Epithermal neutron activation analysis of short-lived radionuclides using a pneumatic transport system and a pulsed D-T neutron generator

A pneumatic transport system for the detection and characterization of short-lived (of order 60 s or less) radionuclides produced during irradiation by a D-T neutron generator was constructed. Target samples of indium, palladium, and germanium were irradiated by the neutron generator embedded in a graphite monolith to produce epithermal activation products. The three radioisotopes of interest are palladium-107, palladium-109, and germanium-75. The experimental half-lives of each of the three isotopes, with the specific activity in parenthesis are: 21.82±3.71 (49.36 nCi/g), 279.21±27.80 (158.91 nCi/g), and 48.51±12.58 (504.78 nCi/g) respectively. These experimental half-lives agree with the published half-lives. The Monte Carlo N-Particle (MCNP) radiation transport code was used to model the graphite pile, the pneumatic transport tube, and the neutron generator. This resulted in benchmarking and validation of the experimental results. In order to reach an agreement between the experimental results and MCNP, a modification was required to the neutron absorption reaction rate produced from MCNP using isomeric to ground state ratios to accurately account for the decay mode most common with these short-lived radioisotopes