摘要
本文研究了基于上海激光电子γ源(Shanghai Laser Electron Gamma Source,SLEGS)的两种正电子束产生方法,通过蒙特卡罗程序Geant4模拟研究了单靶磁场分离和多靶侧向引出模式下的正电子靶选择、偏转磁铁和聚焦系统设置、本底干扰及抑制等,根据模拟分析,优化了正电子束流产生参数,在SLEGS获得MeV能级的高质量正电子束流并建设正电子束应用平台,将SLEGS的研究扩展到正电子束湮灭实验等应用领域。在SLEGSγ射线能量在0.66~21.7 MeV连续可调,γ束流强度约10^(7)photons·s^(−1)条件下,通过单靶磁场分离模式得到了正电子能量范围为1.0~12.9 MeV,流强密度为10^(2)~10^(3)e^(+)·s^(−1)·cm^(−2)的正电子束。优化的螺线管多靶侧向引出模式使正电子束具有更好的流强和能量分辨,并可有效避免了γ本底的影响,最后得到的正电子能量范围为1.0~9.1 MeV,流强密度为10^(3)~10^(5)e^(+)·s^(−1)·cm^(−2)。实验测量了SLEGS正电子湮灭产额及γ射线角分布,LaBr3(Ce)探测器测量得到全空间正电子湮灭γ射线约为2.5×10^(8)photons,而模拟计算中4π立体角收集得到的511 keV射线总计数为2.47×10^(8)photons,在误差范围内与模拟结果符合一致,验证了模拟分析的可靠性。SLEGS正电子湮灭寿命动量谱测试实验表明:现有条件下正电子起始时间难以准确测量,未来考虑从储存环加速器高频或者短脉冲激光触发等方法引出更准确的起始时间信号,从而获得合理正电子湮灭寿命谱。
[Background]Positron beams have extensive applications in positron emission tomography(PET)and non-destructive testing(NDT),with positron annihilation techniques providing valuable insights into submicroscopic defects.Among various generation methods,pair production through gamma-matter interaction is one of the most effective approaches.[Purpose]This study aims to develop a high-quality positron beam with adjustable energy at MeV levels using the continuously adjustable gamma beam at the Shanghai Laser Electron Gamma Source(SLEGS)of the Shanghai Synchrotron Radiation Facility(SSRF).[Methods]Firstly,two positron beam generation and separation methods at SLEGS were investigated using continuously adjustable gamma rays(0.66~21.7 MeV)with intensity of~10^(7)photons·s^(−1)to interact with selected target materials.Secondly,comprehensive Monte Carlo simulations were conducted using Geant4 software to optimize target materials,target thickness,deflecting magnet configurations,and focusing systems for both single-target magnetic field separation and multi-target lateral extraction modes.Finally,experimental verification was performed by directly injecting gamma beams into lead targets,measuring the angular distribution of 511 keV annihilation gamma rays using LaBr3(Ce)detectors,and conducting preliminary positron annihilation lifetime spectroscopy measurements.[Results]Verification results show that the single-target magnetic field separation mode achieves positron beams with energy ranging from 1.0 MeV to 12.9 MeV and intensity of 10^(2)~10^(3)e^(+)·s^(−1)·cm^(−2).The optimized multi-target lateral extraction mode significantly improves beam quality,yielding positrons with energy range of 1.0~9.1 MeV and intensity of approximately 10^(3)e^(+)·s^(−1)·cm^(−2)in the low-energy region and 10^(5)e^(+)·s^(−1)·cm^(−2)in the high-energy region.The scattered gamma background is successfully reduced by approximately one order of magnitude in this configuration.Experimental measurements yield 2.5×10^(8)annihilation photons in full space,showing excellent agreement with the simulation result of 2.47×10^(8)photons within error margins.[Conclusions]Monte Carlo simulations successfully optimize SLEGS positron beam parameters,with experimental verification confirming the simulation's reliability.The optimized solenoid multi-target lateral extraction mode enhances positron beam intensity while effectively eliminating scattered gamma background interference.Under current experimental conditions,accurate measurement of positron start time remains challenging for positron annihilation lifetime spectroscopy.Future improvements will focus on obtaining more precise start time signals from the SSRF storage ring high-frequency system or implementing short-pulse laser triggering methods to achieve reasonable positron annihilation lifetime spectra.
作者
金晟
郝子锐
许杭华
周位鑫
陈开杰
杨宇萱
刘龙祥
张岳
孙乾坤
王振伟
徐孟珂
王向飞
范功涛
王宏伟
JIN Sheng;HAO Zirui;XU Hanghua;ZHOU Weixin;CHEN Kaijie;YANG Yuxuan;LIU Longxiang;ZHANG Yue;SUN Qiankun;WANG Zhenwei;XU Mengke;WANG Xiangfei;FAN Gongtao;WANG Hongwei(Shanghai Institute of Applied Physics,Chinese Academy of Sciences,Shanghai 201800,China;University of Chinese Academy of Sciences,Beijing 100080,China;Shanghai Advanced Research Institute,Chinese Academy of Sciences,Shanghai 201210,China;Department of Engineering Physics,Tsinghua University,Beijing 100084,China;School of Physical Science and Technology,ShanghaiTech University,Shanghai 201210,China;School of Physics,Zhengzhou University,Zhengzhou 450001,China)
出处
《核技术》
北大核心
2026年第1期78-87,共10页
Nuclear Techniques
基金
国家重点研发计划(No.2022YFA1602404,No.2023YFA1606901)
国家自然科学基金(No.12275338,No.12388102,No.U2441221)资助。
