Analysis of the possibilities of the neutron-resonance method of determining the elemental composition of matter

Abstract

Mathematical modeling of the neutron-resonance method analyzing the elemental and isotopic of matter is performed. The method is based on investigation of γ cascades, emitted by nuclei as a result of the radiative capture of neutrons. Gamma cascades of the determined element (effect) and elements of the matrix (background) are modeled and these cascades are detected with a γ-ray multisectional 4π detector. The response functions of the detector are presented for the case of an analysis of the gold content in a natural medium. It is shown that the introduction, performing together with neutron spectrometry, the spectrometry of γ cascades makes it possible to increase the effect/background ratio by a factor of 100. It is noted that this ratio can be further increased by improving the method used to detect γ cascades and analyzing the results of the measurements.A method for analyzing the elemental and isotopic composition of matter on the basis of determining the neutron resonances of the desired elements by measuring the distribution of the number of γ rays [3] or in general the spectrum of γ cascades [4], emitted as a result of radiative capture, as a function of the neutron energy is examined in [1,2]. This method can be effectively used to determine elements whose nucleus contains resonances at low neutron energy. It is highly sensitive and fast because the multidimensional energy spectrum of γ cascades and neutron energy spectrum are measured simultaneously, the high fluxes of resonance neutrons at low energy, and almost 100% γ-cascade detection efficiency.In the present work, the method is modeled mathematically for the purpose determining ways to improve is for the example of determining the gold concentration in an ore sample.The main factor making possible to determine the desired element or isotope is related with the determination of its neutron resonance by measuring the neutron energy spectrum. This is because the cross section for radiative capture is much greater than the corresponding cross sections of other matrix elements. Thus, the cross section for radiative capture at the resonance of gold (the element being determined) at neutron energy E n = 4.91 eV is ~3·10 4 b, which is more than 10000 times greater than the cross section for the nuclei of the elements in the matrix (back-ground forming elements). This makes it possible to intensify the effect due to gold by the same factor. The effect/background ratio can be estimated from data on the neutron cross sections and the content of various elements in the sample being analyzed (specimen).We shall examine this for case of analysis of a gold-containing sample from the Sukhoi Log mine. Table 1 gives the radiative capture cross sections σ γ at energy E n = 4.91 eV for the main background-forming elements in the matrix of the sample and the number n of nuclei and the probability of radiative capture P γ calculated for 1 g of the matrix material. The data for gold, corresponding to its concentration C = 1 g/ton, are presented for comparison. The proba...