Zheng-Hua An

Neutron–gamma discrimination of CsI(Na) crystals for dark matter searches

Abstract The luminescent properties of CsI(Na) crystals are studied in this report. Using a TDS3054C oscilloscope with a sampling frequency of 5xa0GS/s, we find out that nuclear recoil signals are dominated by a very fast light pulse with a decay time of ∼20xa0ns, while γ-ray signals have a decay time of ∼600xa0ns. The study of n / γ separation shows that the rejection factor can reach an order of 10 −7 with a signal efficiency of more than 80% at an equivalent electron recoil energy of 20xa0keV or more, and the quality factors are ∼10 times smaller than that for CsI(Tl) crystals in the corresponding energy region. It is suggested that the wavelength of nuclear recoil and γ-ray signals is also different. Such a property makes CsI(Na) an ideal candidate for dark matter searches.

Experimental study of a THGEM detector with mini-rims

The gas gain and energy resolution of single and double THGEM detectors (5{times}5cm2 effective area) with mini-rims (rim is less than 10{mu}m) were studied. The maximum gain can reach 5{times}103 and 2{times}105 for single and double THGEM respectively, while the energy resolution of 5.9 keV X-ray varied from 18% to 28% for both single and double THGEM detectors of different hole sizes and thicknesses.All the experiments were investigated in mixture of noble gases(argon,neon) and small content of other gases(iso-butane,methane) at atmospheric pressure.

Fast light of CsI(Na) crystals

The responds of different common alkali halide crystals to alpha-rays and gamma-rays are tested in our research. It is found that only CsI(Na) crystals have significantly different waveforms between alpha and gamma scintillations, while others have not this phenomena. It is suggested that the fast light of CsI(Na) crystals arises from the recombination of free electrons with self-trapped holes of the host crystal CsI. Self-absorption limits the emission of fast light of CsI(Tl) and NaI(Tl) crystals.

Luminosity monitoring and calibration of BLM

The BEPC II Luminosity Monitor (BLM) monitors relative luminosity per bunch. The counting rates of gamma photons, which are proportional to the luminosities from the BLM at the center of mass system energy of the psi(3770) resonance, are obtained with a statistical error of 0.01% and a systematic error of 4.1%. Absolute luminosities are also determined by the BESIII End-cap Electro-Magnetic Calorimeter (EEMC) using Bhabha events with a statistical error of 2.3% and a systematic error of 3.5%. The calibration constant between the luminosities obtained with the EEMC and the counting rates of the BLM are found to be 0.84 +/- 0.03 (x10(26) cm(-2).count(-1)). With the calibration constant, the counting rates of the BLM can be scaled up to absolute luminosities.

Beam test of CSES silicon strip detector module

The silicon-strip tracker of the China Seismo-Electromagnetic Satellite (CSES) consists of two double-sided silicon strip detectors (DSSDs) which provide incident particle tracking information. The low-noise analog ASIC VA140 was used in this study for DSSD signal readout. A beam test on the DSSD module was performed at the Beijing Test Beam Facility of the Beijing Electron Positron Collider (BEPC) using a 400~800 MeV/c proton beam. The pedestal analysis results, RMSE noise, gain correction, and particle incident position reconstruction of the DSSD module are presented.

The radiation hardness test on CsI(Tl) crystals for BESIII

The radiation hardness of prototype CsI(Tl) crystals has been tested for the electromagnetic calorimeter for the BESIII detector of the BEPCII. Although samples made by one of the producers were found to be soft under irradiation, the problem was quickly improved when this information was fed back. All the tested crystals were found to meet our requirement. At the same time, the monitor function of LED-Fiber system of BESIII EMC was verified.