Standard Test Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of Niobium

1.1 This test method describes procedures for measuring reaction rates by the activation reaction ⁹³Nb(n,n) ^93mNb.

1.2 This activation reaction is useful for monitoring neutrons with energies above approximately 0.5 MeV and for irradiation times up to about 30 years.

1.3 With suitable techniques, fast-neutron reaction rates for neutrons with energy distribution similar to fission neutrons can be determined in fast-neutron fluences above about 10¹⁶cm ². In the presence of high thermal-neutron fluence rates (>10 ¹²cm²·s^-1), the transmutation of ^93mNb due to neutron capture should be investigated. In the presence of high-energy neutron spectra such as are associated with fusion and spallation sources, the transmutation of ^93mNb by reactions such as (n,2n) may occur and should be investigated.

1.4 Procedures for other fast-neutron monitors are referenced in Practice E 261.

1.5 Fast-neutron fluence rates can be determined from the reaction rates provided that the appropriate cross section information is available to meet the accuracy requirements.

1.6 The values stated in SI units are to be regarded as the standard.

1.7 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.