Background Reduction of Cosmic X-ray Detector By Means of High Speed Pulse Shape Processing

研究了X射线计数器输出信号脉冲波形的数字处理技术。我们的第一个动机是比通常的上升时间判别法更有效地减少正比计数器中的粒子背景。然而，在研究过程中，我们注意到可以通过脉冲波形处理(分析)来进行X射线光子的偏振测量。基本的想法是由于这样一个事实，即光电子优先发射到与入射光子的电矢量平行的方向。如果光电子的能量足够高，足以反映其发射方向对初级电子云的伸长，则脉冲形状将取决于发射方向和阳极线之间的几何形状。平均而言，对于具有平行于阳极线的电矢量的X射线光子，输出脉冲上升得比垂直情况下更快。为了检验“脉冲形状(或ri…时间更长)X射线偏振器”的概念，我们在日本筑波高能物理研究所的同步加速器设施中进行了实验。我们在那里对着单色X射线束照射了一个充满Xe的正比计数器。使用数字存储示波器对计数器前置放大器的输出信号进行采样。分析了存储在个人计算机系统中的脉搏波形数据。对脉冲上升时间进行了研究，发现在20keV~40keV的X射线能量范围内，平行(电矢量/阳极线)情况下的平均上升时间(脉冲峰值的10%~50%)较短。其中一个问题是上升时间绝对值的重复性不好。目前有几种X射线孔隙率测量技术。为了获得更高的偏振灵敏度，散射方法(如布拉格晶体)将是更好的选择。然而，对于X射线天文学的应用而言，采用正比计数器和脉冲波形分析的偏振测量具有以下优点：1)可以测量宽能带的光子；2)同时获得光谱和时间信息。因此，进一步的研究将使这项技术能够实际使用。较少

We have studied digital processing techniques for the pulse shapes of the output signals from X-ray counters. Our first motivation was to reduce particle backgrounds in the proportional counter more efficiently than with usual rise time discrimination method. However, in the course of the study, we noticed that polarimetry of X-ray photons can be done by means of the pulse shape processing (analysis). The basic idea was due to the fact that photoelectrons are preferentially emitted to the direction parallel to the electric vector of the incoming photons. If energy of photoelectron is high enough to reflect its direction of emission to the elongation of the primary electron cloud, pulse shape would be different depending on the geometry between the emission direction and the anode wire. It is expected that for X-ray photons with electric vector parallel to the anode wire the output pulse rises more rapidly than for the vertical case, on average.To examine the idea of "pulse shape (or ri … More se time) X-ray polarimetor", we performed experiments at the synchrotron facility in the Institute for High Energy Physics, Tsukuba, Japan. We irradiated a Xe filled proportional counter against the monochromatic X-ray beam there. Output signals from the preamplifier of the counter were sampled using a Digital Storage Scope. The pulse shape data stored in a personal computer system were analyzed. Rise time of the pulse was investigated, and for X- ray energy from 20 keV to 40 keV, it was found that the average rise time (10%-50% of the pulse peak) was shorter for the parallel (electric vector // anode wire) case. One problem was that reproducibility of the absolute values of the rise time was not good.There are handful of techniques for X-ray poralimetry. To get higher sensitivity for polarization, scattering methods (e. g. Bragg crystal) would be better. However, as for X-ray astronomy use, polarimetry with proportional counter and pulse shape analysis have advantages of 1) photons in wide energy bands can be measured, 2) spectral & timing information is obtained at the same time. Thus further study will enable this technique for actual use. Less