type of glass fiber used in the reinforced plastics to make protective helmets, boats, piping, car chassis, ropes, car exhausts and many other items.

Flat glass is similar in composition to container glass except that it contains a higher

Within these limits the composition is varied to suit a particular product and production method. The raw materials are carefully weighed and thoroughly mixed, as consistency of

Nowadays, recycled glass from bottle banks collections, known as cullet, is used to make new glass. Using cullet has many environmental benefits, it prevents pollution by reducing

Almost any proportion of cullet can be added to the mix (known as batch), but in the right condition. Although the recycled glass may come from manufacturers around the world, it can be used by any glassmaker, as the container glass compositions are very similar. It is however important, that glass colors are not mixed and that the cullet is free from

Commonly known as lead crystal, lead glass is used to make a wide variety of decorative

It is made by using lead oxide instead of calcium oxide, and potassium oxide instead of all or most of the sodium oxide. The traditional English full lead crystal contains at least 30% lead oxide (PbO) but any glass containing at least 24% PbO can be described as lead crystal. Glass containing less than 24% PbO, is known simply as crystal glass. The lead is locked into

Lead glass has a high refractive index making it sparkle brightly and a relatively soft surface so that it is easy to decorate by cutting and engraving which highlights the crystal's

Glass with even higher lead oxide contents (typically 65%) may be used as radiation shielding because of the well-known ability of lead to absorb gamma rays and other forms

Most of us are more familiar with this type of glass in the form of ovenware and other heat-

Borosilicate glass, the third major group, is made mainly of silica (70-80wt %) and boric oxide (7-13wt %) with smaller amounts of the alkalis (sodium and potassium oxides) and aluminum oxide. This type of glass has relatively low alkali content and consequently has good chemical durability and thermal shock resistance. As a result it is widely used in the chemical industry, for laboratory apparatus, for ampoules and other pharmaceutical

Glass fiber has many uses from roof insulation to medical equipment and its composition

For building insulation, the type of glass used is normally soda lime. For textiles, an alumino-borosilicate glass with very low sodium oxide content is preferred because of its good chemical durability and high softening point. This is also the type of glass fiber used in the reinforced plastics to make protective helmets, boats, piping, car chassis, ropes, car

proportion of magnesium oxide.

composition is of utmost importance in making glass.

impurities, especially metals and ceramics.

**<IP_ADDRESS> Lead glass**

of harmful radiation. **<IP_ADDRESS> Borosilicate glass**

**<IP_ADDRESS> Glass fiber**

varies depending on its application.

exhausts and many other items.

glass objects.

quarrying, and because cullet melts more easily, it saves energy.

the chemical structure of the glass so there is no risk to human health.

resisting ware, better known under the trade name Pyrex.

containers and as glass fibers for textile and plastic reinforcement.

brilliance making it popular for glasses, decanters and other decorative objects.

In recent years, great progress has been made in making optical fibers which can guide light and thus transmit images round corners. These fibers are used in endoscopes for examination of internal human organs, changeable traffic message signs now on motorways for speed restriction warnings and communications technology, without which telephones and the internet would not be possible.

## **1.3.2 Special glass**

Types of special glass change according to human needs and development. Earlier, the special types of glass were:

## **<IP_ADDRESS> Vitreous silica glass**

Silica glass or vitreous silica is of considerable technical importance as it has a very low thermal expansion. This glass contains tiny holes and is used for filtration. Porous glasses of this kind are commonly known as Vycor.

#### **<IP_ADDRESS> Alumino-silicate glass**

An important type of glass, aluminosilicate, contains 20wt% aluminium oxide (alumina-Al2O3), often including calcium oxide, magnesium oxide and boric oxide in relatively small amounts, with very small amounts of soda or potash. It is able to withstand high temperatures and thermal shock and is typically used in combustion tubes, gauge glasses for high-pressure steam boilers, and in halogen-tungsten lamps capable of operating at temperature as high as 750°C.

#### **<IP_ADDRESS> Alkali-barium silicate glass**

Without this type of glass, watching TV would be very dangerous. A television produces Xrays that must be absorbed; otherwise they could in the long run cause health problems. The X-rays are absorbed by glass with minimum amounts of heavy oxides (lead, barium or strontium). Lead glass is commonly used for the funnel and neck of the TV tube, while glass containing barium is used for the screen.

#### **<IP_ADDRESS> Technical glass**

Technical is the term given to a range of glasses used in the electronics industry.

Without borate glass, the computer revolution would not have been possible as it's vitally important in producing electrical components. This type of glass contains little or no silica and is used for soldering glass, metals or ceramics as it melts at the relatively low temperature (450-550oC), below that of normal glass, ceramics and many metals.

Glass of a slightly different composition is used for protecting siliconsemi-conductor components against chemical attack and mechanical damage, known as passivation glass.

Chalcogenide glass, similar semi conductor effect, is a type of glass that can be made without the presence of oxygen. Some of them have potential use as infrared transmitting materials and as switching devices in computer memories because their conductivity changes abruptly when particular voltage values are exceeded.

Glass as Radiation Sensor 585

Once the methods of colored glass production was discovered, an explosion of experimentation began. The goal was to find substances that would produce specific colors in the glass. Some of the earliest objects made from glass were small cups, bottles and

Religious organizations were among those who provided incentive to the early glass artisans. Stained glass windows became very popular additions to churches and mosques over 1000 years ago. These artists needed a full palette of colors to make a realistic stained glass scene. This search for a full palette fueled research and experimentation to produce a

Then, another problem was discovered. Many of the glass colors did not stand up to year-in, year-out exposure to the direct rays of the sun. The result was a stained glass scene of deteriorating beauty. Some colors darkened or changed over time, while others faded away. Research and experimentation continued in an effort to meet the need for colors of duration.

