低能康普顿散射模拟模型在高纯锗探测器中的研究

The research of low energy compton scattering model in simulation by high purity germanium detector

摘要:

国际上CDEX、CDMSlite等实验组，在开展直接暗物质探测实验中，发现高能光子本底的来源之一. 高能光子在高纯锗探测器中会产生低能本底，这些本底来自于康普顿散射的影响. 分析发现低能本底的结构有台阶出现，这与经典理论预测的结果相悖. 这是由于原子中电子处于束缚状态，并具有一定的动量，因此康普顿散射在低能部分受到影响. 现在已经有低能康普顿散射理论Impulse Approximation(IA)考虑到电子的这些效应，并且应用到模拟实验软件Geant4中. IA理论框架下的模拟模型有三个: Liermore模型、Penelope模型和Monash模型. 我们发现三个模型在keV能级以下能谱有康普顿台阶出现，与经典康普顿能谱相比有明显减少. 经过计算，在k壳层的台阶高度比例分别为95.92%、92.87%和96.68%，这与只考虑束缚效应而计算出的93.73%不同. 三个模型keV能级以下时有大约10%的差异.

Abstract:

Direct dark matter detection experiments such like CDEX, CDMSlite collaborations pursue the searches with germanium detectors at low energy region. Measurements indicate one of the main background sources is originated from high energy gammas through Compton scattering and its spectra appears the step structures at electronic orbital energies. The result has contradiction with classical Compton model. In reality, high energy gammas interact with the bound electrons in atoms in terrestrial detectors. The low energy Compton scattering theory is depended on impulse Approximation framework. This work aims at low energy spectra via atomic Compton scattering models in Geant4 software. The work has been carried out the comparison of Livermore model, Penelope model as well as Monash model in the simulation framework. The ratios of the step structure at K-shell are 95.92%, 92.87%, 96.68%, respectively, which reflects the bound electron effect. Spectra at sub-keV energy region demonstrates a 10% discrepancy among those models.