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Having advantages of low capacitance and low energy threshold, the PC-HPGe (Point-Contact High Purity Germanium) detector has found its application in the direct detection of WIMP(Weak Interaction Massive Particle) in CDEX (China Darkmatter Experiment). The MSE (Multi-Site Event) and SSE(Single-Site Event) discrimination methods of the PC-HPGe detector are introduced in this article, including their physical basis, the electronics system and the algorithms to implement them. Behaviors of the PC-HPGe detector are studied intensively through this research and finally the experimental results of the LE discrimination method are presented.

The CDEX (China Dark matter EXperiment) Collaboration will carry out a direct search for WIMPs (Weakly Interacting Massive Particles) using an Ultra-Low Energy Threshold High Purity Germanium (ULE-HPGe) detector at the CJPL (China JinPing deep underground Laboratory). A complex shielding system was designed to reduce backgrounds and a detailed GEANT4 Monte Carlo simulation was performed to study the achievable reduction of γ rays induced by radionuclides and neutron backgrounds by D(γ,n)p reaction. Furthermore, the upper level of allowed radiopurity of shielding materials was estimated under the constraint of the expected goal. Compared with the radiopurity reported by other low-background rare-event experiments, it indicates that the shielding used in the CDEX can be made out of materials with obtainable radiopurity.

The effects of surface resistivity of the high voltage provider on the space dispersion of the induced charge of a prototype Resistive Plate Chamber (RPC) have been studied experimentally and theoretically. The results of both experiment and theory agree and confirm that a two-Gaussian function can be used to fit the dispersion of the induced charge of the RPC. It is shown that the Gaussian function with the narrower width is mainly due to the expansion of the avalanche charge in the gas gap of the RPC, and the Gaussian function with the larger width is due to the charge dispersion when it passes through the resistive carbon film. This will be useful in the RPC design when one wants to make an RPC with high position resolution.

The possibility to detect fast neutrons with a multi-gap resistive plate chamber (MRPC) has been investigated. To detect fast neutrons, a thin polyethylene layer is coated on the surface of electrode glass as a fast neutron converter. The MRPC detects the charged particles generated by neutrons via the (n,p) reaction on hydrogen. A prototype detector has been developed and tested on fast neutron sources in order to evaluate its performance: good agreement between experimental results and simulation has been achieved. A detailed description of the detector and the experimental test results are presented.

A new method to monitor the energy variation of a multi-energy electron linac by combining a Cerenkov detector and a CsI(Tl) detector is reported. The signals in the Cerenkov detector show an appreciable but different dependence on the energy of the electron linac from the traditional CsI(Tl) detector due to the particular response of the former to charged electrons with high velocity above threshold. The method is more convenient than the HVL (half-value layer) method which is commonly employed to calibrate the energy of an electron linac for real time monitoring. The preliminary validity of the method is verified in a dual-energy electron linac with 6 MeV and 3 MeV gears. Moreover, the method combining the Cerenkov detector and the CsI(Tl) detector is applicable to probe the X-ray spectrum hardened by the inspected material and may serve as a novel tool for material discrimination with effective atomic number in radiation imaging.

A prototype RPC with position resolution less than 1 mm has been produced and studied. Based on this RPC detector, the effect of the width of the integrated FADC time window on the position resolution of a RPC has been studied experimentally and theoretically. The results of theoretical calculation and experimental measurement have shown good agreement.

Six-gap resistive plate chamber (MRPC) prototypes with semiconductive glass electrodes (bulk resistivity ~ 1010 Ωcm) were studied for suitability in time-of-flight (TOF) applications at high rates. These studies were performed using a continuous electron beam of 800 MeV at IHEP and an X-ray machine. Time resolutions of about 100 ps and efficiencies larger than 90% were obtained for flux densities up to 28 kHz/cm2.

Multi-gap Resistive Plate Chamber (MRPC) is a new generation of gas detector with good timing and spacial resolution, whose technique is widely applied in some recent high energy (nuclear) physics experiments. In this letter, we report a long-strip two-end readout MRPC and its test beam performance. The measurements show that the long-strip performs a transmission line characteristic and the impedance is independent of the length of strip. The MRPC module we developed is presented to gain a timing resolution of ~80 ps and a spacial resolution of ~6.4 mm. The possible application of the MRPC is also discussed.

We have studied the light induced rapid thermal diffusion of boron atom in silicon. The samples were heated by the rapid thermal processor. We have carried out spreading resistance and deep level transient spectroscopy (DLTS) measurements. The impurity distribution profile is much shallower and steeper than that of conventional thermal diffusion and the diffusion depth can be controlled to 0.1 μm. Several peaks in the deep level transient spectra were detected and the density of these defects ranges from 0.5×1012 to 5.6×1012 /cm3. The passivation and annihilation of these defects have been studied. We have also made the planar diode whose diameter is 500 μm. The reverse current and the back breakdown voltage of the planar diode are 10-9 A and 80 V respectively.

The CBM time of flight wall is proposed to be built with MRPC technology. In the past few years we have successfuly improved the rate capability of MRPCs to CBM level. However, in a relative high particle multiplicity situation (over 20 kHz/cm2), multi-hit capability is one of the most demanding requirement of the detector. In a free running mode too many noise not only affect the performance of MRPC but also enlarge the data file or even damage the FIFO. So it is needed to develop low crosstalk and low noise MRPC to meet CBM-TOF requirement. Three strip-readout MRPC with or without shielding grounds were designed to study how to reduce noise and crosstalk of MRPCs. In this paper we report on the performance of three different structures of MRPCs named G-0, G-2 and G-3. Tests with cosmic rays were performed at Tsinghua University. The results show that MRPC G-2 can perform better than other two structures, the average cluster size of G-2 is lower than 1.28 strips and the noise level is below 0.5 Hz/cm2. The detection efficiency is over 98% and the time resolution is around 65 ps.