The influence of anisotropic electron drift velocity on the signal shapes of closed-end HPGe detectors
The influence of anisotropic electron drift velocity on the signal shapes of closed-end HPGe detectors
复制标题
各向异性电子漂移速度对封闭式 HPGe 探测器信号形状的影响
DOI：
10.1016/s0168-9002(99)01286-3
复制
发表时间：
2000
影响因子：
1.4
通讯作者：
H. Jäger
中科院分区：
文献类型：
--
作者：
L. Mihailescu;W. Gast;R. Lieder;H. Brands;H. Jäger
本研究关注高电场和低温下锗晶体中电子漂移速度的各向异性，及其对封闭式同轴几何形状的 n 型高纯锗 (HPGe) 探测器中电荷收集过程的影响。使用唯象模型模拟 HPGe 探测器内的电子轨迹，以计算漂移速度对电场和晶体取向之间角度的依赖性。将给定探测器几何形状和前置放大器带宽产生的感应电流和脉冲形状与实验进行比较。通过实验，观察到封闭端 HPGe 探测器中脉冲形状对电导率各向异性的依赖性。脉冲形状的实验数据是通过对封装的六角形EUROBALL探测器的前置放大器信号进行采样获得的，该探测器由准直22Na和241Am源照射。通过中子反射测量晶体取向。模拟脉冲形状与实验脉冲形状之间存在定性一致性。对于载流子相对于晶体取向的不同漂移方向，观察到电荷收集时间的变化高达 50ns。此外，通过模拟预测轨迹与直线径向漂移方向的偏转约为 20°。同轴Ge探测器中载流子漂移速度各向异性的这两个主要效应预计将在γ射线跟踪探测器的发展中发挥重要作用。
This study is concerned with the anisotropy of the electron drift velocity in germanium crystals at high electric fields and low temperature, and its influence on the charge collection process in n-type, high-purity germanium (HPGe) detectors of closed-end, coaxial geometry. The electron trajectories inside HPGe detectors are simulated using a phenomenological model to calculate the dependence of the drift velocity on the angle between the electric field and the crystal orientation. The resulting induced currents and pulse shapes for a given detector geometry and preamplifier bandwidth are compared to experiment. Experimentally, the dependence of the pulse shapes on the conductivity anisotropy in closed-end HPGe detectors was observed. The experimental data on pulse shapes were obtained by sampling preamplifier signals of an encapsulated, hexaconical EUROBALL detector, which was irradiated by collimated22Na and241Am sources. The crystal orientation was measured by neutron reflection. Qualitative agreement between the simulated and experimental pulse shapes was found. A variation in the charge collection time of up to 50ns was observed for different drift directions of the carriers relative to the crystal orientation. Furthermore, a deflection of the trajectories from a straight radial drift direction of about 20° was predicted by the simulations. These two main effects of charge carrier drift velocity anisotropy in coaxial Ge detectors are expected to play an important role in the development of γ-ray tracking detectors.