Acquisition Of Elemental Standard Spectrum In Pulsed Neutron Spectroscopy Logging

All energy spectrum quantitative analysis methods assume that the measured mixed spectrum of the instrument is a linear superposition of the standard spectrum of each element,and the accurate and effective standard spectrum is the basis for determining the dry weight of the elements and the mineral content in geochemical elemental logging.There is a lot of space for improvement in the accuracy and validity of the standard spectrum.Therefore,it is necessary to carry out research on the acquisition of controlled source geochemical elemental logging standard spectra.In this paper,Monte Carlo numerical simulation program MCNP is used to simulate the capture standard spectrum of 16 elements and the inelastic standard spectrum of 9 elements.When the detection crystal is LaBr₃,the continuation algorithm,the increase weight window,and the importance of cells are used in optimization.In order to verify the validity of the standard spectrum and the effectiveness of optimization methods,a variety of simple and complex formation models were established to obtain the capture spectra of each mixed formation.The former standard spectrum and the optimized standard spectrum are used to solute spectra of these mixed formations to obtain the yield of each element.Then the closed model and sensitivity factor are used to convert the yield into the dry weight of the element.The dry weight of the elements obtained by deconstructing the spectrum and the theoretical dry weight of the elements were compared.The results show that:1.Compared with the standard spectrum simulated by other methods,the standard spectrum simulated in this paper has less statistical fluctuations,more prominent characteristic peaks;2.It is important to use continuation algorithms,the increase weight window,and the importance of cells.The optimization of the standard spectrum after the optimization methods such as optimization,accuracy of the spectrum,the calculated element dry weight error is small and not affected by environmental factors;3.The hydrogen index of formation has a great influence on the standard capture spectra of H and Cl elements,therefore,the H and Cl capture standard spectra should be re-simulated when the local hydrogen index changes.