The recipe for producing colored glass usually involves the adding of a metal to the glass. This is often accomplished by adding some powdered oxide, sulfide or other compound of that metal to the glass while it is molten. The table below lists some of the coloring agents of glass and the colors that they produce. Manganese dioxide and sodium nitrate are also listed. They are discoloring agents - materials that neutralize the coloring impact of

Eventually a full palette of fairly stable colors was achieved.

Yellow Cadmium Sulfide Red Gold Chloride Blue-Violet Cobalt Oxide Purple Manganese Dioxide Violet Nickel Oxide Yellow-Amber Sulfur

Emerald Green Chromic Oxide Fluorescent Yellow, Green Uranium Oxide Greens and Browns Iron Oxide Reds Selenium Oxide Amber Brown Carbon Oxides White Antimony Oxides Blue, Green, Red Copper Compounds White Tin Compounds Yellow Lead Compounds A "decoloring" agent Manganese Dioxide A "decoloring" agent Sodium Nitrate

*<IP_ADDRESS>.2 The glass color palette*

ornaments.

vast array of colors. *<IP_ADDRESS>.3 Colors of duration*

*I.<IP_ADDRESS> Metals used to color glass*

Metals Used to Impart Color to Glass

impurities in the glass.

Table 1.

## **<IP_ADDRESS> Glass ceramic**

Some of these "Glass ceramics", formed typically from lithium aluminosilicate glass, are extremely resistant to thermal shock and have found several applications where this property is important, including cooking ware, mirror substrates for astronomical telescopes and missile nose cones.

An essential feature of glass is that it does not contain crystals. However, by deliberately stimulating crystal growth in glass, it is possible to produce a type of glass with a controlled amount of crystallization that can combine many of the best features of ceramics and glass.

## **<IP_ADDRESS> Optical glass**

Optical glasses are found in scientific instruments, microscopes, and fighter aircraft and most commonly in spectacles.

The most important properties are the refractive index and the dispersion. The index is a measure of how much the glass bends light. The dispersion is a measure of the way the glass splits white light into the colors of the rainbow. Glass makers use the variations in these characteristics to develop optical glasses.

### **<IP_ADDRESS> Sealing glass**

A wide variety of glass compositions are used to seal metals for electrical and electronic components. Here the available glasses may be grouped according to their thermal expansion which must be matched with the thermal expansions of the respective metals so that sealing is possible without excessive strain being induced by differing levels of expansion.

For sealing to tungsten, in making incandescent and discharge lamps, borosilicate alkaline earths or aluminous silicate glasses are suitable. Sodium borosilicate glasses may be used for sealing to molybdenum and the iron-nickel-cobalt (Fernico) alloys, are frequently employed as a substitute. The amount of sodium oxide permissible depending on the degree of electrical resistance required. With glasses designed to seal to Kovar alloy, relatively high contents of boric oxide (approximately 20%) are needed to keep the transformation temperature low and usually the preferred alkali is potassium oxide so as to ensure high electrical insulation.

Where the requirement for electrical insulation is paramount, as in many types of vacuum tube and for the encapsulation of diodes, a variety of lead glasses (typical containing between 30% and 60% lead oxide) can be used.

## **<IP_ADDRESS> Colored glase (Weyl, 1959 )**

Color is the most obvious property of a glass object. It can also be one of the most interesting and beautiful properties. Although color rarely defines the usefulness of a glass object it almost always defines its desirability.

### *<IP_ADDRESS>.1 The colored glass recipe*

The earliest people who worked with glass had no control over its color. Then, through accident and experimentation glass makers learned that adding certain substances to the glass melt would produce spectacular colors in the finished product. Other substances were discovered that, when added to the melt, would remove color from the finished project.

The Egyptians and the Romans both became expert at the production of colored glass. In the eighth century, an Arab chemist known as "Gerber" recorded dozens of formulas for the production of glass in specific colors. Gerber is often known as the "father of chemistry" and he realized that the oxides of metals were the key ingredients for coloring glass.

Some of these "Glass ceramics", formed typically from lithium aluminosilicate glass, are extremely resistant to thermal shock and have found several applications where this property is important, including cooking ware, mirror substrates for astronomical telescopes

An essential feature of glass is that it does not contain crystals. However, by deliberately stimulating crystal growth in glass, it is possible to produce a type of glass with a controlled amount of crystallization that can combine many of the best features of ceramics and glass.

