THE INVESTIGATION OF THE HIGH DENSITY MULTIWIRE PROPORTIONAL CHAMBER AS A DETECTOR FOR NEUTRAL PARTICLES

This paper describes a position sensitive multiwire proportional chamber with effective area of 200×200mm². The chamber combining with multi-layer lead γ-ray converter form a high density multiwire proportional chamber γ-ray detector. The lead converter is made in auniformly arranged matrix of 0.9mm diameter holes on a 1.1mm pitch. For 511keV photons the detection efficiency is 5.6%, and the spatial resolution is 1mm. The detector has been used in the investigation of positron camera, it also offers possibility for X-ray detection.     

Effect of Anode Floating Voltage and its Applications in Characterizing Silicon Drift Detectors

Anode floating voltage is predicted and investigated for silicon drift detectors （SDDs） with an active area of 5 mm2 fabricated by a double-side parallel technology. It is demonstrated that the anode floating voltage increases with the increasing inner ring voltage, and is almost unchanged with the external ring voltage. The anode floating voltage will not be affected by the back electrode biased voltage until it reaches the full-depleted voltage （-50 V） of the SDD. Theoretical analysis and experimental results show that the anode floating voltage is equal to the sum of the inner ring voltage and the built-in potential between the p＋ inner ring and the n＋ anode. A fast checking method before detector encapsulation is proposed by employing the anode floating voltage along with checking the leakage current, potential distribution and drift properties.     

THE RESPONSE OF A 3×3 BGO DETECTOR ARRAY TO 0.5—21MeV PHOTONS

An array of 9 BGO crystals of 20×20×200mm³ equipped with photomultiplier readout was assembled and tested. Radioactive γ and neutron sources, (p,γ) reactions by low energy protons from Van de Graaff accelerator and (n,γ) reactions by thermal neutrons from nuclear reactor were employed to produce photons in the energy range from 0.5 to 21MeV. The energy response of the array is shown to be linear over the whole range. Data on the energy resolution follow an E^1/2 dependence at low energies, and deviate from it at 4.43MeV and higher energies. Results from the lateral energy deposition of showers were compared with the predictions of the Monte Carlo simulation and found to be in good agreement. Our study demonstrates the feasibility of calibration and monitoring of BGO electromagnetic calorimeter by means of radioactive sources and low energy (p,γ) reactions.     

BaF2 Scintillator Coupling with a Low-pressure Multistep Avalanche Chamber

We studied the properties of a UV light sensitive low-pressure multistep avalanche chamber containing pure TMAE vapour.The gain of two chambers with different constructure at various temperatures is measured.With pure TMAE vapour at 40°C the gain of one chamber was 4×10⁵,the time resolution was 4.1ns.Coupling the chamber with a 2×2×2.4cm³ BaF₂ scintillator we successfully observed the signal of ¹³⁷Cs γ-ray of 0.661MeV.     

STUDY ON RADIATION DAMAGE OF CHINESE-MADE HIGH-Z SCINTILLATION CRYSTALS

Radiation damage effects of several Chinese-made high-Z scintillation crystals have been studied on a ⁶⁰Co irradiation unit of 100KCi Results on small size BGO crystals irradiated by 60Co γ rays with various doses from 5×10³ to 7.5×10⁵rad are presented.The decrease in scintillation light output depends non-linearly on the dose applied and saturation effects above 5×10⁴rad have been observed.The spontaneous recovery of the light output can be described by the sum of at least three exponential functions.The radiation damage effects of small size BaF₂,CsI(Tl) and ZnWO₄ crystals at 5×10⁵rad were also investigated.Serious damage to BaF₂ has been found.Preliminary analyses indicate that this may be attributed to the inclusion of certain critical elements in the crystal.CsI(T1) after irradiation does not exhibit strong afterglow of noticeable coloration as were reported in the literature.     

Development of Yangbajing air shower core detector for a new EAS hybrid experiment

Aiming at the observation of cosmic-ray chemical composition in the "knee" energy region, we have been developing a new type of air-shower core detector(YAC, Yangbajing Air shower Core detector array) to be set up at Yangbajing(90.522?E, 30.102?N, 4300 m above sea level, atmospheric depth: 606 g/m2) in Tibet, China.YAC works together with the Tibet air-shower array(Tibet-Ⅲ) and an underground water Cherenkov muon detector array(MD) as a hybrid experiment.Each YAC detector unit consists of lead plates of 3.5 cm thickness and a scintillation counter which detects the burst size induced by high energy particles in the air-shower cores.The burst size can be measured from 1 MIP(Minimum Ionization Particle) to 106 MIPs.The first phase of this experiment, named"YAC-Ⅱ ", consists of 16 YAC detectors each with a size of 40 cm×50 cm and distributed in a grid with an effective area of 10 m2.YAC-Ⅱ is used to check hadronic interaction models.The second phase of the experiment, called"YAC-Ⅱ ", consists of 124 YAC detectors with coverage of about 500 m2.The inner 100 detectors of 80 cm×50 cm each are deployed in a 10×10 matrix with a 1.9 m separation; the outer 24 detectors of 100 cm×50 cm each are distributed around these to reject non-core events whose shower cores are far from the YAC-Ⅱ array.YAC-Ⅱ is used to study the primary cosmic-ray composition, in particular, to obtain the energy spectra of protons, helium and iron nuclei between 5×1013eV and 1016 eV, covering the "knee" and also connected with direct observations at energies around 100 TeV.We present the design and performance of YAC-Ⅱ in this paper.     

