Development Of MBq/m~3 Radon Concentration Measuring Device

Dark matter detection is one of the frontiers of contemporary particle physics research.The cross section of the interaction between dark matter and ordinary matter is very small,and the event rate is<1 event/kg/year.Therefore,there are extremely high requirements for low background in dark matter detection experiments,and ²²²Rn pollution is one of the important sources of background.For dark matter experiments based on liquid xenon,²²²Rn is the most important pollution.²²²Rn will be dissolved in liquid xenon and then distributed almost uniformly in the detector.Therefore,there are strict requirements on the content of ²²²Rn in the detector.The ²²²Rn content of various components needs to be determined before use.In terms of dark matter detection,the concentration of ²²²Rn is required to be lower than the order of m Bq/m³.In order to achieve the above purpose,enrichment radoncold trap device was developed by using activated carbon with a very low ²²⁶Ra background for radon concentration enrichment.The ²²²Rn concentration measuring device performs radon concentration measurement.m Bq/m^{3 222}Rn concentration measurement device,which consists of two parts:enrichment radoncold trap device and a ²²²Rn measurement device.enrichment radoncold trap device consists of two parts:a pressure vessel and a cold trap.According to the working conditions of low temperature enrichment and high temperature desorption,the design of the pressure vessel is completed.The key to the cold trap device lies in the reduction and accurate measurement of the background of the activated carbon with extremely low background.A variety of measures are adopted for the very low background activated carbon to reduce the interference factors of the activated carbon background.The background was measured using Ge-2detectors in the Jinping Underground Laboratory.The activated carbon background is 17.49±9.29 m Bq/kg.The 222Rn measuring device uses electrostatic collection method for measurement.This article investigates the measurement device and completes the design and construction of the measurement device;scales the measurement chambers of different materials and shapes,calculates the scale factor and collection efficiency,and completes the design of the measurement chamber and the construction of the measurement device after comprehensive comparison.Set up the measuring device and measure the background of the existing measuring chamber,the background is 8.93 m Bq/m³.The design and construction of the m Bq/m^{3 222}Rn concentration measurement device provides experience and assistance for the radon laboratory of University of South China to establish a highly sensitive radon laboratory.