Characterization and use of the new NIST rapid pneumatic tube irradiation facility

Abstract

Recently a new rapid pneumatic tube facility was inserted into a long unused location in the NIST 20 MW nuclear reactor. This facility was designed and constructed specifically for rapid INAA using short lived activation products. Included is a computer controlled console which uses fast sensors to accurately measure the irradiation capsule flight time, and a loss-free counting system connected to a 32% efficient HPGe detector with a transistor reset preamplifier. Measurement of travel times from end-of-irradiation to detector were 473±8 ms. Measurement of the thermal neutron fluence rate was 5.0·1013 n·cm-2·s-1. The other three pneumatic tubes in the NIST reactor have transfer times of 3 to 15 seconds, and no timing capability more accurate than human response. This new facility substantially improves our ability to accurately determine activation products with half-lives from 1 to 100 seconds. Characterization information reported on this new irradiation facility includes absolute fluence measurements, fluence rate variations within the capsule and variations with time, and determination of analytical sensitivities for fluorine-20, selenium-77m, and silver-110g.