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

技术摘要：基于气相电子倍增器（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（ppm）及以下稀元素不可缺少的工具。当样品中稀释元素的原子被调谐能量同步辐射光束激发时，它们会发出微弱的X射线荧光信号。荧光x射线信号穿透力低，被空气严重衰减，在电离室中电离的电子很少。传统的荧光探测器由于信噪比低，检测初级电子电荷信号非常困难。为了提高信噪比，我们建议在电离室中使用单个和多个气体电子倍增器（GEM）来无噪音地放大电离的初级电子电荷。放大后的电荷将提高信噪比，改善检测、分析，便于对稀样品进行表征。传统荧光探测器受微声振动、温度、光的影响，信噪比小，增益随时间偶有漂移。基于GEM的探测器是刚性的，防气体泄漏，允许级联多个GEM进行增益控制，避免由于单个GEM引起的高场火花放电，具有无噪声电子放大，并允许以高速率测量快速信号。该探测器具有灵活的x射线入口窗口尺寸，灵活的接受立体角，可变的GEM尺寸，使用多种气体混合物，在大气压和室温下工作。该项目是与摩根州立大学、布鲁克海文国家实验室（BNL）和巴吞鲁日南方大学合作进行的，旨在加强、教育和培训少数民族学生建造新的探测器，这些探测器将用于国家同步加速器光源（NSLS）和其他国家和国际实验室。非技术摘要：在天然或人造样品中检测百万分之十及以下的稀释元素需要高信噪比（S/N）检测器。当被测试的稀释元素被调谐能量同步加速器光束线激发时，它释放出一种特征荧光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大噪声干扰，这种初级电荷信号太小而无法检测。提出的探测器使用气体电子倍增器（GEM），将稀释元素荧光x射线产生的小初级电荷倍增或放大。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，提供高信噪比。这样可以更好地检测和表征各种样品中的稀元素。该项目是与摩根州立大学、布鲁克海文国家实验室（BNL）和巴吞鲁日南方大学合作进行的，旨在加强、教育和培训少数民族学生建造新的探测器，这些探测器可以用于国家同步加速器光源（NSLS）和其他国家和国际实验室。

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.