Wang Zhaomin

THE MEASUREMENT OF ENTROPY INDICES IN PP COLLISIONS AT 400 GEV/C

Abstract The entropy indices are calculated from the data of 400 GeV/ c pp collisions. The entropy indices are increased with decreasing average multiplicities of the final states.

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.

NON-THERMAL PHASE TRANSITION IN PP COLLISIONS AT 400 GEV/C?

Abstract Factorial moments are calculated up to order q =7 by the star integral method for the data of pp collisions at 400 GeV/ c . Multifractality is observed in hadroproduction supporting a cascading scenario of particle production. The intermittency indices φ q and the behavior of the function λ q =( φ q +1)/ q indicate a possible non-thermal phase transition and two different regimes of multiparticle production.

Comparison of two position sensitive gamma-ray detectors based on continuous YAP and pixellated NaI(TI) for nuclear medical imaging applications

Dedicated position sensitive gamma-ray detectors based on position sensitive photomultiplier tubes (PSPMTs) coupled to scintillation crystals, have been used for the construction of compact gamma-ray imaging systems, suitable for nuclear medical imaging applications such as small animal imaging and single organ imaging and scintimammography. In this work, the performance of two gamma-ray detectors: a continuous YAP scintillation crystal coupled to a Hamamastu R2486 PSPMT and a pixellated NaI(TI) scintillation array crystal coupled to the same PSPMT, is compared. The results show that the gamma-ray detector based on a pixellated NaI(TI) scintillation array crystal is a promising candidate for nuclear medical imaging applications, since their performance in terms of position linearity, spatial resolution and effective field of view (FOV) is superior than that of the gamma-ray detector based on a continuous YAP scintillation crystal. However, a better photodetector (Hamamatau H8500 Flat Panel PMT, for example) coupled to the continuous crystal is also likely a good selection for nuclear medicine imaging applications.

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.

Monte-Carlo simulation of a compact gamma-ray detector using wavelength-shifting fibers coupled to a YAP scintillation crystal

The production and transportation of fluorescent light produced in wavelength-shifting fibers (WSFs) coupled to YAP scintillation crystal is simulated using the GEANT4 codes. An advantage of the wavelength-shifting fiber readout technique over a direct readout with a position-sensitive photo-sensor is the reduced requirement for position sensitive photomultiplier tube photocathode area. With this gamma-ray detector, the gamma camera is small and flexible and has larger effective field of view and low cost. Simulation results show that a) a mean 12 of photons per 59.5 keV gamma ray interaction is produced in the WSF located nearest to the incident gamma ray, and a spatial resolution of 3.6 mm FWHM is obtained, b) a mean 27 of photons per 140 keV gamma ray interaction is produced and a spatial resolution of 3.1 mm FWHM is obtained. Results demonstrate the feasibility of this concept of a compact gamma-ray detector based on wavelength-shifting fibers readout. However, since the very low photoelectron levels, it is very important to use a photon counting device with good single photo-electron response to readout the WSFs.

Scintillation Characteristics of Doped PbWO4 Crystals

Emission spectra, longitudinal transmission and light output for the Sb-doped and Y-doped PbWO4 crystals are presented. Scintillation decay kinetics has been measured by using gate integration and the single photon counting method with blue and green filters. Radiation hardness has also been measured by using 60Co γ-ray irradiation under different dose rates and different dose rate profiles. The light yield and radiation hardness of the Sb-doped and Y-doped PbWO4 crystals are improved as compared to the undoped crystals and are suitable for the requirements of compact muon solenoid.

BUNCHING PARAMETERS AND CORRELATORS IN 400 GEV/C PP COLLISIONS

Abstract The multiplicity fluctuations of charged particles produced in pp collisions at 400 Gev/ c have been studied by means of the bunching parameters (BPs) and bunching correlators. The results show that the values of BPs η 2 ( M ) and η 3 ( M ) depend not only on the width of multiplicity distribution, but also on the phase space correlations. The BPs η 2 ( M ) and η 3 ( M ) follow the same power-law behavior indicating multifractal structure in pp collisions at 400 GeV/ c . The values of the second-order bunching correlators depend on the width of multiplicity distributions and decrease with increasing bin-bin distance D .

Angular dependence of particle correlations in pp collisions at 400 GeV/c

Abstract The angular dependence of the particle-particle correlation (PPC) and its asymmetry (PPCA) has been studied by using the experimental data of multiplicity production for pp collisions at 400 GeV/ c . The results differ strongly from the overall behavior of e + e − data, but agree with the results obtained by NA22 Collaboration quite well.