Optical glasses are found in scientific instruments, microscopes, and fighter aircraft and

The most important properties are the refractive index and the dispersion. The index is a measure of how much the glass bends light. The dispersion is a measure of the way the glass splits white light into the colors of the rainbow. Glass makers use the variations in these

A wide variety of glass compositions are used to seal metals for electrical and electronic components. Here the available glasses may be grouped according to their thermal expansion which must be matched with the thermal expansions of the respective metals so that sealing is possible without excessive strain being induced by differing levels of

For sealing to tungsten, in making incandescent and discharge lamps, borosilicate alkaline earths or aluminous silicate glasses are suitable. Sodium borosilicate glasses may be used for sealing to molybdenum and the iron-nickel-cobalt (Fernico) alloys, are frequently employed as a substitute. The amount of sodium oxide permissible depending on the degree of electrical resistance required. With glasses designed to seal to Kovar alloy, relatively high contents of boric oxide (approximately 20%) are needed to keep the transformation temperature low and usually the preferred alkali is potassium oxide so as to ensure high

Where the requirement for electrical insulation is paramount, as in many types of vacuum tube and for the encapsulation of diodes, a variety of lead glasses (typical containing

Color is the most obvious property of a glass object. It can also be one of the most interesting and beautiful properties. Although color rarely defines the usefulness of a glass object it

The earliest people who worked with glass had no control over its color. Then, through accident and experimentation glass makers learned that adding certain substances to the glass melt would produce spectacular colors in the finished product. Other substances were discovered that, when added to the melt, would remove color from the finished project. The Egyptians and the Romans both became expert at the production of colored glass. In the eighth century, an Arab chemist known as "Gerber" recorded dozens of formulas for the production of glass in specific colors. Gerber is often known as the "father of chemistry" and

he realized that the oxides of metals were the key ingredients for coloring glass.

**<IP_ADDRESS> Glass ceramic**

and missile nose cones.

**<IP_ADDRESS> Optical glass**

**<IP_ADDRESS> Sealing glass**

electrical insulation.

expansion.

most commonly in spectacles.

characteristics to develop optical glasses.

between 30% and 60% lead oxide) can be used.

**<IP_ADDRESS> Colored glase (Weyl, 1959 )**

almost always defines its desirability.

*<IP_ADDRESS>.1 The colored glass recipe*

#### *<IP_ADDRESS>.2 The glass color palette*

Once the methods of colored glass production was discovered, an explosion of experimentation began. The goal was to find substances that would produce specific colors in the glass. Some of the earliest objects made from glass were small cups, bottles and ornaments.

Religious organizations were among those who provided incentive to the early glass artisans. Stained glass windows became very popular additions to churches and mosques over 1000 years ago. These artists needed a full palette of colors to make a realistic stained glass scene. This search for a full palette fueled research and experimentation to produce a vast array of colors.

#### *<IP_ADDRESS>.3 Colors of duration*

Then, another problem was discovered. Many of the glass colors did not stand up to year-in, year-out exposure to the direct rays of the sun. The result was a stained glass scene of deteriorating beauty. Some colors darkened or changed over time, while others faded away. Research and experimentation continued in an effort to meet the need for colors of duration. Eventually a full palette of fairly stable colors was achieved.

#### *I.<IP_ADDRESS> Metals used to color glass*

Table 1.

The recipe for producing colored glass usually involves the adding of a metal to the glass. This is often accomplished by adding some powdered oxide, sulfide or other compound of that metal to the glass while it is molten. The table below lists some of the coloring agents of glass and the colors that they produce. Manganese dioxide and sodium nitrate are also listed. They are discoloring agents - materials that neutralize the coloring impact of impurities in the glass.

Glass as Radiation Sensor 587

Dense materials are needed for shielding from gamma radiation. Clothing provides little shielding from penetrating radiation, but will prevent contamination of the skin by gamma-

Gamma radiation is easily detected by survey meters with a sodium iodide detector probe. Gamma radiation and/or characteristic x rays frequently accompany the emission of alpha

Examples of some gamma emitters: iodine-131, cesium-137, cobalt-60, radium-226, and

**Jiawei Shenga (2009)** studied the effect of UV-laser irradiation on the soda-lime silicate glass by preparing Commercial soda-lime silicate glass substrates composed of (wt%): 73.2 SiO2, 15.3 Na2O, 1.3 Al2O3, and 10.2 CaO, they found that As shown in Fig. 1, the asquenched base glass was colorless and had no measurable absorptions in the visible region. In addition, no ESR signal was observed in the blank samples. After laser irradiation, two characteristic absorption bands in the visible region with maxima at about 620, and 430 nm, respectively, were observed. More precise peak positions were determined to be 627 and 431 nm for these two bands, respectively, with the assistance of Gaussian resolution [**Friebele 1991, Marshall 1997, Zhang 2007**] (Fig. 2,). As a result, the glass showed slight brown. The induced color was unstable, as indicated by the decease of the peak intensity after 50 h room temperature storage following the irradiation (Fig. 2). These results were similar to the case using X-ray radiation [**Sheng, 1970**]. Radiation may cause the displacement of lattice atoms or electron defects that involve changes in the valence state of lattice or impurity atoms. The ionizing radiation produces electron-hole pairs in the glass structure. Accordingly, new optical absorption bands were developed [**Sheng, 1970**]. In general, these absorptions are associated with either oxygen deficiency or oxygen excess in the glass network. The most fundamental radiation-induced defects in glass are the nonbridging oxygen hole center (NBOHC: ^Si–O\*), the E' center (^Si\*), the peroxy radical (POR: ^Si–O–O\*), and the trapped electrons (TE), where the notation ''^'' represents three bonds with other oxygen in the glass network and ''\*'' denotes an unpaired electron. According to current knowledge, absorption bands of 627 and 431 nm in the soda-lime silicate glass were identified mainly as absorption of NBOHCs [**Bishay, 1970, Wong, 1967, Sheng, 2007**]. The main absorptions of the E0 center and the POR are in the far UV region, which have less effect on the glass visible color. Fig. 3 shows the ESR spectrum of the glass after the irradiation. Two distinctive signals at g ¼ 1.99w2.00 and g ¼ 1.992, respectively, were observed. As expected, the g ¼ 1.99w2.00 was identified as the defects of NBOHCs, correlating bands of 627 and 431 nm. The signal of g ¼ 1.992 might attribute to the defect of E' center. The spectra of the induced absorption with varying exposure time are presented in Fig. 4. The peak heights of the induced absorption increased with the laser irradiation time, and the peak positions absorption band were relatively constant, suggesting that only variations of their populations of defects be effected by the irradiation time. As shown in Fig. 4 (insert), the absorptions at 627 or 431 nm increased rapidly during the first 30 min radiation. The increase was then slow down and no more increase was observed after 60 min radiation. Irradiation energy is another important factor that affects the induced absorption of glass. As can be seen in Fig. 5, the induced absorption increased when the energy density was increased, while the induced absorption

