Determination of neutron absorption self-shielding factors for lanthanide elements during Neutron Activation Analysis

Kravitz, Isaac Nathan
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Neutron Activation Analysis (NAA) is a non-destructive method of analyzing the elemental composition of a sample with fine detection limits that can reach parts per billion for some isotopes. When conducting NAA, materials with high absorption cross-sections reduce the overall neutron flux within the sample by absorbing incident neutrons. This effect is known as neutron self-shielding. The implementation of correction factors that can account for these effects are important in increasing the precision of NAA. The objective of this research was to determine a wide variety of neutron self-shielding factors for each lanthanide element, with the exception of promethium, for a range of isotopic concentrations. This was done by experimentally irradiating solutions of these elements and using NAA to determine the activity of each sample. The results were then normalized to a standard to determine the self-shielding effects at varying concentrations. The experimentally measured self-shielding factors were then compared to values generated from two computer models to verify the accuracy of the data. With the exception of elements with very large absorption cross-sections, the results of these computer models were shown to be in excellent agreement with the data collected experimentally.