Study On The Determination Method Of Very Low Concentration Radon

Neutrino detection and dark matter detection are one of the frontiers of contemporary particle physics research.Cosmological observations indirectly and conclusively prove the existence of dark matter.As the most widely accepted dark matter candidate at present,"weak interaction heavy particles?WIMP?"interacts with ordinary matter with a very small cross-section,and the case rate is less than 1 event/kg/year.Therefore,the neutrino detection and dark matter detection experiments The background has extremely high requirements,and radon pollution is an important source of background.In the dark matter detection experiment,xenon is an excellent medium for direct detection of dark matter.In liquid xenon,the energy of nuclear recoil can be released in the form of photons and ionized electrons,etc.,so that it can be detected.Xenon is used as the detection medium.Commonly used ²¹²Pb beta rays are often used as a low-energy electron recoil energy scale.²¹²Pb is derived from ²²⁰Rn loaded into the xenon detection medium,and its interference nuclide is ²²²Rn daughter²¹⁰Pb.Therefore,for ²²⁰Rn source,the concentration requirements of²²²Rn are very demanding,and a method for measuring the concentration of ²²²Rn in the ²²⁰Rn source is required.At the same time,in the detection of dark matter,there is a detection requirement of 10?Bq/m³ for radon concentration measurement equipment.Therefore,it is planned to use an activated carbon removal radon enrichment device made of very low background activated carbon for radon removal and enrichment,thereby improving the sensitivity of the detector.Therefore,a low background activated carbon is required and its background needs to be measured.Based on the above problems,this paper separately measured the extremely low concentration of ²²²Rn in the ²²⁰Rn source intended for the PandaX detector and the S-H activated carbon intended for the radon enrichment device.For the ²²⁰Rn source intended for the PandaX detector,the RAD7 was used to determine the extremely low ²²²Rn content in the high activity ²²⁰Rn source.The experiment found that in addition to the tailing phenomenon of ²¹⁶Po?particles,the difference in the collection efficiency of ²¹⁸Po and ²¹²Po?particles also one reason caused the measurement of ²²²Rn for the high concentration,and the upper limit of the activity ratio of ²²²Rn/²²⁰Rn in the ²²⁰Rn source is 6.2×10^-5,which is measured by the delay pipeline+RAD7 joint measurement method.For a very low background activated carbon—S-H activated carbon,this article cleans the activated carbon and uses the temperature desorption method to desorb the S-H activated carbon.After packaging,it was sent to the Jinping underground laboratory,and measured its background for three times using the Ge-2 detector.The upper limit of the ²²²Rn precipitation rate of the activated carbon background obtained by fitting was 178.6±20.68 mBq/kg.In addition,the ²²²Rn permeability coefficient of the aluminum core composite membrane bag used in storage was measured to obtain ²²²Rn,and the permeability coefficient is 5.11×10^-1010 cm²/s.