Study on the Muon Backgroud in the Underground Laboratory of KIMS

KIMS is a group aiming at the search for WIMP. In WIMP search experiment, the muon is one important background. We measure the muon flux in Yangyang laboratory where is located at 700m underground. The structure and performance test of muon detector is described. The analysis on muon hit position and angle distribution has been performed. The simulations of muon flux have been done. The muon flux in the laboratory is found to be about (7.0±0.4)×10^-8/s/cm²/sr.     

STUDY OF THE TIMING PERFORMANCE OF A LARGE AREA PLASTIC SCINTILLATION COUNTER FOR TOF MEASUREMENT

A large area plastic scintillation counter (80×10×1cm²) for TOF measurement has been made and the timing performance of this system has been measured. Various effects on the timing performance have been studied.     

Study of ψ(2S)Decays into pπ and KK

From a study of(2S)decays into vector-pseudoscalar final states,ρπ and KK*,based on a sample of 1.27×10⁶ produced (2S) events,we have set upper limits at 90% confidence level on the branching fractions into ρπof 3.6×10^－5, into K⁺K^*+c.c.of 2.5×10^－5,and into K⁰K^*0+c.c.of 1.2×10^－4.We find that all these decays are substantially suppressed relative to the corresponding J/ψ decays in comparison with PQCD predictions.Our results confirm the MARK Ⅱ measurements at an improved sensitivity level.     

MEASUREMENT OF THE ENERGY SPECTRUM OF PRIMARY COSMIC PAYS

The method and arrangement determining the energy spectrum of primary cosmic rays by measuring the Cerenkov radiation were described. The integral power index γ=1.80±0.11 of energy spectrum of primary cosmic rays wa measured at the energy range of 2.9×10¹⁴－4.0×10¹⁵eV.     

Computation of 7Be Electron-Capture Rate in the Solar Interior

Under conditions near the center of the Sun, it shows that ⁷Be atoms are completely ionized between R=0 to R=0.1217R_⊙. The newly calculated ⁷Be and ⁸B solar neutrino fluxes are about 4.00×10⁹cm^－2·s^－1 and 6.18×10⁶cm^－2·s^－1, while the corresponding predicted values of the standard solar model are 4.80×10⁹cm^－2·s^－1 and 5.15×10⁶cm^－2·s^－1,respectively. It will further increase the discrepancy between the observed and the predicted neutrino fluxes in Super Kamiokande neutrino experiment.     

Integrability of AdS3×S3 Superstring

From the κ symmetric action of IIB string in AdS₃×S³ background given by Rahmfeld and Rajaraman, we derive the equations of motion. Then using the twisted dual transformation which was introduced by Hou et al. We construct the flat currents, and hence conserved non-local charge with one free parameter, for the Green-Schwarz superstring in AdS₃×S³. Thus we show the AdS₃×S³ string is integrable.     

First evidence of ψ(2S)→Ω-Ω+

The decay ψ(2S)→Ω^-Ω⁺ is analyzed using 14×10⁶ ψ(2S) events recorded by the Beijing Spectrometer Ⅱ (BESⅡ) at the Beijing Electron Positron Collider (BEPC). Based upon events with no missing charged tracks and a satisfactory four-constraint kinematic t, we determine the upper limit for the branching fraction of ψ(2S)→Ω^-Ω⁺ to be 1.5×10⁴ at a 90% confidence level. By including events with one missing charged track, we are able to report the first evidence of an Ω⁺ signal with a statistical signi cance of 3.1|σ. The branching fraction of ψ(2S)Ω⁺ is determined to be (4.80±1.56(stat)±1.30(sys))10⁵.     

