高纯锗探测器实验的可视化数据分析系统

高纯锗(high-purity germanium, HPGe)探测器是γ放射性分析的重要设备之一。HPGe探测器实验对于核学科人才培养至关重要。基于兰州大学核科学与技术学院HPGe探测器本科生实验教学需求，开发了基于LabVIEW的可视化数据分析系统。系统以可视化的编程方式完成HPGe探测器的效率刻度和能量刻度，能够实现对实验数据的分析与处理及实验结果的可视化输出，具有活度测量和未知源判断两种功能。系统界面清晰简洁、操作方便，丰富了实验教学模式，有助于激发学生的学习兴趣，提升实验课堂教学效果。同时，该系统在中子活化分析、核素分析、环境辐射监测等方面也具有一定的应用价值。     

HPGe 探测器晶体尺寸及效率的研究

采用蒙特卡罗方法模拟计算光子的探测效率需对高纯锗( HPGe ) 探测器进行准确的建模。模拟计算研究了HPGe 晶体长度对探测效率的影响,并在空间不同的测量位置对放射源进行测量,将模拟计算与实验测量相结合,对探测器晶体的尺寸进行调整,获得了HPGe 探测器晶体的模拟计算的准确尺寸,并在122s1 332 keV 能量范围内对模拟结果进行了验证。结果表明,在此能量范围内HPGe 探测器的探测效率的模拟计算值与实验测量值的相对偏差大多数在5% 内,并建立点源探测效率与探测器轴向距离的关系。The accurate shape of HPGe detector is needed in order to calculate its detection efficiency with Monte Carlo methods. In our calculation, the influence of the HPGe crystal size on efficiency has been investigated; the final crystal sizes were determined by comparison with experiments and were validated by the experimental efficiency obtained at several source-to-detector positions. The results show that when the crystal dimensions determined are used to calculate the detection efficiency in the energy range 122s1 332 keV, the relative deviations between simulated and most experimental results were within 5%. In addition, the relationship between detection efficiency and axial distance to detector was established.     

GROWTH TECHNIQUE OF MOLECULAR CRYSTAL OF NAPHTHALENE

A furnace for growing single crystal naphthalene of diameter 1-1.3cm and length up to15cm has been constructed by the Bridgman method in combination with zone-melting technique.The furnace is simple in its construction,convenient in its operation and convenient for the observa-tion of the crystal growth process.The effect of the shape of crystal growth container on crystalgrowth is discussed and the experiment in vapor growth of small naphthalene flakes is described.The preparation procedure of naphthalene samples for ultrasonic measurement,which may be alsouseful for preparation of other soft crystals,is given.     

重丰中子新同位素——238Th

利用兰州重离子加速器（ＨＩＲＦＬ）提供的６０ＭｅＶ／ｕ的１８Ｏ离子束照射天然铀靶,通过多核子转移反应生成２３８Ｔｈ．用快速放射化学分离技术从铀及其反应产物的混合物中分离出Ｔｈ同位素．使用两台高纯锗（ＨＰＧｅ）探测器测量了样品的γ射线活性,观测到了２３８Ｔｈ的β－衰变子体２３８Ｐａ的γ射线的生长、衰变行为,测定２３８Ｔｈ的半衰期为9.4±2.0min A new nuclide 238Th has been produced via multinucleon transfer reaction by 60 MeV/u 18 O ion irradiation of natural uranium. The produced thorium was radiochemically separated from the mixture of uranium and its reaction products. The activity of thorium was measured by using a HPGe detector and a planar HPGe detector. 238 Th has been identified for the first time by measuring the growth and decay of the γ rays from its daughter nucleus 238 Pa.     

Beam energy measurement system at BEPCⅡ

The beam energy measurement system at BEPCII is composed of there parts： laser source and optics system, laser-electron interaction system and High Purity Germanium （HPGe） detector system. The special components and construction of each part are introduced, especially about radiation background measurement in the storage ring, which is of great importance for the safe commissioning of HPGe detector.     

