Influence And Modification Of Mass Sample Thickness On Quantitative Analysis Of Neutron Activation

Compared with the traditional neutron activation analysis method,there are some problems in the irradiation and measurement process of large mass samples.These problems include the change of neutron flux and energy in the sample,the neutron self-shielding effect of the irradiation process,and the influence of the gamma-ray self-shielding effect in the measurement process.Therefore,the neutron activation analysis of mass samples needs to be modified.Flour mainly contains C,H,O,N,Ca,F and other elements,talc powder is the main chemical composition of Mg₃[Si₄0₁₀]?OH?₂.Therefore,it is possible to determine whether the flour contains talc powder and its exact content by measuring the content of silicon and magnesium elements.In this paper,the influence and correction of the thickness of large mass samples on the quantitative analysis of neutron activation are studied by combining the simulation and experimental measurement of MCNP5?Monte Carlo N–Particle Transport Code System5?.1.The relationship between neutron flux and neutron energy and the thickness of flour samples was simulated by using MCNP5,and the neutron flux at different thicknesses of flour samples was measured experimentally by helium 3 proportional counting tube,and the results showed that the MCNP5 simulation results were basically consistent with the experimental results.2.Using MCNP5 to simulate 14 MeV neutron activation analysis of flour samples,based on the simulation results,the relationship between the characteristic energy gamma ray intensity and the sample thickness produced by neutron activation of radionuclide ²⁴Na and ²⁸Al in ²⁴Mg and ²⁸Si nuclei was studied,and the self-absorption effect of gamma rays in flour samples was analyzed.3.Preparation of talc samples containing different content,using D-T neutron generator as neutron source for neutron activation analysis of flour samples.The slow-onset gamma energy spectra of flour samples with different thicknesses after neutron irradiation were measured,and the gamma energy spectra obtained by the experiment were analyzed by spectrum.Under experimental conditions,the relationship between the characteristic energy gamma ray intensity and the sample thickness produced by the production of radionuclide ²⁴Na and ²⁸Al decay by neutron activation of ²⁴Mg and ²⁸Si nuclei was obtained.4.Through experimental measurement and MCNP5 simulation,the optimum experimental conditions for the sample thickness of 6.6 cm for neutron activation analysis of flour samples were finally determined.According to the simulation results,the relationship between the characteristic gamma-ray count and the sample thickness is given,and the results are in good agreement with the experimental comparison.