emitting radioactive materials.

technetium-99m.

**2.1 Silicate glass**

and beta radiation during radioactive decay.

peak positions were relatively constant.

**2. Effect of radiation on different types of glass**

## **1.4 What types of radiation are there?**

The radiation one typically encounters is one of four types: alpha radiation, beta radiation, gamma radiation, and x radiation. Neutron radiation is also encountered in nuclear power plants and high-altitude flight and emitted from some industrial radioactive sources.

## **1.4.1 Alpha radiation**

Alpha radiation is a heavy, very short-range particle and is actually an ejected helium nucleus. Some characteristics of alpha radiation are:

Most alpha radiation is not able to penetrate human skin.

Alpha-emitting materials can be harmful to humans if the materials are inhaled, swallowed, or absorbed through open wounds.

A variety of instruments has been designed to measure alpha radiation. Special training in the use of these instruments is essential for making accurate measurements.

A thin-window Geiger-Mueller (GM) probe can detect the presence of alpha radiation.

Instruments cannot detect alpha radiation through even a thin layer of water, dust, paper, or other material, because alpha radiation is not penetrating.

Alpha radiation travels only a short distance (a few inches) in air, but is not an external hazard. Alpha radiation is not able to penetrate clothing. Examples of some alpha emitters: radium, radon, uranium, thorium.

## **1.4.2 Beta radiation**

Beta radiation is a light, short-range particle and is actually an ejected electron. Some characteristics of beta radiation are:

Beta radiation may travel several feet in air and is moderately penetrating.

Beta radiation can penetrate human skin to the "germinal layer," where new skin cells are produced. If high levels of beta-emitting contaminants are allowed to remain on the skin for a prolonged period of time, they may cause skin injury.

Beta-emitting contaminants may be harmful if deposited internally.

Most beta emitters can be detected with a survey instrument and a thin-window GM probe (e.g., "pancake" type). Some beta emitters, however, produce very low-energy, poorly penetrating radiation that may be difficult or impossible to detect. Examples of these difficult-to-detect beta emitters are hydrogen-3 (tritium), carbon-14, and sulfur-35.

Clothing provides some protection against beta radiation. Examples of some pure beta emitters: strontium-90, carbon-14, tritium, and sulfur-35.

## **1.4.3 Gamma and X- radiation**

Gamma radiation and x rays are highly penetrating electromagnetic radiation. Some characteristics of these radiations are:

Gamma radiation or x rays are able to travel many feet in air and many inches in human tissue. They readily penetrate most materials and are sometimes called "penetrating" radiation.

X rays are like gamma rays. X rays, too, are penetrating radiation. Sealed radioactive sources and machines that emit gamma radiation and x rays respectively constitute mainly an external hazard to humans.

Gamma radiation and x rays are electromagnetic radiation like visible light, radio waves, and ultraviolet light. These electromagnetic radiations differ only in the amount of energy they have. Gamma rays and x rays are the most energetic of these.

The radiation one typically encounters is one of four types: alpha radiation, beta radiation, gamma radiation, and x radiation. Neutron radiation is also encountered in nuclear power

Alpha radiation is a heavy, very short-range particle and is actually an ejected helium

Alpha-emitting materials can be harmful to humans if the materials are inhaled, swallowed,

A variety of instruments has been designed to measure alpha radiation. Special training in

Alpha radiation travels only a short distance (a few inches) in air, but is not an external hazard. Alpha radiation is not able to penetrate clothing. Examples of some alpha emitters: radium,

Beta radiation is a light, short-range particle and is actually an ejected electron. Some

Beta radiation can penetrate human skin to the "germinal layer," where new skin cells are produced. If high levels of beta-emitting contaminants are allowed to remain on the skin for

Most beta emitters can be detected with a survey instrument and a thin-window GM probe (e.g., "pancake" type). Some beta emitters, however, produce very low-energy, poorly penetrating radiation that may be difficult or impossible to detect. Examples of these

Clothing provides some protection against beta radiation. Examples of some pure beta

Gamma radiation and x rays are highly penetrating electromagnetic radiation. Some

Gamma radiation or x rays are able to travel many feet in air and many inches in human tissue. They readily penetrate most materials and are sometimes called "penetrating"

X rays are like gamma rays. X rays, too, are penetrating radiation. Sealed radioactive sources and machines that emit gamma radiation and x rays respectively constitute mainly an

Gamma radiation and x rays are electromagnetic radiation like visible light, radio waves, and ultraviolet light. These electromagnetic radiations differ only in the amount of energy

difficult-to-detect beta emitters are hydrogen-3 (tritium), carbon-14, and sulfur-35.

