Design And Performance Study Of A CsI(Tl)position Sensitive Scintillation Detector

Position-sensitive detectors can provide location information of particles,which play an important role in nuclear physics experiments,radioactive beam monitoring,radioactive source monitoring and searching.CsI（Tl）scintillator position sensitive detector is composed of CsI（Tl）array,light guide and photomultiplier tube array.When detecting gamma rays,different light distribution is generated on the photomultiplier tube array to achieve position resolution.Light guide has a significant effect on light distribution and is one of the key components of scintillator position sensitive detectors.Therefore,based on Monte Carlo simulation method and experimental means,a scheme is proposed to improve the position resolution performance of CsI（Tl）scintillation position-sensitive detector by optimizing the light guide design of the detector.In the aspect of simulation,Geant4 software was used to model the material,geometry and physical processes involved in CsI（Tl）scintillator position sensitive detector.Different light guide,grooving mode and grooving depth were selected to analyze and summarize the influence rule of the above factors on the reconstruction error and position resolution performance according to the position reconstruction effect of each one,and the light guide scheme in line with the design objective was given.It was found that the increase of photoconductivity thickness would reduce the photon transmittance and widen the position resolution,but could improve the uniformity and monotony of position reconstruction of edge pixels of scintillator.Different groove depths can adjust the offset direction of the reconstructed position.Therefore,choosing different groove depths in different regions can correct the monotonicity of the reconstructed position and improve the compression effect.For the design target of the detector,the light guide with thickness of 14mm was selected.The pixel unit corresponding to the scintillator was cut with three grooves of different depths inside,in the middle and outside of the light guide.A scheme suitable for pixel CsI（Tl）scintillator and multianode photomultiplier array was presented.It had been verified that the average error of the corrected position reconstruction was 1.0mm,which improved the performance by more than 4 times compared with the scheme without grooving,and effectively improves the compression effect brought by the center of gravity method.In the aspect of experiment,a test platform for CsI（Tl）scintillation position sensitive detector was designed based on NIM crate and its electronics plug-in.Meanwhile,referring to the testing needs of similar detectors and components,the functions of component testing and batch testing were expanded,which had stronger universality.The platform can not only test and calibrate the performance of scintillators and photoelectric conversion devices alone,but also test the complete detector prototype by combining grating,collimating hole,coding plate and other collimating devices.Before the formal experiment,the photomultiplier tube test and gain leveling experiment were carried out using the platform,which effectively improved the response inconsistency of the detector.Based on the above platform,a prototype of CsI（Tl）scintillation position sensitive detector was designed and tested with a collimated ²²Na point source.The effects of different light guide thickness,different signal processing methods and different incident regions on the position resolution of the detector were studied.The size of pixel CsI（Tl）scintillator used in the experiment is 70 mm×70 mm×10 mm,and the number of crystal arrays is 63×63.The pixel fluorescence distribution of the scintillator after cutting is narrow,which can effectively improve the compression effect when the particles are incident from the edge.The classical center of gravity method is used in position reconstruction algorithm,which is simple in principle and convenient in calculation.The position reconstruction results of the detector prototype before and after adding the photoguide were compared.Finally,position resolution better than 5.6 mm was obtained in 5 mm slit test.The experimental results were compared with the simulation results,which verified the feasibility of the position resolution performance optimization scheme of the detector.