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

本文研究了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减少粒子背景的比例计数器更有效地比通常的上升时间的歧视方法。然而，在研究过程中，我们注意到，X射线光子的偏振测量可以通过脉冲形状处理（分析）来完成。其基本思想是由于光电子优先发射到平行于入射光子的电矢量的方向。如果光电子的能量足够高以将其发射方向反映到初级电子云的伸长，则脉冲形状将取决于发射方向和阳极丝之间的几何形状而不同。预期对于具有平行于阳极线的电矢量的X射线光子，输出脉冲平均比垂直情况下上升得更快。 ...更多信息 我们在日本筑波高能物理研究所的同步加速器装置上进行了实验。我们用单色的X射线束照射一个装满铯的正比计数管。使用数字存储示波器对来自计数器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冲波形数据。研究了脉冲的上升时间，并且对于从20 keV到40 keV的X射线能量，发现对于平行（电矢量//阳极线）情况，平均上升时间（脉冲峰值的10%-50%）较短。一个问题是上升时间的绝对值的可重复性不好。X射线孔隙度测定法有几种技术。为了获得更高的偏振灵敏度，散射方法（如。G.布拉格晶体）会更好。然而，对于X射线天文学用途，具有比例计数器和脉冲形状分析的偏振测量具有以下优点：1）可以测量宽能带中的光子，2）同时获得光谱和定时信息。因此，进一步的研究将使这项技术的实际应用。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