Ionization of Atoms and the Thomas－Fermi Model for the Electric Field in Crystal Planar Channels

The electric field in the crystal planar channels is studied by the Thomas-Fermi method.The ThomasFermi equation and the corresponding boundary conditions are derived for the crystal palanar channels,The numerical solution for the elctric field in the channels between(110) Planes of the single crystal silicaon and the critical angles of channelling protons in them are shown.Reasonable agreements with the experimental data are obtained.The results show that the Thomas-Fermi method for the crystal works well in this study,and a microscopic research of the channel electric field with the contribution of all atoms and the atomic ionization being taken into account is practical.     

Ultraviolet laser-induced voltages in LaSrAlO4 single crystal

Laser-induced ultrafast photovoltaic effect is observed in LaSrAlO4 single crystal at ambient temperature without any applied bias. An open-circuit photovoltage is obtained when the wafer is irradiated by a 248-nm-KrF laser pulse of 20 ns duration. The response time and full width at half maximum of the photovoltage pulse are 6 ns and 19 ns, respectively, indicating that LaSrAlO4 single crystal has potential application in ultraviolet detector.     

Optimum condition of efficiency functions for HPGe γ-ray detectors in the 121-1408 keV energy range

The optimum condition of three commonly used functions in the Genie 2000 γ spectra analysis software have been studied in the 121-1408 keV energy range. The three functions are applied for fitting the full-energy peak efficiency of the HPGe gamma-ray detector. A detailed procedure to obtain the optimum condition is described. The HPGe detector is calibrated at 11 cm by three radioactive sources of point form （^152Eu, ^137Cs, ^60Co） providing 11 energy peaks. After data processing, results shows that the three functions used in the Genie 2000 gamma spectra analysis software fit best at orders 3-5. Lastly the standard radioactive source 133Ba is chosen to validate the results. Differences between the standard activity of 133Ba and the result obtained from the fitting functions are below 1.5%. Therefore the optimum orders of the three functions used in the Genie 2000 3, spectra analysis software are 3-5 with the 11 energy peaks.     

Investigation of add-back effects in a segmented Clover detector

The resolution and the summing characteristics of an EXOGAM segmented Clover germanium detector has been studied for use it in y spectroscopic experiments. The measurements have been performed with standard radioactive sources of ^152Eu, ^133Ba and β-delayed γ-rays from 176Ir decay. The data analytic results, realized by software, are presented in this paper.     

Dedicated 4πβ(LS)-γ(HPGe) digital coincidence system based on synchronous high-speed multichannel data acquisition

A dedicated 4πβ(LS)-γ(HPGe) digital coincidence system with five acquisition channels has been developed. Three ADC acquisition channels with an acquisition resolution of 8 bits and acquisition rate of 1 GSPS are utilized to collect the signals from three PMTs which are used to detect β decay, and two acquisition channels with an acquisition resolution of 16 bits and acquisition rate of 50 MSPS are utilized to collect the signals from high-purity germanium(HPGe), which is used to detect γ decay. In order to increase the accuracy of the coincidence system, all five acquisition channels are synchronous within 500 ps. The data collected by the five acquisition channels will be transmitted to the host PC through a PCI bus and saved as a file. Off-line software is utilized for the 4πβ(LS)-γ(HPGe) coincidence and data analysis as needed in practical applications. Tests of the system show that system can record pulse signals from 4πβ(LS)-γ(HPGe) synchronously for further coincidence calculation and the highest coincidence rate of the system is 20 K/s, which is sufficient for most applications. Compared with traditional coincidence modules like MAC3, the digital coincidence system has a higher flexibility of coincidence algorithm. In addition, due to the use of ADC, the structure of the coincidence system is simplified. This paper introduces the design of the hardware, the synchronization method and the test results of this system.     

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.     

Measurement of photoelectron yield of the CDEX-10 liquid argon detector prototype

The China Dark Matter Experiment (CDEX) is a low background experiment at China Jinping Underground Laboratory (CJPL) designed to directly detect dark matter with a high-purity germanium (HPGe) detector. In the second phase, CDEX-10, which has a 10 kg germanium array detector system, a liquid argon (LAr) anti-Compton active shielding and cooling system is proposed. To study the properties of the LAr detector, a prototype with an active volume of 7 liters of liquid argon was built and operated. The photoelectron yields, as a critically important parameter for the prototype detector, have been measured to be 0.051-0.079 p.e./keV for 662 keV γ rays at different positions. The good agreement between the experimental and simulation results has provided a reasonable understanding and determination of the important parameters such as the surviving fraction of the Ar₂^* excimers, the absorption length for 128 nm photons in liquid argon, the reflectivity of Teflon and so on.     

