Key Technology Research Of Liquid Argon Veto Detector In CDEX

Dark matter is one of the most important subjects of physics in the 21 st century.Weakly Interacting Massive Particles(WIMPs)are the most popular candidates of dark matter in our universe.A low background level is required in the direct detection of dark matter due to the little interaction cross section between dark matter and materials.The China Dark Matter Experiment(CDEX)Collaboration has been aiming to search for low mass WIMPs with a ton-scale highly pure germanium(HPGe)detector.In order to suppress the background,an anti-coincidence veto detector is employed in CDEX,acting as the active shielding.However,active shielding system with solid scintillators has to be abandoned as the Ge detector get larger in the following phases of CDEX experiments.The Liquid Argon(LAr)veto is proposed in the second phase CDEX-10 which is the first dark matter direct detection experiment using LAr detector as an anti-coincidence veto detector.This dissertation work is focused on the R&D of CDEX-10 LAr veto detector,which contains:(1)Designing and building a prototype of the liquid argon detector.The principle of the LAr detector experiment and the operating processes have been mastered.The methods of data analysis have been developed.All of these will help to the operation of the CDEX-10 LAr veto detector.(2)Measurement and the Monte Carlo simulation of the photoelectron yield of the prototype LAr detector.The key performances of the PMTs,including the absolute gain and the resolution and the peak to valley ratio,have been measured.The photoelectron yields of the prototype LAr detector have been measured to be 0.051-0.079 p.e./keV for 662 keV ? lines at different positions.With the Monte Carlo simulation,the important parameters such as the light yield of the LAr detector,the absorption length for scintillation photons in liquid argon and the reflectivity of Teflon have been determined.These important parameters were used in the simulation of the CDEX-10 LAr veto detector and the performance of which were estimated.(3)Research of pulse shape of the LAr scintillation lights.The pulse shape discrimination of ? particles and ? particles has been studied.The prompt fraction Fprompt was found to be different between the ? particles and ? particles,which provides the possibility to develop the pulse shape discrimination method of the LAr detector which is unpurified.In addition,the relationship between the slow component lifetime of Ar scintillation lights and the Ar purity has also been studied.The purity of LAr can be monitored through this method.(4)The performance of the CDEX-10 LAr veto detector has been estimated by Monte Carlo simulation.And the design of CDEX-10 experiment was optimized.The energy threshold and the veto efficiency of the LAr veto detector was got through simulation.The background of CDEX-10 was simulated to be < 0.1 cpkkd after the active shielding of the LAr veto detector.