Zhi-Gang Wang

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.

Performance Study for the CEPC ScW ECAL

The Circular Electron Positron Collider (CEPC) project is a Higgs/Z factory proposed by Chinese high energy physics community. A fine granular scintillator-tungsten electromagnetic calorimeter (ScW ECAL) is under development for the application of the particle flow algorithm (PFA) at CEPC. The active layers of the ScW ECAL are consisting of 5 × 45 mm2 plastic scintillator strips, with silicon photomultiplier (SiPM) readout. A set of ScW ECAL geometries has been implemented into the Geant4 simulation to optimize the geometry parameters such as layer numbers and scintillator sensor thickness. The performances of SiPM and the scintillator strip detector were tested, and the test results indicate that the SiPM and the sensor detector worked well. These results are meaningful for the construction and the tests of the prototype at the next stage.

A novel 2-dimensional cosmic ray position detector based on a CsI(Na) pixel array and an ICCD camera

A novel 2-D cosmic ray position detector has been built and studied. It is integrated from a CsI(Na) crystal pixel array, an optical fiber array, an image intensifier and an ICCD camera. The 2-D positions of one cosmic ray track is determined by the location of a fired CsI(Na) pixel. The scintillation light of these 1.0×1.0 mm CsI(Na) pixels is delivered to the image intensifier through fibers. The light information is recorded in the ICCD camera in the form of images, from which the 2-D positions can be reconstructed. The background noise and cosmic ray images have been studied. The study shows that the cosmic ray detection efficiency can reach up to 11.4%, while the false accept rate is less than 1%.