ASTM E 393 : 1996 : R2002

1.1 This test method describes two procedures for the measurement of reaction rates by determining the amount of the fission product ¹⁴⁰Ba produced by the non-threshold reactions ²³⁵U (n, f), ²⁴¹Am (n, f), and ²³⁹Pu (n, f), and by the threshold reactions ²³⁸U (n, f), ²³⁷Np (n, f), and ²³²Th (n, f).

1.2 These reactions produce many fission products, among which is ¹⁴⁰Ba, having a half-life of 12.752 days. ¹⁴⁰Ba 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 ¹⁴⁰Ba activity be determined indirectly by counting its daughter product ¹⁴⁰La. This test method describes both procedure (a), the nondestructive determination of ¹⁴⁰Ba by the direct counting of ¹⁴⁰La several days after irradiation, and procedure (b), the chemical separation of ¹⁴⁰Ba and the subsequent counting of ¹⁴⁰Ba or its daughter ¹⁴⁰La.

1.3 With suitable techniques, fission neutron fluence rates can be measured in the range from 10⁷ n (neutrons) cm² s¹ to approximately 10 ¹⁵ n cm² s¹.

1.4 The measurement of time-integrated reaction rates with fission dosimeters by ¹⁴⁰Ba analysis is limited by the half-life of ¹⁴⁰Ba 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.