双探头高纯锗γ谱仪灵敏度研究

Sensitivity analysis of gamma spectroscopy system with dual high-purity germanium detectors

在暗物质和中微子等稀有衰变实验中,探测器材料中的放射性核素衰变所产生的射线诱发实验本底,其沉积能量可能与信号能区重叠。精确测量探测器材料的放射性,更好地理解本底来源和控制实验本底是提升探测器灵敏度的关键。高纯锗γ谱仪能量分辨率高,对样品几何形状没有要求,不需要对样品进行破坏性加工,是广泛应用的放射性测量仪器之一。PandaX合作组在锦屏地下实验室已搭建两套高纯锗γ谱仪(JP1和JP2),为暗物质和中微子实验甄选低本底材料。为提升高纯锗γ谱仪的灵敏度,精确测量更低放射性的材料,我们在现有JP1的基础上,设计双探头高纯锗γ谱仪。通过提升效率和降低本底两种方法,对暗物质和中微子实验关心的不同核素,相比于现有JP1,双探头高纯锗γ谱仪灵敏度预期可提升2~4倍。双探头高纯锗γ谱仪还可以用γ-γ符合方法测量小尺寸的样品,这种测量方式的灵敏度随测量时间有显著提升。

[Background]In rare decay experiments,for instance dark matter and neutrino experiments,rays produced by the radioavtive decay in detector material induce extra experiment background,the energy deposition would contaminate the concerned region.Accurately measuring radioactivity of detector materials,better understanding background source,and controlling experimental background are extremely important to improve sensitivity for those detections.With high energy resolution,flexibility for sample geometry and non-destructive processing for samples,high-purity germanium(HPGe)γspectroscopy is a widely used ultra-low radioactive technology.The PandaX collaboration set up two high-purity germaniumγspectroscopies,so-call JP1 and JP2,in Jinping underground laboratory.[Purpose]This study aims to improve the sensitivity ofγspectroscopies,precisely measure materials with lower radioactivity and screen lower radioactive material for dark matter and neutrino experiments by designing a gamma spectroscopy system with dual high-purity germanium detectors based on the existing JP1.[Methods]Two approaches,i.e.,enhancing efficiency and suppressing background were adopted to improve the sensitivity of both HPGe detectors,and the Monto Carlo method was employed to analyze the efficiency and background source of JP1,hence the improved result of dual high-purity germanium detectors was estimated.[Results]For different nuclides concerned in dark matter and neutrino experiments,the minimum detectable activity of dual high-purity germaniumγspectroscopy system is expected to improve by factor of 2~4.This new system can also measure the radioactivity withγ-γcoincidence method to improve the sensitivity for small size samples.[Conclusions]Dual high-purity germaniumγspectroscopy can improve sensitivity of factor 2~4 and apply to developing a newγ-γcoincidence method.