1991 Vol. 15, No. 6
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BaF2(La) crystal has been grown with 1% mole of BaF3 doped in BaF2 and the scintillation properties of the new crystal have been investigated before and after a γ irradiation of 60Co source.The radiation resistance of the domestic crystal can be up to a dose of 106 rad.Comparing with a pure BaF2 scintillator,it was found that the fast component of the BaF2(La) scintillator was almost no change but its slow component was suppressed to a factor of 4.
Using a silica aerogel sample with oxygen gas introduced as the positronium source,the γ ray energy from the parapositronium 2γ annihilation has been measured as 510998.7(2.5)eV by means of the comparison with the known γ energy 511856.2(2.3)eV of the 106Ru γ ray.The result,after a revision of the binding energy of positronium,is comparied with the adjusted value of the electron rest mass published in several years ago.
A small magnetic confinement device is reported.It is used to study the magnetically confined electron clouds supported by the Penning discharges.
Based on the general EFV method,with the constraints of time reversal invariance and axial symmetry,simplified formulas are deduced from the HFB transformation.These results make EFV a practical method in microscopic nuclear structure physics for describing arbitrary spin and parity states in both even-even and odd-odd nuclei,including states with various correlations.
We suggest that the heavy neutral lepton in a specific version of SU(3)L×U(1) model can not only act as dark matter but also provide with a source of anomalous positrons in the cosmic rays above 10GeV.
Two grand unified preon models with light quarks and leptons are presented.All these models have natural family structure at the composite level.One of them can give very low metacolor scale,ΛMC～104GeV.It is argued that the best choice for metacolor group is SU(4) and for unification group is SU(9).
We use the variationad method to study the meson states in the lattice Schwinger Model,and to calculate the mass ratio of vector and scalar mesons as well as the mass of vector meson.Our results are consistent with the exactly values in the continuum.
Based on variational method,we systematically studied the dynamical structures of A≤4 S shell Λ hypernuclei with the aid of the harmonic oscillator product expansions and the generalized Talmi-Moshinsiky transformation.We also made investigations on structures of the osdinary nuclei for A=2 and 3. By comparis on,we can see that the root mean distances between nucleons are shorten due to the presence Λ hyperon which compresses the core. Λ hyperon acts as the adhesive. The studies on internal structures of nuclear system show that the relative motions between particles are mainly in 0s orbits.
The Bjorken formula about maximal energy density in heavy ion collisions is modified,the effective way to increase the energy density is also analysed.The hydrodynamic equations and the equations of state in central and fragmental regions are discussed.It is pointed out that because of the energy diffusion caused by expansion of the system,it is lifficult to produce quark matter in fragmental region.For Au-Au collisions on the RHIC to be buict at BNL,the space-time region where phase transition occur d and the corresponding extent of impact parameter are predicted.
Based on the geometrical participant-model in RHIC the effect of secondary collisions is considered by introducing a phenomenological parameter.The rapidity distributions of Er and n of NA 35 and WA80 groups are fitted very well.The result shows that it is very important to include non-geometrical effects,such as secondary collisions on the basis of geometrical models.
The cross sections for 100Mo(n2n)99Mo,96Mo(n,p)96Nb and 92Mo(n,α)89m+gZr have been measured by using the activation method relative to the cross sections of 27Al(n,α)24Na in the neutron energy range 13.40—14.79MeV.The comparison between the values of measured and calculated using theory mode was made.The evaluated excition functions for the three reactions are given.
The nuclear matter density,collision number and entropy in the dynamic process of heavy ion collision 40Ca+40Ca at EL=400MeV/A for very central collision were calculated.The results show that the nuclear spatial density distributions depend mainly on the mean field but rarely on the nucleonnucleon collisions.The density distribution in the momentum space,collision number and entropy are influenced by the mean field and nucleon-nucleon collision,especially the medium effects.
The relativistic hydrodynamic equations derived from the energy-momentum conservation,are generalized to include the equation of the particle number.The influences of the latent heat and particle distribution on the spectrum are studied on the basis of the generalized formalism.It is shown that these influences should be included,in order to get a reasonable prediction for the formation of the quark matter.
By using the Generator Coordinate Method (GCM),the continuous variables representation of IBM (s,p,d) has been derived and discussed in this paper.The calculated splitting of giant dipole resonances (GDR) is close to 3MeV in deformed nuclei.The ratio of dipole strengths to the longitudinal and transverse components is less than 2.
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