A thin-window Geiger-Mueller (GM) probe can detect the presence of alpha radiation. Instruments cannot detect alpha radiation through even a thin layer of water, dust, paper, or

the use of these instruments is essential for making accurate measurements.

Beta radiation may travel several feet in air and is moderately penetrating.

Beta-emitting contaminants may be harmful if deposited internally.

they have. Gamma rays and x rays are the most energetic of these.

plants and high-altitude flight and emitted from some industrial radioactive sources.

**1.4 What types of radiation are there?**

or absorbed through open wounds.

characteristics of beta radiation are:

**1.4.3 Gamma and X- radiation**

external hazard to humans.

radiation.

characteristics of these radiations are:

nucleus. Some characteristics of alpha radiation are: Most alpha radiation is not able to penetrate human skin.

other material, because alpha radiation is not penetrating.

a prolonged period of time, they may cause skin injury.

emitters: strontium-90, carbon-14, tritium, and sulfur-35.

**1.4.1 Alpha radiation**

radon, uranium, thorium.

**1.4.2 Beta radiation**

Dense materials are needed for shielding from gamma radiation. Clothing provides little shielding from penetrating radiation, but will prevent contamination of the skin by gammaemitting radioactive materials.

Gamma radiation is easily detected by survey meters with a sodium iodide detector probe.

Gamma radiation and/or characteristic x rays frequently accompany the emission of alpha and beta radiation during radioactive decay.

Examples of some gamma emitters: iodine-131, cesium-137, cobalt-60, radium-226, and technetium-99m.

## **2. Effect of radiation on different types of glass**

#### **2.1 Silicate glass**

**Jiawei Shenga (2009)** studied the effect of UV-laser irradiation on the soda-lime silicate glass by preparing Commercial soda-lime silicate glass substrates composed of (wt%): 73.2 SiO2, 15.3 Na2O, 1.3 Al2O3, and 10.2 CaO, they found that As shown in Fig. 1, the asquenched base glass was colorless and had no measurable absorptions in the visible region. In addition, no ESR signal was observed in the blank samples. After laser irradiation, two characteristic absorption bands in the visible region with maxima at about 620, and 430 nm, respectively, were observed. More precise peak positions were determined to be 627 and 431 nm for these two bands, respectively, with the assistance of Gaussian resolution [**Friebele 1991, Marshall 1997, Zhang 2007**] (Fig. 2,). As a result, the glass showed slight brown. The induced color was unstable, as indicated by the decease of the peak intensity after 50 h room temperature storage following the irradiation (Fig. 2). These results were similar to the case using X-ray radiation [**Sheng, 1970**]. Radiation may cause the displacement of lattice atoms or electron defects that involve changes in the valence state of lattice or impurity atoms. The ionizing radiation produces electron-hole pairs in the glass structure. Accordingly, new optical absorption bands were developed [**Sheng, 1970**]. In general, these absorptions are associated with either oxygen deficiency or oxygen excess in the glass network. The most fundamental radiation-induced defects in glass are the nonbridging oxygen hole center (NBOHC: ^Si–O\*), the E' center (^Si\*), the peroxy radical (POR: ^Si–O–O\*), and the trapped electrons (TE), where the notation ''^'' represents three bonds with other oxygen in the glass network and ''\*'' denotes an unpaired electron. According to current knowledge, absorption bands of 627 and 431 nm in the soda-lime silicate glass were identified mainly as absorption of NBOHCs [**Bishay, 1970, Wong, 1967, Sheng, 2007**]. The main absorptions of the E0 center and the POR are in the far UV region, which have less effect on the glass visible color. Fig. 3 shows the ESR spectrum of the glass after the irradiation. Two distinctive signals at g ¼ 1.99w2.00 and g ¼ 1.992, respectively, were observed. As expected, the g ¼ 1.99w2.00 was identified as the defects of NBOHCs, correlating bands of 627 and 431 nm. The signal of g ¼ 1.992 might attribute to the defect of E' center. The spectra of the induced absorption with varying exposure time are presented in Fig. 4. The peak heights of the induced absorption increased with the laser irradiation time, and the peak positions absorption band were relatively constant, suggesting that only variations of their populations of defects be effected by the irradiation time. As shown in Fig. 4 (insert), the absorptions at 627 or 431 nm increased rapidly during the first 30 min radiation. The increase was then slow down and no more increase was observed after 60 min radiation. Irradiation energy is another important factor that affects the induced absorption of glass. As can be seen in Fig. 5, the induced absorption increased when the energy density was increased, while the induced absorption peak positions were relatively constant.

Glass as Radiation Sensor 589

Fig. 4. Radiation induced optical Absorption with varied irradiation time (75 mJ / cm2 )

Fig. 5. Optical absorption affected by irradiation energy (100 shots) (insert: Optical

absorption affected by irradiation energy).

(insert: Optical absorptions affected by irradiation time)

Fig. 2. Optical absorption in soda-lime silicate glass after UV-laser irradiation at 75 mJ/cm2 for 10 min (insert Gaussian resolution of induced absorption)

Fig. 3. ESR spectra of glass after irradiation at 75 mJ / cm2 for 10 min

Fig. 2. Optical absorption in soda-lime silicate glass after UV-laser irradiation at 75 mJ/cm2

for 10 min (insert Gaussian resolution of induced absorption)

Fig. 3. ESR spectra of glass after irradiation at 75 mJ / cm2 for 10 min

Fig. 4. Radiation induced optical Absorption with varied irradiation time (75 mJ / cm2 ) (insert: Optical absorptions affected by irradiation time)

Fig. 5. Optical absorption affected by irradiation energy (100 shots) (insert: Optical absorption affected by irradiation energy).