Study on cosmogenic activation in germanium detectors for future tonne-scale CDEX experiment

A study on cosmogenic activation in germanium was carried out to evaluate the cosmogenic background level of natural and ~(70)Ge depleted germanium detectors. The production rates of long-lived radionuclides were calculated with Geant4 and CRY.Results were validated by comparing the simulated and experimental spectra of CDEX-1B detector. Based on the validated codes, the cosmogenic background level was predicted for further tonne-scale CDEX experiment. The suppression of cosmogenic background level could be achieved by underground germanium crystal growth and high-purity germanium detector fabrication to reach the sensitivity requirement for direct detection of dark matter. With the low cosmogenic background, new physics channels,such as solar neutrino research and neutrinoless double-beta decay experiments, were opened and the corresponding simulations and evaluations were carried out.     

Experimental and theoretical Compton profiles of Be, C and Al

The results of Compton profile measurements, Fermi momentum determinations, and theoretical values obtained from a linear combination of Slater-type orbital (STO) for core electrons in beryllium; carbon and aluminium are presented. In addition, a Thomas-Fermi model is used to estimate the contribution of valence electrons to the Compton profile. Measurements were performed using monoenergetic photons of 59.54 keV provided by a low-intensity Am-241 γ-ray source. Scattered photons were detected at 90° from the beam direction using a p-type coaxial high-purity germanium detector (HPGe). The experimental results are in good agreement with theoretical calculations.     

Dependence of energy resolution of a plane-parallel HPGe detector on bias voltage upon registration of low-energy X-rays

In this study, we theoretically analyze the processes in a plane-parallel high-purity germanium (HPGe) detector. The generating function of factorial moments describing the process of registration of low-energy X-rays by the HPGe detector with consideration of capture of charge carriers by traps is obtained. It is demonstrated that the coefficients of expansion of the average signal amplitude and variance in power series over the quantity inversely proportional to the bias voltage of the detector allow one to determine the Fano factor, the product of the charge carrier lifetime and mobility, and other characteristics of the semiconductor material of the detector.     

Method for developing HPGe detector model in Monte Carlo simulation codes

This paper describes a simulation model for a high-purity germanium (HPGe) detector by scanning the detector with a low-energy collimated source and calibrating the efficiency of the detector. The parameters of the initial simulation model, particularly the dead-layer thickness, were modified step by step according to the experimental results. The validity of codes, models, and methods was shown by implementing the model into the FLUKA and MCNPX codes and cross-checking against the experimental data.     

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.     

Simulated minimum detectable activity concentration (MDAC) for a real-time UAV airborne radioactivity monitoring system with HPGe and LaBr3 detectors

An automatic real-time UAV airborne radioactivity monitoring system with high-purity germanium (HPGe) and lanthanum bromide (LaBr₃) detectors (NH-UAV) was developed to precisely obtain small-scope nuclide information in major nuclear accidents. The specific minimum detectable activity concentration (MDAC) calculation method for NH-UAV in the atmospheric environment was deduced in this study for a priori evaluation and quantification of the suitability of NH-UAV in the Fukushima nuclear accident, where the MDAC values of this new equipment were calculated based on Monte Carlo simulation. The effects of radioactive source term size and activity concentration on the MDAC values were analyzed to assess the detection performance of NH-UAV in more realistic environments. Finally, the MDAC values were calculated at different shielding thicknesses of the HPGe detector to improve the detection capabilities of the HPGe detector, and the relationship between the MDAC and the acquisition time of the system was deduced. The MDAC calculation method and data results in this study may be used as a reference for in-situ radioactivity measurement of NH-UAV.     

Matrix formalism and singular-value decomposition for the location of gamma interactions in segmented HPGe detectors

Modern coaxial and planar HPGe detectors allow a precise determination of the energies and trajectories of the impinging gamma-rays. This entails the location of the gamma interactions inside the crystal from the shape of the delivered signals. This paper reviews the state of the art of the analysis of the HPGe response function and proposes methods that lead to optimum signal decomposition. The generic matrix method allows fast location of the interactions even when the induced signals strongly overlap.