Isotope persisted down to the present because their rate of decay is so slow (e.g. uranium-238 and potassium-40). Post-primordial isotopes were created by cosmic ray bombardment as cosmogenic nuclides (e.g., tritium, carbon-14), or by the decay of a radioactive primordial isotope to a radioactive radiogenic nuclide daughter (e.g. uranium to radium). A few isotopes are naturally synthesized as nucleogenic nuclides, by some other natural nuclear reaction, such as when neutrons from natural nuclear fission are absorbed by another atom. As discussed above, only 80 elements have any stable isotopes, and 26 of these have only one stable isotope. Thus, about two-thirds
High Flux Isotope Reactor monitoring and enables individual inspectors to obtain large numbers of samples in the hopes of finding required evidence. By screening those samples, the very high costs of destructive analysis are required only for those samples deemed interesting. Delayed neutron analysis is becoming increasingly useful for these studies. A recent application involves the irradiation of programmable memory devices that have been coated with a small amount of a fissile isotope. The fission events induced upon irradiation may be tracked spatially by comparing the values in memory with those assigned to memory initially; areas of differences are attributed to damage caused by