The Measurement And Simulation Of Low Background Radioactivity Detector

The detector of JUNO?Jiangmen Underground Neutrino Observatory?uses 20000tons of high purity liquid scintillator to detect the Neutrino signals of nuclear reactor.The basic requirement of the ²³⁸U and ²³²Th radioactivity of liquid scintillator is less than 10^-15 g/g.And the natural radioactivity of liquid scintillator is from 10^-12g/g to10-13 g/g,so it is necessary to purify the natural liquid scintillator.The measurement of the liquid scintillator radioactivity is an important means of quality control in the process of production and purification of liquid scintillation.So it is necessary to build a radioactive measurement to monitor the liquid scintillator activity.There is a small low background radioactivity measurement device in the laboratory building with two PMTs?XP2020?,whose liquid scintillator sample is about80 g.The purpose of building it is groping measurement method to make preparation for the large detector with higher sensitivity.This equipment get the radioactivity of liquid scintillator by measuring the special cascade decay of ²³²Th and ²³⁸U series.²¹²Bi-²¹²Po cascade decay of ²³²Th series and ²¹⁴Bi-²¹⁴Po cascade decay of ²³⁸U series are very unique beta-alpha cascade decay.The half-life of ²¹²Po is 298ns,and the energy of alpha ²¹²Po produces is 1.2MeV after quenching.The half-life of ²¹⁴Po is 163?s,and the energy of alpha ²¹⁴Po produces is 1.0MeV after quenching.Assuming that the radioactivity of all the nuclides in ²³²Th series and ²³⁸U series reach equilibrium state,the activity of all nuclides are same.So the radioactivity of special cascade decay is equal to their corresponding series.This article mainly introduced the measurement of the sensitivity and the detection efficiency of the detector in the lab and the simulation of two detector scheme with higher sensitivity by taking example from some low background radioactivity measurement equipment.