BETHE-SALPETER EQUATION FOR qq SYSTEM AND CALCULATION OF MESON SPECTRA

In this paper,an adequate form of qq Bethe-Salpeter (B-S) equation with one gluon exchange interaction and harmonic oscillator confining potential being taken into account has been derived,based on correct Gordon decompositions of the γ-matrices and a proper treatment for the fermion propagators in the equation.Furthermore,a Pauli-Schrodinger (P-S) equation including relativistic corrections has been established on the basis of the B-S equation by making use of relations between 4×1 components of the 16×1 B-S amplitude and a connection between the B-S amplitude and the P-S wave function both of which were found in the approximation of the order of p²/m².Calculations of meson spectra by employing the latter equation give a better agreement with the experimental data.     

A STRUCTURE MODEL OF STRATONS AND LEPTONS

A subquark model is proposed. According to this model, stratons and leptons are consisted of rishons T and V, which are multiplets of group SU_H(3)×SU_C(3)×SU_G(2)×SU(2)×U(1). Three generations of both stratons and leptons are obtained naturally. In this model, proton decay modes are μ^－e⁺e⁺ or e^－μ⁺μ⁺.     

Effects of Additional Vacancy-Like Defects Produced by Ion Impealations on Boron Thermal Diffusion in Silicon

The effects of additional vacancy-like defects on thermal diffusion of B atoms in silicon were investigated by using secondary ion mass spectroscopy. B atoms were introduced into silicon by 30keV B ion implantation at a dose of 2×10¹⁴cm^－2, while the additional vacancy-like defects were produced by two different ways. One was via 40 or 160keV He ion implantation at a dose of 5×10¹⁶cm－2 and followed by an annealing at 800°C for 1h, which produced a well-defined cavity band near the projected range of He ions. The other was via 0.5MeV F or O ion implantation at a dose of 5×10¹⁵cm^－2,which creates excess vacancy-like defects around the 1/2 projected range of F or O ions. Our results clearly show that the additional vacancy-like defects could suppress the boron diffusion during subsequent thermal annealing at 800°C for 30 min. The suppressing effects were found to depend on both the ion type and ion energy. The results were qualitatively discussed in combination with the results obtained by using transmission electron microscopy and Rutherford backscattering spectroscopy.     

THE SYMMETRY BREAKING OF THE SUPERSTRING-INSPIRED MODEL

By considering the one-loop radiative corrections,we discussed the symmetry breaking of a specific superstringinspired model based on the gauge group SU(3)_C×SU(2)_L×SU(2)_R×U(1)^′×U(1)^′′ We discussed phenomenologically the neutrino mass problem,and the value of the soft breaking parameters A,m and M at the scale Mx were given.     

ΛΛ,ΛΛγ and ΛΛπ0 Productions in J/ψ Decay

The channels of J/ψ decay into,ΛΛ,ΛΛγ and ΛΛπ⁰ are analyzed with 7.8×10⁶ J/ψ events collected by BES detector at BEPC Collider.The branching ratios for three channels and the angular distribution for the first channel are measured.The branching ratios are Br(J/ψ→ΛΛ)=(l.08±0.06±0.24)×10^－3,Br(J/ψ→ΛΛγ)－4(90% CL)and Br(J/ψ→ΛΛπ⁰)=(2.3±0.7±0.8)×l0^－4 respectively. The angular distribution for J/ψ→ΛΛ is dN dcosθ=N₀(1+αcos²0),α=0.52±0.33±0.13.     

Photoluminescence Study of He ions hot-implanted Sapphire After 208Pb27+ of 230MeV Irradiation

In the present work the photoluminescence (PL)character of sapphire implanted with He ions and subsequently irradiated with ²⁰⁸Pb²⁷⁺ of 1.1MeV/u was studied. Sapphire single crystals were implanted with 110keV He ions at 600K temperature to fluences ranging from (0.5 to 2)×10¹⁷ ions/cm², some of them were subsequently irradiated with ²⁰⁸ Pb²⁷⁺.From experimental results we found PL spectra peaks at 375nm, 413nm, and 450nm, and it's intensity gets maximum at fluence of 5×10¹⁶ He ions/cm². Also we found a new peak at 390nm after subsequent ²⁰⁸ Pb²⁷⁺ irradiation, which is possibly due to the crystallized sediment containing nano crystal Al₂O₃ appeared on the sample surface.     

TRIPLET TO SINGLET CONVERSION OF POSITRONIUM IN OXYGEN

Using a aerogel sample with introduced oxygen gas as a variable energy positronium source,the triplet to singlet conversion of positronium in the elastic and inelastic collisions between positronium atoms and oxygen molecules has been investigated with a time selecting energy spectrometer.We have found that the conversion cross section σ_0—p is proportional to 1/v for slow positronium in the elastic collisons,where v is the mean velocity of positronium,and for the inelastic processes,the cross sections are estimated to be σ_0—p=2.1×10^－17cm² and 6.6×10^－18cm² respectively at kinetic energies of positronium near two thresholds.