掺钆液闪中子探测器的研制

中子在探测器中能产生与暗物质粒子（WIMPs）类似的核反冲信号,对于低背景的暗物质直接探测实验,精确测量和排除中子的干扰尤其重要。为测量中国锦屏地下实验室(CJPL)中子本底的通量,研制了高效的、具有很强中子-伽马分辨的掺钆液闪快中子探测器。介绍了掺钆液闪中子探测器的研制和性能,包括探测器形状和尺寸的设计,液体闪烁体类型、光电倍增管型号以及液闪容器材料的选择,探测器的伽马能量刻度以及中子与伽马信号的甄别。用Am-Be中子源对探测器进行探测效率刻度,得到阈值为0.2 MeV等效电子能量的中子探测效率为(6.300.30)%,满足中国锦屏地下实验室对中子通量测量的要求。     

利用252 Cf快裂变室测量BC501A液闪探测器的相对探测效率和响应函数

本文利用²⁵²Cf快裂变室和多参数数据采集系统,逐事例的同时记录了自发裂变中子和瞬发伽马的飞行时间(TOF),脉冲形状甄别(PSD)和反冲能量(RE,裂变中子是通过测量反冲质子;瞬发伽马是通过测量康普顿反冲电子)三维信息.详细介绍了通过离线数据分析完全扣除三维信息中的伽马事例贡献,以获得Φ50.8 mm×50.8 mm的BC501A液闪探测器的相对探测效率和响应函数的方法.在不通过探测器响应函数进行数据转换的条件下,利用中子的能量直接确定了中子的有效测量阈值.得到的中子 关键词： 252Cf快裂变室')" href="#">²⁵²Cf快裂变室 BC501A液闪探测器 相对探测效率 响应函数     

暗物质寻找实验中CsI(Tl)晶体反符合探测器实验研究

一个正在建设的位于韩国Y2L地下实验室的低能暗物质探测实验中, 采用了CsI(Tl)晶体反符合探测器作为主动屏蔽体. 本工作对CsI(Tl)晶体反符合探测器的实验性能进行了研究. 通过FADC系统记录的脉冲波形数据, 研究了探测器的能量分辨率和波形甄别的能力; 研究相同能量γ射线入射到反符合探测器不同位置的相对光输出将有助于选择探测器的工作参数; 为了解晶体自身放射性对暗物质测量的影响, 利用低本底HPGe探测器对CsI(Tl)晶体内部的放射性进行了测量, 得到晶体内部Cs同位素的放射性活度. 探测器系统进行了约18d的试运行取数. 实验数据表明, CsI(Tl)晶体探测器的反符合效率约为31% HPGe探测器的本底计数率水平约为133cpd. 为了进行暗物质探测研究, 需要采取有效的方法进一步降低探测器的本底水平.     

PandaX 暗物质探测实验

PandaX是一个位于四川锦屏地下实验室的大型粒子与天体物理稀有事件探测实验装置。PandaX的一期和二期实验利用二相型氙时间投影室技术来直接探测弱相互作用暗物质粒子。PandaX一期实验已经完成,它使用了120 kg氙以检验以往其他实验所发现的疑似信号,其结果在标准假设下否定了这些疑似信号。PandaX二期升级了探测器,使用了500 kg的氙,预期在2015年晚些时候正式开始数据采集以寻找暗物质,将有望拓展暗物质探测的极限。     

CsI(Tl)晶体中反冲Cs和I核Quenching?Factor的测量

许多实验对用CsI(Tl)闪烁晶体作为探测器来寻找和探测暗物质的可行性进行了研究.本工作利用8MeV单能中子轰击CsI(Tl)晶体探测器来研究Cs核和I核的QuenchingFactor.在数据处理中,运用脉冲形状甄别(PSD)方法来分辨反冲核信号和本底信号.实验结果表明,在7keV到132keV的能区中,Quench ingFactor随着反冲核能量的减少而增加.在探测暗物质的实验中,这一性质对于CsI(Tl)晶体探测器获得较低的能量阈值是很有利的.     

极深地下探秘宇宙的“熊猫X”实验

近百年的天文学观测表明宇宙中有大量看不见的“暗物质”存在,但是我们对暗物质的本质却所知甚少。宇宙中也充斥着一种很像暗物质的“幽灵粒子”——中微子,它们的身上也有着众多未解之谜。对暗物质和中微子研究的突破很可能带来下一次物理学的革命。国际上最深的、位于四川凉山州的中国锦屏地下实验室为这样的实验研究提供了得天独厚的场所。过去的20年,液氙探测技术的发展使之成为了探测暗物质、研究中微子性质的核心手段之一。文章主要介绍了暗物质与中微子的未解之谜、液氙探测技术的发展、国内外一些液氙实验的发展态势以及我国液氙探测暗物质“熊猫X”实验的现状和未来。     

