论文标题
$^{210} $ pb在NAI（TL）水晶表面的深度概况研究
Depth profile study of $^{210}$Pb in the surface of an NaI(Tl) crystal
论文作者
论文摘要
表面$^{210} $ pb是使用NAI（TL）晶体进行深色搜索实验的主要背景来源之一，其光谱特征与beta-decay事件相关的beta-decay事件小于60 keV取决于$^{210} $ pb的深度分布在NAI（TL）水晶的表面中。因此，我们必须了解使用NAI（TL）晶体的低能地面实验的低能区域中的表面$^{210} $ Pb的曲线。我们通过建模$^{210} $ po的α衰减，以表面$^{210} $ pb污染的衰减顺序对α排放的测量光谱进行建模，从而估计表面$^{210} $ pb污染的深度曲线。为了描述表面污染的能量光谱，我们对测量数据的对数似然拟合到Geant4 Mote Carlo模拟的总和，并由指数曲线加权，这是表面深度的函数。还对表面$^{210} $ PB的β衰减中的低能和高能事件进行了建模，以改善浅深度的深度曲线。我们通过遵循两个指数函数在表面上呈指数分布的$^{210} $ pb的β衰减的能量光谱，其中均值深度系数是数据拟合中的免费参数；我们观察到能量光谱与测量数据非常吻合。
The surface $^{210}$Pb is one of the main background sources for dark-matter-search experiments using NaI(Tl) crystals, and its spectral features associated with the beta-decay events for energies less than 60 keV depends on the depth distribution of $^{210}$Pb in the surface of an NaI(Tl) crystal. Therefore, we must understand the profile of surface $^{210}$Pb to precisely model the background measurement in the low-energy region for the low-background experiment using NaI(Tl) crystals. We estimate the depth profile of the surface $^{210}$Pb contamination by modeling the measured spectrum of the alpha emission from the decay of $^{210}$Po at the decay sequence of the surface $^{210}$Pb contamination that is obtained using an $^{222}$Rn-contaminated crystal. In order to describe the energy spectra of the surface contamination we perform a log-likelihood fit of the measured data to a sum of Geant4 Mote Carlo simulations, weighted by an exponential curve as a function of the surface depth. The low- and high-energy events from the beta decay of surface $^{210}$Pb are also modeled to improve the depth profile for shallow depths. We simulate the energy spectra from beta decays of $^{210}$Pb that are exponentially distributed in the surface by following two exponential functions where the mean-depth coefficients are free parameters in the data fitting; we observed that the energy spectra are in good agreement with the measured data.
