Pulsed-Neutron Activation Analysis System for Short-Lived Radioisotopes

A pulsed-neutron activation analysis system capable of handling and analyzing short-lived radioisotopes with half-lives as short as 1 to 2 sec was developed. Since a single reactor pulse will induce more activity for short-lived neutron reaction products than continuous irradiation to saturation at a normal reactor power level, experimental procedures were formulated to analyze quantitatively a few important fast neutron reactions with short-lived products and to establish limits of detection for these reactions using this system. To augment the fast neutron reactions, a cadmium-lined in-core terminus was utilized to reduce (n,γ) interference reactions.

The reactions analyzed were ¹⁶O(n,ρ)^l6N,¹⁹F(n,α)¹⁶N, ¹⁹F(n,γ)²⁰F, ²³Na(n,ρ)²³Ne, ²³Na(n,α)²⁰F,³⁴S(n,ρ)³⁴P, and ³¹P(n,α)²⁸Al. The detection limits which were attained for these reactions utilizing this system were: 54.8 µg for ¹⁶O, 0.23 and 0.19 µg for ¹⁹F, 1.8 and 8.0µg for ²³Na, 150 µg for ³⁴S, and 2.6 µg for ³¹P. Most of these limits are an order of magnitude or more lower than those reported by users of the Cockroft-Walton neutron generators usually employed for these analyses.