Quantitative Evaluation of Nuclide Density Distribution in a Substance by Neutron Resonance Absorption Transmission Method

Abstract

We can non-destructively obtain an image of nuclide/isotope distribution or temperature in a substance by analyzing the dips due to the resonance absorption in a neutron transmission spectrum. The observed transmission spectra are expressed by convolution of intrinsic resonance cross section and neutron pulse shape, namely the emission time distribution of neutrons emitted from a moderator. Therefore, the pulse shape should be reproduced at arbitrary energy by a synthetic function for performing the quantitative resonance analysis. We have found that the Cole-Windsor function reproduced well the pulse shape of the instrument at J-PARC (Japan Proton Accelerator Research Complex) neutron source and succeeded in evaluating nuclide density of some samples quantitatively by analyzing transmission resonance spectra. On the other hand, the function expressing the pulse shape of a thermal neutron source at Hokkaido University has not been found. Therefore, we have calculated the pulse shape of epithermal neutrons by Monte-Carlo simulation and fitted the pulse shape using several kinds of function. We found that the Cole-Windsor function also was the best function for reproducing the pulse shape of the source. Moreover, we implemented it to the resonance analysis code and calculated the resonance transmission spectra of some nuclide to evaluate the capability for resonance analysis at Hokkaido University source.