Glass as Radiation Sensor 591

Fig. 7. Absorption spectra of CoO-doped sodium phosphate glasses with constant 0.25% CoO with additional 5% or 10% of Na2O or 5% or 10% P2O5 before and after

gamma irradiation.

**Gusarov et al (2010)** studied the effect of gamma irradiation on Silica-soda-lime glass with a composition 75SiO2–22Na2O–3CaO, wt.% (labelled R1) and the same glass doped with 0.05 wt.% CeO2 (labelled R7) were melted from high purity raw components using a technology which allowed one to keep the concentration of impurities of Fe ions at a few ppm and other transition metals below 1 ppm. Experimental samples were prepared as plates 25×25mm2, 1mm thick, and polished for optical measurements. The glass samples contained a small number of air bubbles with diameters up to 0.1mm, however transmission measurements at different parts on several samples showed that their influence was below the detection level. All transmission spectra were measured from 195 to 3300 nm with a commercial double-beam UV–Vis–NIR spectrophotometer. Irradiations have been performed in the Brigitte gamma irradiation facility at SCK CEN at 70, 200, and 350 ◦C, 25 kGy/h. They found that the addition ofCeO2 results in significant transmission degradation in the UV (Fig. 6)

Fig. 6. Optical absorption spectra of R1-5 and R7-5 glass samples in the UV range. For each glass two spectra are plotted: before and after annealing for 24 h at 350 ◦C

This degradation is due to the overlapping optical absorption bands of Ce3+ and Ce4+ ions, with maxima at 313 and 240 nm (3.96 and 5.15 eV), respectively [**Arbuzov, 1990**]. Above 350 nm both materials show the same high transmission with no observable optical absorption bands. No detectable changes in transmission were observed after annealing R1 and R7 control glass samples for 24 h at 200 ◦C. Annealing for 24 at 350 ◦C does not change the transmission of R1. For R7 a weak band with amplitude of 0.3cm−1 at 275 unappeased. This effect can be tentatively attributed to thermally-stimulated charge transfer between Ce and Fe ions. However, the amplitude of this thermally induced band is significantly less than the amplitude of bands produced by irradiation.

#### **2.2 Phosphate glass doped with cobalt oxide**

Sodium phosphate glass with different CoO percentage was prepared [El-Batal, 2010], A 60Co gamma cell (2000 Ci) was used as a c- ray source with a dose rate of 1.5 Gy/s (150 rads/s) at a room temperature of 30 C. The investigated glass samples were subjected to

**Gusarov et al (2010)** studied the effect of gamma irradiation on Silica-soda-lime glass with a composition 75SiO2–22Na2O–3CaO, wt.% (labelled R1) and the same glass doped with 0.05 wt.% CeO2 (labelled R7) were melted from high purity raw components using a technology which allowed one to keep the concentration of impurities of Fe ions at a few ppm and other transition metals below 1 ppm. Experimental samples were prepared as plates 25×25mm2, 1mm thick, and polished for optical measurements. The glass samples contained a small number of air bubbles with diameters up to 0.1mm, however transmission measurements at different parts on several samples showed that their influence was below the detection level. All transmission spectra were measured from 195 to 3300 nm with a commercial double-beam UV–Vis–NIR spectrophotometer. Irradiations have been performed in the Brigitte gamma irradiation facility at SCK CEN at 70, 200, and 350 ◦C, 25 kGy/h. They found that the addition ofCeO2 results in significant transmission degradation in the UV (Fig. 6)

Fig. 6. Optical absorption spectra of R1-5 and R7-5 glass samples in the UV range. For each

This degradation is due to the overlapping optical absorption bands of Ce3+ and Ce4+ ions, with maxima at 313 and 240 nm (3.96 and 5.15 eV), respectively [**Arbuzov, 1990**]. Above 350 nm both materials show the same high transmission with no observable optical absorption bands. No detectable changes in transmission were observed after annealing R1 and R7 control glass samples for 24 h at 200 ◦C. Annealing for 24 at 350 ◦C does not change the transmission of R1. For R7 a weak band with amplitude of 0.3cm−1 at 275 unappeased. This effect can be tentatively attributed to thermally-stimulated charge transfer between Ce and Fe ions. However, the amplitude of this thermally induced band is significantly less

Sodium phosphate glass with different CoO percentage was prepared [El-Batal, 2010], A 60Co gamma cell (2000 Ci) was used as a c- ray source with a dose rate of 1.5 Gy/s (150 rads/s) at a room temperature of 30 C. The investigated glass samples were subjected to

glass two spectra are plotted: before and after annealing for 24 h at 350 ◦C

than the amplitude of bands produced by irradiation.

**2.2 Phosphate glass doped with cobalt oxide**

Fig. 7. Absorption spectra of CoO-doped sodium phosphate glasses with constant 0.25% CoO with additional 5% or 10% of Na2O or 5% or 10% P2O5 before and after gamma irradiation.

