ASTM E393-96

1.1 This test method describes two procedures for the measurement of reaction rates by determining the amount of the fission product Ba produced by the non-threshold reactions 235 U (n, f), 241 Am (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 140 Ba, having a half-life of 12.752 days. 140 Ba emits gamma rays of several energies; however, these are not easily detected in the presence of other fission products. Competing activity from other fission products requires that a chemical separation be employed or that the Ba activity be determined indirectly by counting its daughter product La. This test method describes both procedure (a), the nondestructive determination of Ba by the direct counting of La several days after irradiation, and procedure (b), the chemical separation of Ba and the subsequent counting of Ba or its daughter 140 La.

1.3 With suitable techniques, fission neutron fluence rates can be measured in the range from 10 n (neutrons) [dot]cm -2 [dot]s -1 to approximately 10 15 n[dot]cm -2 [dot]s -1 .

1.4 The measurement of time-integrated reaction rates with fission dosimeters by Ba analysis is limited by the half-life of 140 Ba to irradiation times up to about six weeks.

1.5 The values stated in SI units are to be regarded as 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.