Xu Zi-Zong

A high dynamic range readout unit for a calorimeter

A high dynamic range readout system, consisting of a multi-dynode readout PMT and a VA32 chip, is presented. An LED system is set up to calibrate the relative gains between the dynodes, and the ADC counts per MIPs from dynode 7 are determined under cosmic-ray calibration. A dynamic range from 0.5 MIPs to 1 x 10(5) MIPs is achieved.

THE INFLUENCE OF AVERAGE PHOTON NUMBER ON THE MEASURED FLUORESCENCE DECAY TIME OF SCINTILLATOR

Abstract Measurement of the light decay time by the delayed single-photon coincidence method requires that the average number of photons detected by photomultiplier tube be much less than one. The probability that multiple photons will be detected during the measurement always exists and makes the measured time decay spectrum appear to be faster than the true one. By using the probability density function of detected fluorescence photon, Monte-Carlo simulations and numerical calculation, the quantitative relationship between the deviation of measured fluorescence decay time and the average photon number is obtained. It is found that the deviation is directly proportional to the average photon number and inversely proportional to the time range of TAC. The methods to determine the average photon number are discussed.

Study of linearity for a high dynamic range calorimeter

A high dynamic range calorimeter has been designed for the DArk Matter Particles Explore (DAMPE) satellite. It consists of 308 BGO crystals, multi-dynode readout PMTs and front end electronics system. We have built on previous research to show that BGO fluorescence should not be saturated by high electron energy density under DAMPEs energy range. A BGO fluorescence simulator is set up to calibrate the energy range of the dynodes, while a cosmic-ray unit is used to calibrate 1 MIP with the ADC count in dynode 8. Linearity is achieved for the dynamic range from 0.5 MIPs to 1.26×105 MIPs. The requirements of DAMPE can thus be satisfied.

Delay line readout of a large dimension multi-wire proportional chamber

A two dimensional multi-wire proportional chamber with delay line readout was developed, which has a large sensitive area of 30 cm × 30 cm. Two cathode planes using printed circuit boards are orthogonally placed to give two coordinates of the impact point of the particle. Signals collected from the cathode strips are amplified and discriminated from two ends of the delay line at each cathode board. By recording the time difference between the two discrimination pulses and the common gate pulse from anode wires, a coordinate position was reconstructed, and a position resolution of better than 1 mm could be obtained in the whole sensitive area along the anode wires.

Micromegas prototypes with thermo-bond film separators

In this paper we report the results of Micromegas prototypes constructed by attaching micromesh to an anode using thermo-bond films. The excellent metal attaching ability and good dielectical property of this kind of film make it a promising material to be used as avalanche gap spacers. Several prototypes are successfully made. The electron transmission properties are first studied and then the gas gain is measured in argon-isobutane mixtures. The maximum gain of more than 104 is easily obtained. The energy resolutions for 55Fe 5.9 keV Kα ray can be better than 20% over one magnitude in gain for different operational gas mixtures and the best energy resolution of 13.7% (FWHM) can be achieved with the gas mixture of 94% argon concentration. The preliminary test results of the prototypes with sensitive area of 45 mm×45 mm without internal support show good uniformity across the sensitive area.

Study of the characteristics of a scintillation array and single pixels for nuclear medicine imaging applications

By using a pixelized Nal(Tl) crystal array coupled to a R2486 PSPMT, the characteristics of the array and of a single pixel, such as the light output, energy resolution, peak-to-valley ratio (P/V) and imaging performance of the detector were studied. The pixel size of the NaI(TI) scintillation pixel array is 2 mm?2 mm?5 mm. There are in total 484 pixels in a 22 ? 22 matrix. In the pixel spectrum an average peak-to-valley ratio (P/V) of 16 was obtained. In the image of all the pixels, good values for the Peak-to-Valley ratios could be achieved, namely a mean of 17, a maximum of 45 and the average peak FWHM (the average value of intrinsic spatial resolution) of 2.3 mm. However, the PSPMT non-uniform response and the scintillation pixels array inhomogeneities degrade the imaging performance of the detector.

Time characteristics of a self quenching streamer in the coexistence region

Abstract Experimental studies on the time correlation between electrical signals in the primary avalanche and optical signals which are emitted in the avalanches of the limited proportional mode and the self quenching streamer (SQS) mode have demonstrated that there exists a weak optical emission which is almost simultaneous with the limited proportional avalanche, that a streamer pulse in the SQS mode has a few nanoseconds delay relative to the primary avalanche, and that the spread of the delay (FWHM) is also a few nanoseconds.

Studies on decay time of fluorescence from a series of Ce-doped BaF2 crystals☆

Abstract Time distribution curves of fluorescence from BaF2 crytals doped with various concentrations Ce have been measured using a time spectrometer with time resolution of 680 ps FWHM. Fitting the experimental data to a multi-exponential function, the decay times and relative yields of fluorescence components are determined. Comparing these with the results of the emission spectrum excited by X-rays, some conclusions are drawn.

Evaluation of particle acceptance for space particle telescope

The particle acceptance instead of the G-factors has been introduced for a particle telescope. The particle acceptance of a telescope module TEST is simulated by using the GEANT4 Monte-Carlo package. The results are presented and explained.

3D simulation of micromegas detector performance

Micromegas (MICRO MEsh GAseous Structure) is a position-sensitive gaseous detector. It is widely used in particle physics. We present the results of full 3D Monte Carlo simulations of Micromegas performance, taking into account all the processes from the primary ionization, the elctron collection efficiency, and the gain to the signal formation. The simulation results are in good agreement with experimental data.