暗物质寻找实验中CsI（T1）晶体反符合探测器实验研究

一个正在建设的位于韩国Y2L地下实验室的低能暗物质探测实验中,采用了CsI（T1）晶体反符合探测器作为主动屏蔽体.本工作对CsI（T1）晶体反符合探测器的实验性能进行了研究.通过FADC系统记录的脉冲波形数据,研究了探测器的能量分辨率和波形甄别的能力;研究相同能量γ射线入射到反符合探测器不同位置的相对光输出将有助于选择探测器的工作参数;为了解晶体自身放射性对暗物质测量的影响,利用低本底HPGe探测器对CsI（T1）晶体内部的放射性进行了测量,得到晶体内部Cs同位素的放射性活度.探测器系统进行了约18d的试运行取数.实验数据表明,CsI（T1）晶体探测器的反符合效率约为31%,HPGe探测器的本底计数率水平约为133cpd.为了进行暗物质探测研究,需要采取有效的方法进一步降低探测器的本底水平.     

CsI（TI）晶体中反冲Cs和I核Quenching Factor的测量

许多实验对用CsI(Tl)闪烁晶体作为探测器来寻找和探测暗物质的可行性进行了研究。本工作利用8MeV单能中子轰击CsI(Tl)晶体探测器来研究Cs核和I核的Quenching Factor。在数据处理中，运用脉冲形状甄别（PSD）方法来分辨反冲核信号和本底信号。实验结果表明，在7keV到132keV的能区中，Quenching Factor随着反冲核能量的减少而增加。在探测暗物质的实验中，这一性质对于CsI(Tl)晶体探测器获得较低的能量阈值是很有利的。     

基于前冲康普顿电子高能伽马能谱测量系统设计

除中子外,聚变核心同时释放大量高能伽马,其能谱可反映聚变过程的关键物理参数,并为过程诊断提供重要信息.由于聚变伽马的时间与能量特性,需要设计高探测效率及能量分辨率的伽马谱仪.根据高能伽马谱仪的概念设计(gamma-to-electron magnetic spectrometer),针对该系统中伽马-电子转换靶、电子偏转汇聚、电子探测等关键环节进行优化设计以提高系统探测效率及能量分辨率.其中采用Monte-Carlo程序Geant4模拟研究了伽马-电子转换靶中康普顿散射与多次库仑散射对由转换靶出射电子的能谱与角分布的影响.开发并行遗传算法对复杂几何偏转磁场参数进行优化,得到低强度(小于100 Gauss)复杂边界偏转磁场.根据系统优化设计结果,采用Geant4模拟了该系统对不同能量伽马的响应.此外,还可模拟该系统对特征聚变伽马能谱的测量,结果显示,该系统可在聚变中子产额分别为2.5×10~(15)及1.2×10~(16)条件下,对10—20 MeV高能伽马能谱测量实现能量分辨分别满足0.5 MeV(小于5%)及0.25 MeV(小于2.5%),说明该系统可用于聚变过程伽马能谱的诊断.     

基于大功率LED的中子墙光刻度系统

光刻度系统是中子墙探测器系统的重要组成部分, 用于中子墙前端电子学的刻度和探测器工作性能变化的监测. 通过对基于发光二极管(LED)作为光源的中子墙光刻度系统方案开展了细致的测试研究, 确定了基于快脉冲驱动的大功率蓝光LED(3W)的中子墙光刻度系统方案, 对中子墙探测单元进行了初步刻度测试, 刻度结果能很好地满足光刻度要求, 表明对于快塑料闪烁体探测器该方案是一种较为理想的方案.     

Searching for universal behaviour in superheated droplet detector with effective recoil nuclei

Energy calibration of superheated droplet detector is discussed in terms of the effective recoil nucleus threshold energy and the reduced superheat. This provides a universal energy calibration curve valid for different liquids used in this type of detector. Two widely used liquids, R114 and C₄F₁₀, one for neutron detection and the other for weakly interacting massive particles (WIMPs) dark matter search experiment, have been compared. Liquid having recoil nuclei with larger values of linear energy transfer (LET) provides better neutron-γ discrimination. Gamma (γ) response of C₄F₁₀ has also been studied and the results are discussed. Behaviour of nucleation parameter with the effective recoil nucleus threshold energy and the reduced superheat have been explored.     

Identification of weakly interacting massive particles through a combined measurement of axial and scalar couplings

We study the prospects for detecting weakly interacting massive particles (WIMPs) in a number of phenomenological scenarios, with a detector composed of a target simultaneously sensitive to both spin-dependent and spin-independent couplings, as is the case of COUPP (Chicagoland Observatory for Underground Particle Physics). First, we show that sensitivity to both couplings optimizes chances of initial WIMP detection. Second, we demonstrate that, in case of detection, a comparison of the signal on two complementary targets, such as in COUPP CF3I and C4F10 bubble chambers, allows a significantly more precise determination of the dark matter axial and scalar couplings. This strategy would provide crucial information on the nature of the WIMPs and possibly allow discrimination between neutralino and Kaluza-Klein dark matter.     