Glass as Radiation Sensor 593

Lead silicate and borate glasses glasses **[El-Kheshen, A., 2008]** have been extensively studied these last decades mainly because of their presence and importance in a broad range of technological applications. These glasses have been used in the electronic and optical technologies, such as for electron multiplier **[Anderson,1979**], micro-channel plated **[Wiza, 1979]**, non-linear optical and magneto-optical devises **[George, 1999].** Also, high lead silicate

A base lead silicate glass of the chemical composition PbO 60 wt%, SiO2 40 wt% (71.24 PbO mol%, 28.76 SiO2 mol%) was prepared by **[Azooz , 2009]** .Batches containing the base glass composition to which was added 0.1% of one of the 3d-transition metal oxides: TiO2, V2O5, Cr2O3, MnO2, Fe2O3, CoO, NiO or CuO. An Indian 60Co gamma cell (2000 ci) was used as a

Fig. 8. The optical absorption spectra of the parent glass before and after different doses of

Experimental results indicate that the effect of successive gamma irradiation is mainly concentrated in the changes of the intensities of the already observed UV bands which are

glasses can find application as radiation shielding materials **[Friebele, 1991].**

gamma ray source with a dose rate of 1.5Gy s−1.

**2.3 Lead silicate glass**

gamma rays

the same gamma dose every time. Using a Fricke dosimeter, the absorbed dose in water was utilized in terms of dose in glass. No cavity theory corrections were made. Each glass sample was subjected to a total dose of 5 104 Gy (5MR). The UV–visible absorption of glasses containing CoO-doped sodium metaphosphate glasses. The glass containing 0.05% CoO (glass/Co) reveals before gamma irradiation a strong ultraviolet charge transfer absorption with two small peaks at about 205 and 235 nm and the visible spectrum shows a small broad band centered at about 530 nm. On subjecting this glass to successive gamma irradiation, the UV absorption progressively increases with marked splitting to three component peaks at about 205, 275, and 310 nm and followed by subsequent closelyconnected four peaks at about 340, 400, 450, and 500 nm. With glass containing higher concentrations P0.5% CoO), the optical absorption spectra reveal the same strong ultraviolet absorption with two peaks at about 205 and 235 nm and the visible region shows a very broad band increasing in intensity with the increase of CoO content and exhibiting finally three small peaks at about 500, 540, and 595 nm. With continuous gamma irradiation, the absorption spectra reveal numerous connected peaks extending from 205 up to 400 nm exhibiting continuous growth with gamma irradiation and the distinct broad visible absorption is observed to be finally unaffected by progressive irradiation at high CoO content . The rate of increase with the first dose of irradiation is observed to be very high especially in the band at about 500 nm and the optical density is seen to be slowly increased with progressive irradiation.

#### **2.2.1 Condition of cobalt in glass**

Although cobalt can exhibit different oxidation states in many inorganic complexes but in glasses melted under normal atmospheric conditions, cobalt ion exists in the divalent state with two possible coordination forms, namely the octahedral and tetrahedral **[Bates 1962, Bamford 1977, Paul 1990, Aglan 1955**]; The only known ion having the 3d7 configuration is Co2+. Early, **Aglan 1955**, and later other scientists **[El-Batal,2003]** have studied and interpreted the absorption spectra of glasses containing Co2+ in terms of equilibrium between octahedral and tetrahedral coordination forms of Co2+ ions depending on the type and composition of glass and condition of melting. The energy level diagram for d7 system in octahedral coordination predicts that the spectrum of Co2+ in octahedral symmetry will consist essentially of three bands corresponding to spin-allowed transitions 444C5, <sup>4</sup>442 and 4444 (P) together with several weak lines corresponding to spin-forbidden transitions. However, the band corresponding to the transition 4442 is expected to occur only with low intensity as it corresponds to a forbidden two electron jump. **Bates, 1962** has assumed that in low alkali glasses, Co2+ ions are present in octahedral symmetry probably with a rhombic distortion arising from the Jahn– Teller effect.

The energy diagram for d7 system in tetrahedral symmetry predicts that the spectrum of Co2+ in four coordination consists essentially of three bands **[Sreekanth, 1998]** corresponding to the spin-allowed transition 4<sup>4</sup> 45, 4244 and 4245 (P) together with several weak lines and bands corresponding to spin-forbidden transitions. The splitting of the 44 (P) bands has been attributed to L, S interactions (i.e. a departure from Russel–Sanders coupling) which is also quite large in the free ion. The high intensity of the tetrahedrally coordinated band is a consequence of the mixing of the 3d-orbitals with 4Porbitals and ligand orbital **[ElBatal, 2008]**.

the same gamma dose every time. Using a Fricke dosimeter, the absorbed dose in water was utilized in terms of dose in glass. No cavity theory corrections were made. Each glass sample was subjected to a total dose of 5 104 Gy (5MR). The UV–visible absorption of glasses containing CoO-doped sodium metaphosphate glasses. The glass containing 0.05% CoO (glass/Co) reveals before gamma irradiation a strong ultraviolet charge transfer absorption with two small peaks at about 205 and 235 nm and the visible spectrum shows a small broad band centered at about 530 nm. On subjecting this glass to successive gamma irradiation, the UV absorption progressively increases with marked splitting to three component peaks at about 205, 275, and 310 nm and followed by subsequent closelyconnected four peaks at about 340, 400, 450, and 500 nm. With glass containing higher concentrations P0.5% CoO), the optical absorption spectra reveal the same strong ultraviolet absorption with two peaks at about 205 and 235 nm and the visible region shows a very broad band increasing in intensity with the increase of CoO content and exhibiting finally three small peaks at about 500, 540, and 595 nm. With continuous gamma irradiation, the absorption spectra reveal numerous connected peaks extending from 205 up to 400 nm exhibiting continuous growth with gamma irradiation and the distinct broad visible absorption is observed to be finally unaffected by progressive irradiation at high CoO content . The rate of increase with the first dose of irradiation is observed to be very high especially in the band at about 500 nm and the optical density is seen to be slowly increased

