Design and development of fluorescence gas detector for X-ray absorption fine structure

BackgroundThe gas ionization chamber is a kind of intensity monitoring detector widely used in Synchrotron Radiation Facility. Lytle detector is often used to measure the fluorescence signal from the element of interest in the fluorescent mode XAFS (X-ray absorption fine structure), it is one of the important fluorescence detectors for the X-ray absorption spectrum study and used in XAFS beamline station of Shanghai Synchrotron Radiation Facility (SSRF). However, this type detector is predominantly manufactured by foreign company (The EXAFS Company).PurposeThis study aims to develop a domestic fluorescent gas detector according to the operating conditions and technical requirements of fluorescent mode XAFS.MethodsFirstly, a filter and a slit assembly were designed and optimized with Geant4 toolkit. Subsequently, a multilayer grid ionization chamber for fluorescence detection was designed, and the supporting electronics circuit with both high voltage and amplification gain functions was designed. Secondly, all components were manufactured and assembled into a complete detector, and the digital noise, response time, response intensity, and linearity of self-developed detector were tested at BL11B beamline of SSRF. Finally, the actual measured performance of self-developed detector was tested and compared with Lytle detector at BL11B beamline.ResultsThe test results indicate that the digital noise level is approximately ~3.2×10-9 V, which is superior to the (9~10)×10-9 V observed in the Lytle detector. Additionally, the response time is less than 2.1 ms, significantly outperforming the Lytle detector's response time of approximately 150 ms. The linearity of the detector's response also exceeds 0.999 6.ConclusionsThe self-developed detector with shorter response times and better performance than Lytle detector has been achieved, and the localization replacement of the Lytle type detector is realized. Meanwhile, it has been used in the fluorescent mode XAFS of BL11B beamline at SSRF.