Geiger counter and its control unit

TOPIC: NUMBER: LAB SESSION: COURSE: DATE: AIM/OBJECTIVES:1. To determine the concept of radioactivity and the random nature of the process2. Familiarize ourselves with the exposure methods3. To the effect of ionization radiation on the health of humans4. To determine the optimum operating voltage of the Geiger Muller5. Measures the background countTHEORY: The Geiger counter is simply a detector filled with a gas, which produces some sort of impulses, which may be counted electronically. The Geiger relies on the ionization effect to produce the impulse. An incoming particle produces free charge in the sensitive volume of the detector via the process of ionization of gas atoms. Due to the charge creation, the free charges are swept up. This current pulse causes a momentary potential difference to appear, which is detected, amplified by the amplifier and counted by the electronics of the system. The behavior of the system is affected by the magnitude of the potential difference applied between the anode and the cathode. The behavior is illustrated inform of a curve of pulse height against applied voltage. EQUIPMENTS:1. Geiger counter and its controlling unit2. Sealed radioactive sources3. Sample holder4. Tweezers5. Lead bricks for shieldingPROCEDURE:Determination of operating voltage of a Geiger counter1. The EHT was given about 5 minutes to warm up after putting it on.2. Place a radioactive source in a stable position in the holder below the Geiger tube window and approximately 2-3cm away from the window.3. Slowly the EHT was increased until the system starts to count. This was referred to as threshold voltage4. The record of count rate vs. EHT was taken5. The midpoint of the reading’s plateau was selected as the operating point.Determination of the slope of the Geiger plateauUsing the count rate C1 (beginning of the plateau) and the count rate C2 (almost 100 to 10 volts beyond C1). Both count rates were allocated operating voltages V1 and V2 respectively. The values of V and C were used to determine the slope of the plateau using an equation.Determination of counter Dead TimeOnce the system is set up in an optimum condition, source 1 is placed on the split holder and the number of count rates per second is measured as N1. While the source is still in place, source 2 is placed in the holder and the equivalent count rate per second taken, as N12. Source 1 is now removed and the number of count rates per second is taken as N2. Finally, this can be used to calculate the dead time. RESULTS:EHT (+_)COUNTU(+_)COUNT RATE(+_)U800237191547917.75188402543981598708.3588027459165902839920291501709568.739603058217410109.0810003139517710199.1011003441018511159.12120060815246210615.4710803198117810379.22114035373188116210.12The figure below shows a scatter plot graph that demonstrates the relation between EHT (volt) and the Count Rate. From the results above, the slope of the graph is obtained by: Difference between EHT/Difference between the count rateDISCUSSION:The slope and the percentage slope of the curve can also be worked out from the count rates. The period of time, during and immediately following an ionization event, when the system is insensitive to a further radiation, is referred to as the Dead time. After placing the material in the holder and setting the voltage to a certain value, we stills didn’t record any count rate until we attained a certain value of EHT. This is because the energy is very low below that point to be able to separate them very fast. On the other hand, the behavior of the system depended on magnitude of the potential difference applied between the anode and the cathode.CONCLUSION:Radioactive material can be used to determine the operating voltage of the Geiger counter, the slope percentage of the plateau and the dead time of the counter. This simply involves radioactive material and recording its EHT and counts rate at a certain amount of time.ASSIGNMENT:What produces the background count measures?The count measure occurs due to the radiation released and emitted by the material in the holder. When a specimen or material is in exited state, it means that it has absorbed radiation of a quantized amount. When the sources are cleared off the bench, the exited specimen will emit radiation to return to the ground level Effects if all results of background were collectedCollecting all the values will add errors to the results because the atom may undergo other reaction in the atmosphere which may result in absorption or emission of a radiation.Why is the dead time correction significant at high count rate but not at low count rate?This is because dead time occurs at very high ionization and high counts but not at low counts.Can a Geiger counter be used to determine the energy of the x-ray photons?Yes. At the x-ray region, there is a characteristic of high energy and low wavelength. The energy is used to change the vibration of molecules and determine their identity. A Geiger counter is characterized by high energy in the region of x-ray.BibliographyCurtain University of Technology Laboratory Manual: Medical Physics 161(26-31)