溴化镧探测器γ射线能量展宽及解谱研究

Study of Energy Broadening and Spectrum Unfolding for Lanthanum Bromide Detector

溴化镧(LaBr_(3):Ce)探测器是一种性能优良的无机闪烁体探测器,准确的LaBr_(3):Ce探测器γ响应参数以及响应能谱是开展应用工作的基础。通过对实验中实测γ能谱的分析,可以得到溴化镧谱仪的半高宽-能量关系,在尝试使用MCNP中GEB卡还原此关系时,发现可将程序中自带的半高宽-能量函数简化,简化后的函数关系仍能较好地反映实验测量信息。在此基础上,采用MCNP程序模拟了0.1~5 MeV的单能γ射线在Φ50 mm×10 mm溴化镧探测器中的响应输出,构建了其γ响应函数矩阵。通过能谱计算得到展宽系数后,编写MATLAB计算程序对构建的响应矩阵进行高斯展宽。利用展宽后的矩阵通过加权最小二乘法对实验测得的复杂能谱进行解谱,并将解谱结果与实验测量数据进行比较验证。结果表明:展宽后的响应函数与实验得到的响应函数符合一致,通过数值解谱可以很好地给出实验测量中不同γ源的能量以及相对产额等信息。

Lanthanum bromide(LaBr_(3):Ce)detector is a kind of newly developing inorganic scintillator detector,which has high resolution and can be made into larg size.The LaBr_(3)scintillator detector used in this experiment is provided by Northwest Nuclear Technology Research Institute.The detector is composed of cylindrical LaBr_(3):Ce crystal(50 mm in diameter and 10 mm in thickness)and 9815B photomultiplier tube produced by ET Company.It was calibrated with standard Co,Cs,Eu source to verify its energy linearity.The lanthanum bromide detector used in the experiment was simulated by MCNP software package.The GEB card in MCNP can broaden simulated energy spectrum with its own FWHM-energy function.When using the GEB card to reproduce experiment spectrum,it's found that the function GEB card carries can be simplified.It can be converted from a three parameter function to a two parameter function.Using the new function to simulate spectrum,it can be seen that the simulated energy spectrum can reproduce the experimental energy spectrum well.Attempt of using this function to try to unfold the spectrum for verifying the correctness and practicability of this function was also made.Taking 0.1 MeV as the starting point,0.05 MeV as the step,5 MeV as the energy end point,99 single energy-ray response are simulated using MCNP.The MATLAB calculation program is compiled using the simplified function to expand the response matrix to Gaussian.The broadened matrix is used to unfold the spectrum through the weighted least square method.By weighting the energy channels with different counts,the contribution of important signals with more counts(such as full energy peak)to spectrum unfolding can be improved,which can effectively improve the accuracy of spectrum solution and ensure the correctness of spectrum unfolding.The background spectrum and coCo spectrum are unfolded.The background of the detector mainly comes from two kinds of rays.There are two kinds of gamma rays emited from the decay of 138 La.For one,13 La is converted from electron capture to 138Ba,and then 138Ba in the excited state de-excite to emit-rays with energy corresponding to 1,436 keV.This kind of-rays combine with the X-rays with energy corresponding to 32 keV by K-electron capture results in a sum peak corresponding to 1,467.7 keV.The other gamma ray is emited by 13La throughβ~decay with energy corresponding to 788.7 keV,branch ratio of this gamma ray is 34.4%.The results are verified with the experimental results.The calculated results show that the response function after broadening is basically consistent with the response function obtained from the experiment,and the energy and relative yield information of the source in the experiment can be obtained by unfolding the spectrum.