MRI:Development of Gas Electron Multiplier Based Fluorescence X ray Detector for Dilute Elements

技术摘要：基于气体电子倍增器(GEM)的荧光X射线气体探测器是利用X射线荧光光谱(XFS)表征百万分之十及以下稀薄元素的必不可少的工具。当样品中的稀元素原子被调谐的能量同步辐射光束线激发时，它们发出微弱的X射线荧光信号。荧光X射线信号穿透能力低，受到空气的严重衰减，在电离室中电离很少的电子。用传统的低信噪比(S/N)的荧光探测器很难探测到微小的一次电子电荷信号。为了提高S/N比，我们提出了使用单个和多个气体电子倍增器(GEM)在电离室中无噪声地放大电离的初级电子电荷。放大后的电荷将提高S/氮比，改善检测和分析，有利于稀释样品的表征。传统的荧光探测器受微声振动、温度、光线等因素的影响，S/N比较小，增益随时间偶尔漂移。基于GEM的探测器坚固、防气体泄漏、允许级联多个GEM用于增益控制、避免因单个GEM而产生的高场火花放电、具有无噪声电子放大，并允许测量具有高速率能力的快速信号。该探测器具有灵活的X射线入射窗口大小，灵活的固体接收角度，可变的宝石尺寸，使用多种混合气体，在常压和室温下工作。该项目与摩根州立大学、布鲁克海文国家实验室(BNL)和南方大学巴吞鲁日大学合作实施，以增强、教育和培训少数族裔学生建立新的探测器，这些探测器将用于国家同步辐射光源(NSLS)和其他国家和国际实验室。非技术摘要：检测天然或制造样品中百万分之十及以下的稀释元素需要高信噪比(S/N)探测器。当被测试的稀有元素被调谐的能量同步光束线激发时，它释放出一种特征的荧光X射线，用于电离产生电荷信号的惰性气体。由于电子放大器引入的噪声干扰很大，这种一次电荷信号太小而无法检测到。提出的探测器使用气体电子倍增器(GEM)，它倍增或放大稀元素荧光X射线产生的小一次电荷。GEM放大的电荷信号幅度远远超过电子放大器产生的噪声水平，提供了高的S/N比。这将允许更好地检测和表征各种样品中的稀释元素。该项目是与摩根州立大学、布鲁克海文国家实验室(BNL)和南方大学巴吞鲁日大学合作实施的，旨在加强、教育和培训少数族裔学生建造可用于国家同步加速器光源(NSLS)和其他国家和国际实验室的新探测器。

Technical abstract:Gas Electron Multiplier (GEM) based fluorescence X-ray gas detector is an indispensable tool for characterizing dilute elements of 10 parts per million (ppm) and below using X-ray Fluorescence Spectroscopy (XFS). When atoms of a dilute element in a sample are excited by a tuned energy synchrotron radiation beamline, they emit weak X ray fluorescence signal. The fluorescence X-ray signal has low penetrating power, is severely attenuated by air, and ionizes few electrons in an ionization chamber. Detecting the small primary electronic charge signal is very difficult using conventional fluorescence detectors with low signal to noise (S/N) ratio. To improve the S/N ratio, we propose to use a single and multiple gas electron multiplier (GEM) to amplify the ionized primary electronic charge without noise in an ionization chamber. The amplified charge will enhance the S/N ratio, improve the detection, analysis, and facilitate to characterize dilute samples. Conventional fluorescence detectors are affected by micro phonic vibrations, temperature, light, have small S/N ratio, and occasional gain drift with time. The GEM based detector is rigid, gas leak proof, allows cascaded multiple GEMs for gain control, avoids spark discharge from high fields due to a single GEM, has noise free electron amplification, and allows measuring fast signal with high rate capability. The detector has flexible window size for x-ray entrance, flexible solid angle of acceptance, variable GEM dimension, uses multiple gas mixtures, operates at atmospheric pressure, and at room temperature. This project is performed in collaboration with Morgan State University, Brookhaven National Laboratory (BNL), and Southern University Baton Rouge to enhance, educate and train minority students in building new detectors that will be used at the National Synchrotron Light Source (NSLS) and at other national and international laboratories.Non-technical abstract:Detecting dilute elements of ten parts per million and below, in natural or manufactured samples requires a high signal to noise (S/N) ratio detector. When a dilute element under test is excited by a tuned energy synchrotron beamline, it releases a characteristic fluoresce X-ray that is used to ionize a noble gas producing a charge signal. This primary charge signal is too small to be detected because of the large noise interference introduced by electronic amplifiers. The proposed detector uses a gas electron multiplier (GEM) that multiplies or amplifies the small primary charge created by the dilute element fluorescence X-ray. The GEM amplified charge signal amplitude far exceeds the level of the noise produced by the electronic amplifiers providing a high S/N ratio. This will allow better detection and characterization of dilute elements in various samples. This project is performed in collaboration with Morgan State University, Brookhaven National Laboratory (BNL), and Southern University Baton Rouge to enhance, educate, and train minority students in building new detectors that can be used at the National Synchrotron Light Source (NSLS) and at other national and international laboratories.