Sensitivity Study Of Underwater γ Energy Spectrometerbased On Nal Detector

Radioactivity in the ocean is at a low or very low level,which puts forward high requirements for the sensitivity of radioactive measurement equipment.The main factor affecting the sensitivity of measurement equipment is the detection efficiency,the Monte Carlo method is used in this paper to investigate the performance of underwater gamma ray spectrometers based on sodium iodide detectorsγthe relationship between the sensitivity of an energy spectrometer and the sensitive volume of the detected crystal was systematically studied.Since the lower detection limit only characterizes the ability of the measuring instrument to qualitatively determine the presence or absence of radionuclides in the medium,while the measurement accuracy characterizes the ability of the measuring instrument to quantitatively measure radionuclides.This indicator also determines the detection efficiency and crystal sensitive volume of the instrument.As an important basis for the design of underwater detector crystals,this article also discusses the underwater detector crystal designγthe relationship between the measurement accuracy of an energy spectrometer and the sensitive volume of the detected crystal was studied.The main research content of this article are as follows:1)Study the geometric model of the detector simulation.Compare the detection efficiency and peak to total ratio of the detector obtained by building the model with the actual measurement results,thereby improving the model;2)The effective detection distance of the detector.Select four different energies of 364.49 ke V,662.00 ke V,1460.82 ke V,and 2614.50 ke VγSimulate and calculate the variation of the full energy peak to peak ratio counting rate with the radius of the simulated water body,in order to determine that the effective detection distance of the detector should be at least 0.7 m,providing a theoretical basis for the deployment of detectors in practical water monitoring applications,and determining the radius of the simulated water body for subsequent calculations;3)The minimum detectable activity concentration of the detector.Using the Monte Carlo method,based on the simulation of sodium iodide detectors,the energy spectra of various single crystal volumes and polycrystalline arrays are obtained,and the background and net counting rates of various radionuclides such as ¹³⁷Cs,¹³¹I,⁶⁰Co,²⁰⁸Tl,and ⁴⁰K are calculated to obtain the minimum detectable activity concentration at different measurement times,thereby qualitatively analyzing the relationship between the crystal volume,layout,and sensitivity of underwater Na I（Tl）detectors.4)Study the relative standard deviation of the detector.Use a Na I（Tl）detector to obtain the energy spectrum of various radionuclides,and calculate their background counting rate and net counting rate to obtain the relative standard deviation,thereby quantitatively analyzing the relationship between the crystal volume and arrangement of underwater Na I（Tl）detectors and their sensitivity.