1999 Vol. 23, No. 06
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We have studied the performance of a doublelayer TOF unit, which is made of two BC408 scintillators coupled direchy with high antimagnetic R2490-05 PMTs. The experimental results using a 2GeV π－ beam show that its time resolution is less than 50ps. With the good bine resolution, simple construction, mature technique and low price, the TOF detector composed of the unit studied herein is capable to be applied in the PID system in the τ-c factory.
The element distribuhons of intermediate mass fragments (IMF) emitted over an angular region of 5°—140° have been measured in the reachons of 30MeV/u 40Ar+58,64Ni and 115In. Within 20°—80° range the IMFs with Z=3-24 were observed. The IMF production cross section changes smoothly with its charge number,and the element distribuhon changes continuously when the IMF charge number increases across the charge number of the projectile. There is no strong dependence of the element distribution on the charge number of the projectile in this angular region.The transition nature of the reaction mechanism in the intermediate energy region and the power law of the IMF element distribution,as well as the dependence of element distributions on the threshold of the detectors were discussed.
Energy coherence widths of the dissipative products in the collision 27Al+27Al are extracted from measurement of the excitation functions. Then, the nuclear temperature T of the intermediate dinuclear system are determined, and discussed by using a concept of coherence rotation.
Produchon yields were determined for 25 abet fragments produced from the reaction of iron with 80 MeV/u 16O ions. From these data, charge distribution and mass yield distribution have been deduced. The experimental results are compared with those reported from our previous work. It is found that the width parameter σz and the most probable charge Zp of the charge distribution increase slowly with increasing bombarding energy. The mass yield distribution is discussed in terms of the concepts of limiting fragmentation and factorization.
The generators and irreducible representation coherent stato of the SU(1,1) group are constructed by using the inverse operators of hose harmonic oscillator, and the inhomogeneous inverse differential realizations of the SU(1,1) group are derived.
The production and absorption of J/ψ at SPS energy in p-A and A-A collisions have been simulated by using the General Cascade Program (GCP). Nucleon absorption mechanism and comover absorption mechanism are considered to investigare the J/ψ suppression. The results agree well with experimental data of J/ψ production,except for the data in Ph-Ph collision.
Although it has been verified that the interacting boson model (IBM) can be applied to light nuclei in sd shell successfully, the deficiency shll exists. The level of experimental spectrum of 24Mg is much higher than 3. The similar result can not be obtained by using of conventional IBM, in which only one-body and two-body interactions are concerned. Three-body interactions have been discussed by some authors, but the authers mainly considered the diagonal interactions. Moreover,the defect mentioned above can not be solved with these interactions. Introducing three-body non-diagonal interaction, the energy levels of 24Mg are calculated, the difficulty of low 0 theoretical level is overcome and the coincidence betWeen theory and experiment is improved. This work illustrates that in some cases the three-body non-diagonal boson interaction is important.
Deing the factorial moment analysis with non-integer partition M of phace space, the influence of the unflat distribution of two or more particle correlations has to be considered. In this paper the analysis method on the factorial moment in the phase space of multiparticle production with non-integer partition M is studied carefully.A systematic method for rectifying FM distribuhon with non-integer partition M is developed. The calculated results with this method is checked by using NA22 data.
Using modified surface delta interaction, the deformed Hartree-Fock calculations for twenty tWo nuclei: 102—114Ru, 102—116Pd and 104—116Cd are performed.Prolate and oblate configurations are obtained. The calculated results show that there exist form transitions and shape coexistence from mass number 102 to 116, and that the single-particle energy spectra are different not only for different mass number but also for different configurations of nuclei. At the same time, it is also found that the numbers of proton and the 3s1/2 orbit begining to fill with neutrons play important roles in the shape transitions.
Using a microscopic momenteum space optical potential and the method for treating the Coulomb force, which is propose by R Crespo and J. A. Tostevin, we calculated the differential cross section of elastic nucleon scattering from the 3H and 3He mirror nuclei at 500MeV and the ratio of cross sections. The charge symmetry breaking effects due to the Coulomb force between the proton and nuclei are shown.
The proton electrostatic accelerator, V2 completed in 1958 has been operated for 40 years. At present, the highest energy is 2.4 MeV. The intensity of the proton beam is 0.6-2.5μA. The stability of the power suPPly for the magnetic analyzer is ±0.01%. The energy resolution of the proton beam is ±0.1%. The arrangement of the equipotential rod along the charging belt was changed from the original design, the dismantiling and installing of the belt takes much less bine and labor. A three. forked vacuum pipe was installed, which can be used to extract external proton beams. ms accelerator is mainly used for nuclear analysis since the seventies. Recently the ionoluminescence (IL) method was used to study the chemical states of iron in a plagioclase sample with the external proton beam, both ferrous and ferric iron peaks (Fe2+, Fe3+) from the plagioclase sample were detected in the IL emission spectrum.
Highly oriented pyrolytic graphite (HOPG) samples were bombarded by Ar+8 ions with energy range from 10.1 to 112MeV. After bombardment the sample surfaces were observed using a STM and NanoScope. The resultS show that the energetic ion could cause observable praotrusionlike damage on the HOPG surface.The relationship betWeen damage and energy loss, and the possible mechanism of damage process are discussed.
The observation of underground multimuon phenomena is an important way for the study of the cosmic ray composition in the 'knee' region (1015-1016 eV). It is noticed that the existing underground detectors are not very ideal for the composihon study because they were originally designed mainly for other aims. A new approach having higher sensitivity for this study by observing multimuon events using a detector array in a shallower depth underground is presented.
Unknown isotopes 125Nd,128Pm,129Sm, 137Gd,139Dy and 139Tb were produced using enriched targets 92Mo,96Ru and 106Cd, respectively, bombarded by 36Ar ion beam with the energies of 165-180MeV from the SFC cyclotron of HIRFL. The six new nuclides were separated and identified by a He-jet combined with a fast-tape transport system as well as "p-γ" and "X-γ" coincidence measurements. Their half-lives were determined to be (0.60±0.15)s, (1.0±0.3)s, (0.55±0.10)s,(2.2±0.2)s, (0.6±0.2)s and (l.6±0.2)s, respectively. Energy spectra of β-delayed protons from 125Nd,128Pm,129Sm,137Gd and 139Dy decay were measured. Two γ-rays with the energies of 109.0 keV and 119.7 keV were assigned tO EC/β+ decay of 139Tb.
The infra-red renormalization properties of the O(N) model is studied to two loops. The calculation is done within a mass dependent renormalization scheme. The mass-dependent one-loop renormalization group coefficients are obtained and the tWo-loop coefficients are calculated in the infnad limit. We observe cancellations within the framework of field theory which make the tWo-loop beta-function coincide with the one-loop beta-function in the infra-red limit.
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