Study of the material photon and electron background and the liquid argon detector veto efficiency of the CDEX-10 experiment

The China Dark Matter Experiment （CDEX） is located at the China Jinping Underground Laboratory （CJPL） and aims to directly detect the weakly interacting massive particles （WIMP） flux with high sensitivity in the low mass region. Here we present a study of tile predicted photon and electron backgrounds including the background contribution of the structure materials of the germanium detector, the passive shielding materials, and the intrinsic radioactivity of the liquid argon that serves as an anti-Compton active shielding detector. A detailed geometry is modeled and the background contribution has been simulated based on the measured radioactivities of all possible components within tile GEANT4 program. Then the photon and electron background level in the energy region of interest （〈10-2events-kg1·day 1·keV-1 （cpkkd）） is predicted based on Monte Carlo simulations. The simulated result is consistent with the design goal of the CDEX-10 experiment, 0.1cpkkd, which shows that the active and passive shield design of CDEX-10 is effective and feasible.

Building of a ton-scale liquid argon prototype detector

Background Based on the unique PSD characteristic which essentially relies on the detector light yield,liquid argon detector is widely used for dark matter searching experiment.The experimental study of how to get larger light yield for a ton-scale liquid argon detector is worth to be carried out.Purpose A ton-scale liquid argon prototype detector is built to check the detector implementation as well as the light collection efficiency.Methods A ton-scale single-phase liquid argon prototype detector is built in the surface laboratory for scalable detector construction experience.The detector adopts the classical spherical arrangement mode to obtain a large PMT photocathode coverage.Forty-two PMTs are immersed in the liquid argon,and polymer materials are used to construct the PMT supporting structures.Totally about 2.2 tons of liquid argon is used,of which about 160 kg is the active volume.In this paper the details of the experiment as well as the detector performance are introduced.Results Experiment results show that the light yield reaches 6.3 PE/keV,with an effective photon collection efficiency of 74.3%achieved.

液氩探测器的低温PMT性能测试

中国暗物质实验(China dark matter experiment,CDEX)拟使用液氩探测器作为高纯锗探测器的反符合探测器,其使用的光电倍增管(photomultiplier tube,PMT)需能长期稳定地工作在液氩温度(87.3K)下.PMT在使用前,须掌握其在低温下的性能情况.文章分别在室温和低温环境中测试了ETL 9357FLA型光电倍增管,获得了单光电子响应、暗计数率以及低温环境中运行的稳定性等重要实验结果.通过详细地对比和分析室温和低温环境中PMT的性能表现,确认该型PMT能在低温环境中正常运行.

暗物质地下探测的前沿技术预研2013年年度报告

“暗物质地下探测的前沿技术预研”主要研究内容是综合前一阶段惰性液体探测器方案、晶体探测器方案、过热液滴探测器方案均基本按计划进行：惰性液体探测器方面,实现液氩模型探测器系统的搭建,实现低温系统、氩气液化、模型探测器系统密封与检测、TPB波长位移板镀膜、高纯氩气纯化、单相液氩发光并探测,为下一步研究、发展液氩探测技术,研究相关探测器参数,实现液氩探测器在锦屏进行地下暗物质的探测打下了基础;并将进一步研究单相液氩探测器的相关参数,研究两相探测方案;晶体探测器已利用北京大学中子束流的进行了n/gamma的相关测试,测试结果表明探测系统、方法工作正常,本底可控,并可以进一步预期使用原子能院更高（3~4个量级）强度束流测试将可达到比较好的测试结果,并实现对晶体n/gamma鉴别能力的定量测量,以确定晶体探测器方案的本底;同时我们将进行18 kg晶体模型探测器的最后组装及测试工作,研究探测器耦合介质、探测器响应、本底水平等;晶体探测技术成熟,大质量的晶体探测器在暗物质探测的截面测量方面仍有一定的优势,特别是在质子自旋相关的暗物质探测方面有显著的优势;过热液滴的气泡探测技术仍然在不断地进步中,截止目前,该课题组已发展并使用放射源测量了过热液滴探测器,实现了探测器对中子的灵敏响应、对gamma的惰性响应;研究了气泡探测器声音信号的频谱特征,设计并初步开发了信号的声频识别系统。我们将继续跟踪国际最新动向,发展相关探测、识别技术。

液氩模型探测器预研进展研究

液氩探测器是一种被广泛使用的粒子物理探测技术,在加速器实验中早就被用于粒子探测,如,Atlas实验、D0实验的量能器,在未来实验中可以应用在探测太阳中微子、超新星中微子、长基线中微子、暗物质、质子衰变等新物理中,如,LBNE等中微子实验、Ar DM、DEAP/CLEAN及Darkside等几代暗物质探测实验。液氩发光机制本身具备约亿倍的中子-伽玛分辨能力,远远超过了其他闪烁材料,对寻找稀有事例的暗物质探测非常重要,目前液氩这项多用途的探测器技术在国内还没有发展起来。研究的一个重要方面是致力于基于国内工业水平来研制液氩探测器,以期掌握探测器核心技术和降低研制成本。我们将基于液氮制冷的原理研制高温度稳定水平的探测器低温系统,基于国产锆基吸气剂研制高洁净度的氩气净化系统,用低温光电倍增管作为信号读出设备,测量液氩探测器的闪烁光,进行物理研究。该文报告液氩模型探测器预研的相关进展。

暗物质探测实验液氩反符合探测器杂质影响分析

CDEX装置采用液氩反符合屏蔽方法降低本底,液氩中的杂质可能会对反符合效率造成影响。CDEX装置反符合效率与高纯锗晶体总探测效率、液氩探测器总探测效率有关。6个因素会影响液氩探测器总探测效率。液氩中的杂质会改变慢成分衰减时间。杂质通过焠灭和吸收作用,降低闪烁光产额和吸收闪烁光子,进而降低反符合探测效率。以氮和氧为例,计算了不同含量时发生的焠灭作用对于反符合效率的影响。结果表明,仅考虑焠灭作用条件下,为了使反符合效率达到90%以上,需要将液氩介质中的氮和氧含量降低到约100 ppb量级。