1993 Vol. 17, No. 8
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A systematic study of radiation backgrounds in the interaction region at the Beijing e+e－ Collider BEPC is carried out for the first time to the needs of particle physics experiment.An effective method to study dynamically the radiation environment of the collider is successfully developed which allows the measurement of the instantaneous radiation dose rate and is distribution for different beam conditions and as a function of time during a quiet luminosity run.The radiation sensitivity of domestic BGO and BaF2 crystals in the BEPC environment is examined.
Alternative layers of target material,which were prepared by evaporating 209Bi on the surface of mica foils,were irradiated with 12C ions.Ternary fission events in which three fragments of comparable mass were produced in 2525－47.5MeV/A 12C+209Bi reaction,were recorded by the mica detectors with 2π geometry.The observed probability ratio of ternary fission relative to binary fission in 2π geometry was modified to 4π geometry spatial in terms of the Monte Carlo method.The values of ratioes increase with the bombarding energy,and are compared with the calculation result of the cascade fission model.
We studied the density distribution of cathode induced charge on the radial cathode strips of the Incline Proportional Chamber.From the calculation we got the correction function for the center-of-gravity read out with 4 or 5 sampling strips and the position accuracy.Using 55Fe X ray we measured the spatial resoloution,the results agree with the calculation pretty well.
The effective potentials of 10-D supergravity model with one-loop Casimir corrections are derived in this paper.We show that compactification are unstable for Kalb-Ramond model,but in the case of ten-dimensional supergravity model it is possible to achieve a stable compactification by including the contribution of fermionic condensation.The relation of this kind of model with inflation cosmology is discussed.
Cyclic representations of quantum (super) algebras are studied at qp=1 using two methods:the quotient module method and the q-boson realization method.For the quantum algebras associated with any finite dimensional simple Lie algebra the general theory of two methods is given,and is generated to the quantum superalgebra Uqosp(1.2).By constructing the cyclic representation of q-Heisenberg-Wey1 superalgebras the q-boson realization method is generated to construction of cyclic representations of some high-rank quantum superalgebras.
A general parametrization of the symmetric KM matrix is given.The unitarity triangle is discussed,which embodies the unitarity of the symmetric KM matrix and CP violation.It is shown that the symmetric KM matrix is consistent with the directly measured values of the KM matrix elements,CP violation parameter │ε│ of K-K system,and B0d-B0d mixing parameter χd,provided the t-quark mass is large,mt≥160GeV.If │V12│=│V21│is confirmed by further experiments,KM matrix will turn out to be symmetric,so that a parameter is reduced in the standard model.
We have discussed the effect of valence quark mixing in DIS process.This effect,together with the pion cloud effect,dominates the violation of Gottfried sum rule.
In Lund model,the explanation of e+e－→qqg→3 jets and γ→3g→h's is based on applying Lund string fragmentation model to their assumed structures of colour string for qqg and 3g systems.In this paper,starting from the colour wave functions of qqg and 3g systems,we study these colour string structures by QCD directly.The results reveal the reasonableness and accuracy of Lund string pictures.
The anisotropy of the pion emission in the collisions of 1.8AGeV Ar+Pb is studied with the VUU model to obtain the information of the nuclear equation of state.We point out that the collective motion of pions in the final state has the final state has the characteristic similar to that of collective correlations of baryons,and the azimuthal anisotropy of pions is a sensitive parameter to the nuclear equation of state in the projectile rapidity region where the absorption of target spectator is weak.Collisions of 1.8AGeV Ar+Pb in the Bevalac streamer chamber are analyzed using the azimuthal correlation function for pions and the results favor the hard nuclear incompressibility.
In this paper the dilepton spectrum from an expanding hot nuclear matter is studied.Comparing with the spectrum from hot quark matter,we find that they are quite different.Especially the former with respect to the initial temperature or particle density is monotonic,the latter is non-monotonic.This may serve as theoretical examination for the production of quark phase transition.
It has been predicted that in nuclei with Z=52－56,there are many low-lying oblate and prolate rotational bands.Experimental investigation has been carrying out for the high spin band structure in serial I and Ce isotopes recently.It is found along with the prolate bands,there do exist oblate bands for proton h11/2,g7/2 and d5/2,configurations in I.The band termination (non-collective oblate shape) was found in 119,121I as well.All the prolate band structure was found in Ce.Further theoretical calculation was done with newly fitted Nilsson κ and μ parameters.Results show that the absolute values of shell energy and self-consistent pairing energy for oblate shape are always lager for I than for Ce.Besides,the band head oblateprolate energy difference is much in favor of oblate shape for I than for Ce.All these results are related to the existence of an oblate 54 gap in proton single particle diagram.
The contribution on the inelastic scattering spectra of discrete level part mainly comes from direct reactions.For the sigle-particle emission cross section calculated with the statistical theories,when the incident energy is less than 10MeV the main contribution comes from the equilibrium emission,but when the incident energy reaches 20MeV,more than 90% contribution comes from the pre-equilibrium emission.The contribution of the pre-equilibrium process to the second particle emission can be neglected when the incident energy is less than 20MeV and the contribution of the pre-equilibrium process to the third particle emission can be neglected when the incident energy is less than 50MeV.
The contribution of the fourth order exchange diagrams is first studied to the imaginary part of nucleon self-energy,the relativistic microscopic optical potential and the Schrodinger equivalent potential of the relativistic microscopic optical potential based on Walecka's meson-nucleon model.
The phase transition (PT) of a many-particle system with a close-shell configuration,the stability of the Hartree-Fock(HF) solution and the random phase approximation (RPA) are studied by means of a generalized three-level solvable model.The question whether the occurrence of an imaginery eigenvalue solution in RPA (OISA) may be considered as a signature of PT is explored in some detail,It is found that there is no close relation between OISA and PT.Generally,OISA shows that RPA becomes poor.
Applying the method proposed by C.M.Vincent and S.C.Phatak to p-3He elastic scattering,we studied the treatment of Coulomb interaction in momentum space.The differetial cross sections and spin observables at 500,400,300 and 200MeV are calculated.The present results are discussed and compared with previous results and experimental data.
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