1990 Vol. 14, No. 1
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The nature of the medium lifetime component of positron annihilation in Teflon (PTFE) polymer has been investigated by using a recently developed time-selecting γ ray energy spectro-meter with and without magnetic field.It has been assigned to o-Ps quenching annihilation too,just like the case of the longest lifetime component.
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.
In this paper,charge discs with variable radius are used in three-dimensional calculation for displacement and divergence of charged particles in all directions of motion,as well as the RMS emittance and emittance picture of the bunch in all phase planes.
In this paper,the rapidity distribution of quarks is further assumed to be a uniform distribution with the constraint of four momentum conservation.We apply Monte Carlo approaches to light quark jets.The semi-inclusive distributions and the multiplicity distributions in rapidity intervals are calculated.The characteristics of these distributions are discussed and the results are compared with the experimental data of average jets.
The comparison of two fragmentation schemes used in the analysis of e+e－ annihilation are presented in this paper.It is found that the independent fragmentation assumption is strongly disfavored by the data of the final particle multiplicities,and the string fragmentation assumption agrees with experiments.
The phase diagram of the lattice system of SU(2) gauge field coupled with the fixed length Higgs field in fundamental representation has been calculated by the variational-cumulant expansion method to the third order approximation.The method of determining the variational parameter has been improved by using the free energy to the second order approximation.Thus calculated phase diagram is in good agreement with the Monte Carlo estimation and the order of the phase transition is clearly determined in the third order approximation.
Considering that the IBM and IBFM cranking calculations in the lowest order of angular frequency can give reasonably good estimates for the moment of inertia,we extend them to study the dependence of the moment of inertia on the higher order terms.We find that the analytic expressions for the correction terms can be derived.Numerical calculations for 154Gd and 161Er are performed and compared with experiment.The Hamiltonian is taken from a microscopic approach.Calculated results show that the properties of higher order terms depend on the deformation of rotating system but the correction yields only limited effect when ω is small.
Based on the boson expansion and the so-called Jancovici-Schiff substitution,and approach has been developed to study the microscopic foundation of the interacting boson model.In this work an extension of the approach is made,thus one is able to treat the excitations of such system in which several neutron bosons,a proton boson and a proton-hole boson exist.With the consideration of the proton two-particle excitations we have studied the intruder quasi-rotational bands in double-even Sn nuclei.The Calculated results are compared with experiment and some features of the configuration mixture are discussed.
Based on the analysis of the mechanism of high energy nucleus-nucleus processes,the multisource model is further developed.The rapidity distributions are investigated by using the improved model.The calculated results fit the experimental data well.The physical origin of some characteristic features of the distributions is explained.
Excitation functions for the 21 products of the reaction induced by 16O on 115In have been determined in an energy region between 51 and 97MeV with nuclear chemistry techniques.The experimental results were compared with those calculated using Alice code and Monte-Carlo analogue.
A new ISOLAN facility has been constructed for on-line use with the heavy ion accelerator HIRFL in Lanzhou.The beam optical principle of an earlier ISOLDE type separator is modified by including a quadrupole doublet lens in front of the magnet.The mass spectra of Ar and Xe isotopes were measured with a scanner inside the collection chamber for an offline test.The resolution power is equal to 700—1200 by only using a single einzel lens.
By using the Hartree approximation which includes vacuum fluctuation correction in a model relativistic quantum field theory,it is found that the relativistic Landau parameters and the compressibility of the Fermi-liquid in the nuclear system,and the excitation energies of the giant monopole and quadrupole states are more close to the experimental values in comparison with the results of the mean-field theory.
In this paper,the elastic scattering of p+6Li is studied by 3QRGM,a three-cluster RGM omitting the antisymmetrization with the nucleon in the double magic cluster.The main conclusion from studying the systems of p+6Li and n+6Li is the following:The clustering and exchange effects lower the phase shifts conspicuously.hence they are very important in the lower energy region.
The α-clustering in a single-level model with pairing forces dependent of spin and isospin was discussed by means of the symmetry of the boson space in the Dyson representation of the Hamiltonian.The numerical results of the ground state energy,the separation energy of the last nucleon pair,and the α-transfer rates were given.
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