Although cobalt can exhibit different oxidation states in many inorganic complexes but in glasses melted under normal atmospheric conditions, cobalt ion exists in the divalent state with two possible coordination forms, namely the octahedral and tetrahedral **[Bates 1962, Bamford 1977, Paul 1990, Aglan 1955**]; The only known ion having the 3d7 configuration is Co2+. Early, **Aglan 1955**, and later other scientists **[El-Batal,2003]** have studied and interpreted the absorption spectra of glasses containing Co2+ in terms of equilibrium between octahedral and tetrahedral coordination forms of Co2+ ions depending on the type and composition of glass and condition of melting. The energy level diagram for d7 system in octahedral coordination predicts that the spectrum of Co2+ in octahedral symmetry will consist essentially of three bands corresponding to spin-allowed transitions 444C5, <sup>4</sup>442 and 4444 (P) together with several weak lines corresponding to spin-forbidden transitions. However, the band corresponding to the transition 4442 is expected to occur only with low intensity as it corresponds to a forbidden two electron jump. **Bates, 1962** has assumed that in low alkali glasses, Co2+ ions are present in octahedral symmetry probably

The energy diagram for d7 system in tetrahedral symmetry predicts that the spectrum of Co2+ in four coordination consists essentially of three bands **[Sreekanth, 1998]** corresponding to the spin-allowed transition 4<sup>4</sup> 45, 4244 and 4245 (P) together with several weak lines and bands corresponding to spin-forbidden transitions. The splitting of the 44 (P) bands has been attributed to L, S interactions (i.e. a departure from Russel–Sanders coupling) which is also quite large in the free ion. The high intensity of the tetrahedrally coordinated band is a consequence of the mixing of the 3d-orbitals with 4P-

with progressive irradiation.

**2.2.1 Condition of cobalt in glass**

with a rhombic distortion arising from the Jahn– Teller effect.

orbitals and ligand orbital **[ElBatal, 2008]**.

#### **2.3 Lead silicate glass**

Lead silicate and borate glasses glasses **[El-Kheshen, A., 2008]** have been extensively studied these last decades mainly because of their presence and importance in a broad range of technological applications. These glasses have been used in the electronic and optical technologies, such as for electron multiplier **[Anderson,1979**], micro-channel plated **[Wiza, 1979]**, non-linear optical and magneto-optical devises **[George, 1999].** Also, high lead silicate glasses can find application as radiation shielding materials **[Friebele, 1991].**

A base lead silicate glass of the chemical composition PbO 60 wt%, SiO2 40 wt% (71.24 PbO mol%, 28.76 SiO2 mol%) was prepared by **[Azooz , 2009]** .Batches containing the base glass composition to which was added 0.1% of one of the 3d-transition metal oxides: TiO2, V2O5, Cr2O3, MnO2, Fe2O3, CoO, NiO or CuO. An Indian 60Co gamma cell (2000 ci) was used as a gamma ray source with a dose rate of 1.5Gy s−1.

Fig. 8. The optical absorption spectra of the parent glass before and after different doses of gamma rays

Experimental results indicate that the effect of successive gamma irradiation is mainly concentrated in the changes of the intensities of the already observed UV bands which are

Glass as Radiation Sensor 595

Fig. 9. The optical absorption spectra of the Cr-doped lead silicate glasses before and after

Glass is particularly susceptible to radiation-induced coloration/ discoloration due to its amorphous, non-crystalline structure. The nature of the optical changes varies, but usually consists of coloration in the visible light region and the formation of absorption bands in the infrared and/or ultraviolet regions. The optical density is almost always increased. It is well documented, for example, that high doses of gamma radiation turn glass various shades ranging from deep brown to pale amber **[Prasil, 1991].** Clear glass discolors when exposed to gamma irradiation, such as from a Cobalt-60 source. Ordinary flint, borosilicate, and lead glass undergo a color change from clear to light amber, brownish to black, depending on the amount of energy absorbed. Milk glass, when exposed to gamma irradiation, yields a grayish color, depending on energy absorbed and any swirling effect is highlighted, probably due to concentrations of color in the glass that have not mixed uniformly. The actual mechanism of the formation of "color centers" has been described **[Prasil, 1991].** The final color created is dependent on the chemical composition of the glass and can be altered by selection of additives (e.g., cerium ions can reduce browning; manganese ions induce an

**2.4 Radiation processing for glass coloration / discoloration**

different doses of gamma rays.

assumed to be due to trace iron impurities (mainly Fe3+ ions) and to the Pb2+ ions. The main pronounced difference is the sharp growth of the kink at about 390nmto a pronounced peak and the quite resolution of a broad visible band centered at about 500 nm. It seems that the presence of high content of the heavy metal oxide (PbO), shows some shielding towards successive gamma irradiation and only limited changes are observed. This behavior is related to the presence of heavy Pb2+ ions which retard the movement or transfer of released electrons during the irradiation process **[Singh, 2004]**.