【摘要】：暗物質(zhì)探測已成為21世紀物理學界最重要的課題之一。弱相互作用重粒子(Weakly Interacting Massive Particles,WIMPs)被認為是最有可能的暗物質(zhì)粒子候選者。因它與物質(zhì)作用截面極小,直接探測暗物質(zhì)要求極低的本底環(huán)境。中國暗物質(zhì)實驗(CDEX)計劃利用噸量級低能量閾高純鍺(HPGe)探測器開展低能量暗物質(zhì)直接探測工作。為了進一步降低實驗本底,CDEX第一階段CDEX-1實驗的質(zhì)量為1kg的高純鍺探測器使用碘化鈉反符合探測器。隨著HPGe探測器質(zhì)量增大,固態(tài)的NaI反符合探測器已無法滿足實驗要求。作為CDEX項目的第二階段,CDEX-10實驗使用10 kg HPGe探測器作為主探測器,并計劃利用液氬(LAr)作為HPGe探測器的反符合探測器。這是世界上首個以LAr探測器作為反符合探測器的暗物質(zhì)直接探測實驗。本課題作為CDEX-10 LAr反符合探測器的預研課題,主要研究工作有:(1)設計、研制了一套小型LAr探測器實驗平臺。掌握了LAr探測器的實驗原理和實驗流程,建立了一套LAr探測器數(shù)據(jù)處理方法。這些方法與經(jīng)驗將為CDEX-10 LAr反符合探測器的運行提供借鑒。(2)小型LAr探測器光電子產(chǎn)額的實驗測量與蒙卡模擬研究。研究了PMT的關(guān)鍵性能,測量得到了PMT的絕對增益、分辨率和峰谷比等關(guān)鍵參數(shù)。測量了小型LAr探測器對不同入射位置662 keVγ射線的能譜,得到了對應的光電子產(chǎn)額為0.051~0.079 p.e./keV,并結(jié)合蒙卡模擬確定了小型LAr探測器的閃爍光產(chǎn)額LY、LAr對閃爍光的吸收長度L和Teflon表面的反射率R等關(guān)鍵參數(shù)。這些參數(shù)被應用于CDEX-10 LAr反符合探測器的模擬計算,評估反符合探測器的預期性能。(3)氬閃爍光信號波形的研究。研究了未經(jīng)純化的氬的波形甄別特性,觀察到了γ粒子事件和α粒子事件的快成分比重參數(shù)Fprompt有顯著的差異,為進一步研究LAr反符合探測器的粒子甄別效率提供了可能性。還研究了閃爍光慢成分時間常數(shù)與氬純度的關(guān)系,可作為實時監(jiān)測氬純度的手段。(4)通過蒙卡模擬評估CDEX-10 LAr反符合探測器的預期性能,并對CDEX-10探測器系統(tǒng)的設計和結(jié)構(gòu)提出優(yōu)化建議。模擬得到了當前實驗條件下,CDEX-10 LAr反符合探測器的能量閾值和反符合效率,預測了經(jīng)過反符合后可將CDEX-10的本底降至0.1 cpkkd的物理目標以下。
[Abstract]:Dark matter detection has become one of the most important topics in physics in the 21st century. The weakly interacting heavy particle (Weakly Interacting Massive Particles,WIMPs) is considered the most likely candidate for dark matter particles. Because of its minimal cross section with matter, direct detection of dark matter requires very low background environment. China dark matter experiment (CDEX) plans to use low energy threshold high purity germanium (HPGe) detector to carry out direct detection of low energy dark matter. In order to further reduce the experimental background, the high purity germanium detector with the quality of 1kg in the first stage of CDEX CDEX-1 experiment uses sodium iodide anti-coincidence detector. With the quality of HPGe detector increasing, the solid state NaI counter-coincidence detector can not meet the experimental requirements. As the second phase of the CDEX project, the 10 kg HPGe detector is used as the main detector in the CDEX-10 experiment, and the liquid argon (LAr) is planned to be used as the anti-coincidence detector for the HPGe detector. This is the world's first direct detection of dark matter using a LAr detector as an anti-coincidence detector. As a pre-research task of CDEX-10 LAr anti-coincidence detector, the main research work is as follows: (1) A set of experimental platform of small LAr detector is designed and developed. The experiment principle and flow chart of LAr detector are mastered, and a set of data processing method of LAr detector is established. These methods and experiences will provide a reference for the operation of CDEX-10 LAr anti-coincidence detectors. (2) Experimental measurement and Monka simulation of photoelectron yield of small LAr detectors. The key performance of PMT is studied and the key parameters of PMT, such as absolute gain, resolution and peak-to-valley ratio, are obtained. The energy spectra of small LAr detectors for 662 keV 緯 -rays at different incident positions were measured. The corresponding photoelectron yield was 0.051 ~ 0.079 p.e.keV, and the scintillation light yield LY, of the small LAr detector was determined by combining with Monka simulation. The key parameters such as the absorption length L of LAr and the reflectivity R of Teflon surface are obtained. These parameters are applied to the simulation calculation of CDEX-10 LAr anti-coincidence detector to evaluate the expected performance of the anti-coincidence detector. (3) the study of argon scintillation signal waveform. The waveform discrimination characteristics of unpurified argon have been studied. It has been observed that there are significant differences in the fast component specific gravity parameters Fprompt between 緯 particle events and 偽 particle events, which provides a possibility for further study on the particle discrimination efficiency of LAr anticoincidence detectors. The relationship between the time constant of slow component of scintillation and the purity of argon is also studied, which can be used as a means to monitor the purity of argon in real time. (4) the expected performance of CDEX-10 LAr anti-coincidence detector is evaluated by Monka simulation. The design and structure of CDEX-10 detector system are optimized. The energy threshold and anti-coincidence efficiency of the CDEX-10 LAr anti-coincidence detector are obtained under the current experimental conditions, and it is predicted that the background of CDEX-10 can be reduced to below the physical target of 0.1 cpkkd after the anti-coincidence.
【學位授予單位】：清華大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：P145.9

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