Scope1.1 This test method covers the measurement of reaction rates by determining the amount of the fission product 99 Mo produced by the non-threshold reactions 241 Am(n,f), 235 U(n,f), and 239 Pu(n,f) and by the threshold reactions 238 U(n,f), 237 Np(n,f), and 232 Th(n,f). 1.2 These reactions produce many fission products, among which is 99 Mo, having a half-life of 65.94 h. Because of unresolved or interfering gamma rays when gamma-ray spectrometry is accomplished, the competing activity from other fission products requires that a chemical separation be employed to isolate the 99 Mo. 99 Mo emits gamma rays of several energies, which are easily detected and identified by a gamma-ray spectrometer. 1.3 With suitable techniques, neutron fluence rates can be measured in the range 10 to approximately 10 14 n[dot]cm [dot]s . 1.4 The measurement of time-integrated reaction rates with fission dosimeters by 99 Mo analysis is limited by the half-life of Mo to irradiation times up to about 300 h. 1.5 The values stated in SI units are to be regarded as the standard. 1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