Review of dark matter direct detection experiments

Matter, as we know it, makes up less than 5% of the Universe. Various astrophysical observations have confirmed that one quarter of the Universe and most of the matter content in the Universe is made up of dark matter. The nature of dark matter is yet to be discovered and is one of the biggest questions in physics. Particle physics combined with astrophysical measurements of the abundance gives rise to a dark matter candidate called weakly interacting massive particle (WIMP). The low density of WIMPs in the galaxies and the extremely weak nature of the interaction with ordinary matter make detection of the WIMP an extraordinarily challenging task, with abundant fakes from various radioactive and cosmogenic backgrounds with much stronger electromagnetic interaction. The extremely weak nature of the WIMP interaction dictates detectors that have extremely low naturally occurring radioactive background, a large active volume (mass) of sensitive detector material to maximize statistics, a highly efficient detector-based rejection mechanism for the dominant electromagnetic background and sophisticated analysis techniques to reject any residual background. This paper reviews currently available major technologies being pursued by various collaborations, with special emphasis on the cryogenic Ge detector technology used by the Cryogenic Dark Matter Search Collaboration (CDMS).     

Low-energy neutrino and dark matter physics with sub-keV germanium detectors

The TEXONO-CDEX Collaboration (Taiwan experiment on neutrino?CChina dark matter experiment) explores high-purity germanium (HPGe) detection technology to develop a sub-keV threshold detector for pursuing studies on low mass weakly interacting massive particles (WIMPs), properties of neutrino and the possibilities of neutrino-nucleus coherent scattering observation. This article will introduce the facilities of newly established China Jing-Ping Underground Laboratory (CJPL), preliminary result of cosmic ray background studies at CJPL, the dark matter studies pursued at Kuo-Sheng Neutrino Laboratory (KSNL) and research efforts to accomplish our physics goals.     

Dark matter searches by the Boulby Collaboration and liquid xenon prototype development

The current status of direct dark matter searches by the Boulby Dark Matter Collaboration is presented with the latest result from the ZePLiN I liquid xenon detector. An upper limit in the interaction cross section per nucleon of ～1×10^?6 pb for a WIMP mass of 100 GeV is found. Details of ZePLiN’s II and III—two future liquid xenon dark matter are presented. Extensive two-phase liquid-gas xenon prototype work has been undertaken and results of characterization studies are presented. The detector response to internal alpha and external gamma and neutron sources is shown. The potential discrimination power of the two-phase technique is displayed. Finally, prospects for the future dark matter search program are discussed.     

First results from the XENON10 dark matter experiment at the Gran Sasso National Laboratory

The XENON10 experiment at the Gran Sasso National Laboratory uses a 15 kg xenon dual phase time projection chamber to search for dark matter weakly interacting massive particles (WIMPs). The detector measures simultaneously the scintillation and the ionization produced by radiation in pure liquid xenon to discriminate signal from background down to 4.5 keV nuclear-recoil energy. A blind analysis of 58.6 live days of data, acquired between October 6, 2006, and February 14, 2007, and using a fiducial mass of 5.4 kg, excludes previously unexplored parameter space, setting a new 90% C.L. upper limit for the WIMP-nucleon spin-independent cross section of 8.8x10(-44) cm2 for a WIMP mass of 100 GeV/c2, and 4.5x10(-44) cm2 for a WIMP mass of 30 GeV/c2. This result further constrains predictions of supersymmetric models.     

Nonthermal production of weakly interacting massive particles and the subgalactic structure of the universe

There is increasing evidence that conventional cold dark matter (CDM) models lead to conflicts between observations and numerical simulations of dark matter halos on subgalactic scales, which rules out the favored candidates for CDM, namely weakly interacting massive particles (WIMPs). We propose a mechanism of nonthermal production of WIMPs and study its implications on the power spectrum. Our results show that, in this context, WIMPs as candidates for dark matter can work well both on large scales and on subgalactic scales.     

Superweakly interacting massive particles

We investigate a new class of dark matter: superweakly interacting massive particles (super-WIMPs). As with conventional WIMPs, super-WIMPs appear in well motivated particle theories with naturally the correct relic density. In contrast to WIMPs, however, super-WIMPs are impossible to detect in all conventional dark matter searches. We consider the concrete examples of gravitino and graviton cold dark matter in models with supersymmetry and universal extra dimensions, respectively, and show that super-WIMP dark matter satisfies stringent constraints from big bang nucleosynthesis and the cosmic microwave background.