Reaction Gammas for Analysis of Impurities in Alpha Emitters

Certain light elements that undergo nuclear reactions with alpha particles can be identified in alpha emitters such as ²³⁸PuO₂ by analysis of the resulting radiation—specifically, of gamma photons, or “reaction gammas.” Gamma spectrometry has been used successfully for this purpose on production lots of ²³⁸PuO₂ from which neutron emission rates were abnormally high because of (α,n) reactions with impurities. To establish a base for this type of analysis, reaction gamma spectra for 14 light elements were obtained by measuring gamma spectra from samples of ²³⁸PuO₂ before and after addition of known quantities of the elements. Emission rates of major gammas of each element, in γ/min per gram of ²³⁸Pu, were also developed from these standard mixtures. A catalog of principal reaction gammas from each element was assembled. Although absolute emission rates of reaction gammas were obtained, this technique is only semiquantitative because the gamma yield is highly dependent on a number of variables, including the incident alpha-particle energy and the distribution of the impurity element in the sample.