1997 Vol. 21, No. 4
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209Fr has been produced by irradiation of 197Au with 16O from SFC accelarator uia the fusion-evaporation 4n channel.The(EC+β+)decay of 209Fr has been studied by a He-jet tape transport system.The decay scheme is proposed for the first time based on γ-t,X-γ-t,γ-γ-t coincidece and γ-γ delay coincidence measurements,which takes account of 20 observed γ ray.Five members of low-lying states in 209Rn can be explained by the multi-plet [(210Rn2+)(νf5/2)－1].The branching ratio for(EC+β+) decay of 209Fr has been estimated experimentaly to be(3.0±1.5)%.
This paper measured the plateau curve,height of pulse related with bias voltage of silicon microstrip detector which was before and after exposed,and the leakage current as well as size of ‘black hole’after exposed
Two diferent kinds of neural network methods,BP and LVQ,are applied to the identification of e,μ,πparticles in BES experiment,and better results are obtained.The μ data samples used for training and tests are from cosmic events,e and π are strictly selected from real experimental data by very tight cuts.Although their momentum spectrums are non-uniform,interseting enough is that selection efficiencies given by BP test results are quite uniform in the whole momentum range.The results from LVQ is litle worse.It shows that BP is more powerful in pattern recognition than LVQ at least in this study.
Measurements of the angular distributions and yields of atoms sputtered from Ag target by bombardment with FeCl+,56Fe+ and 35Cl+ are reported.Large enhancement occurs in the measured Ag atom yield for FeCl+ projectile in comparison with the sum of the sputtering yields for 56Fe+ and 35Cl+ bombardment at same impact velocities.The enhanecment can be explained by a model of the thermal spike-evaporation plus surface topography effect.
In topcolor-assisted technicolor scheme,we calculate the correction of the neutral color octet PG boson P0a to top quark production at the Tevatron.The result is that the PG boson P0a can significantly enhance the top quark production cross section.
We discuss a category of stable dark matter particles which are weakly interacting and related to the superstructure of the universe.These particles may be degenerate fermions and the bosons near a high temperature state.In both cases,we deduce that the particle mass is ～10－1eV and the absolute value of its chemical potential is <<10－1eV.This result is not in contradiction with the dip phenomena of the ultra high energy primary cosmic ray spectrum at ～1015eV and ～1018eV.
Using thermo-field edynamics method,we calculate the efective mass and Debye screening mass of the gluon at finite temperature and finite density.The critical temperature and density for the dissociation of J/ψ and ψ′are obtained.
Using the“con ealgorithm”in QCD to identify jet,the hard and soft processes in high energy hadroncic olisions are analysed indetail.A Monte Carlo simulation event sample is produced by PYTHIA.The resultant pseudorapidity distribution of jets has a plateau in the central region.The particle and transverse energy density in jets decreases exponentially with the increase of the distance from particles to jet axis.Through comparisons,we find the event average transverse momentum or maximum transverse momentum is positively correlated with multiplicity for the whole event sample,and negatively correlated with multiplicity for jet event subsample.Two ratio variables well describe the hardness of jet events,and they are positively correlated with the event average transverse momentum and negatively correlated with multiplicity,which confirms the event average transverse momentum is a better characteristic quantity to describe the hardness of jet events than multiplicity.
With a density-,temperature-,and momentum-dependent mean field,five diferent phases of nuclear equationo fstate:the gas,liquid,super heated liquid,supercooled gas and mechanical instability of spinodal phase for 197Au are described.Afterperforming a simulation in real space and in momentum space for these diferent phases at finite temperature T=6MeV,all kinds of nuclear clusters are sorted by using the coalescence model.Correlation analysis of the nuclear clusters demonstrates that multifragmentation pattern only comes from the mechanical instability of spinodal phase.
The dynamical calculation of quasi-fission reaction induced by 10.6MeV/u 84Kr on 27Al is performed using one-body dissipation model.The calculation suggests a fission time larger than 200×10－22 sec.It is found that the threshold for emergence of quasi-fission in the reactoin system is 8MeV/u.
In the nuclear pair shell model(NPSM),it is found that the“realistic”pairs of the valence proton and valence neutron can be used as the building blocks for many-body wavefunction,and the contribution from particle energy term H0 can be taken into account naturaly.It is also found that the NPSM is reduced to the fermion dynamical symmetry model and the interacting boson model in some special cases.
The relationship between the Gerasimov-Drell-Hearn(GDH)sum rule and the first monent,ΓP-the proton spin dependent structure function integral,is established.According to the sum rule and quark structure model of baryon,[SUsf(6)⊙O(3)]⊙SUc(3),the spin problem of the proton is discussed The present theoretical results are also compared with the data measured by EMC and SLAC groups.Our prediction is in good agreement with the data.We find that the P33(1232)photo-cxcitation dominates the spin structure function integrals and contributes negatively at low momentum transfer.At higher momentum transfer,the contribution of the P33 is positive,and it decreases rapidly as Q2 increasing and finally becomes negligible The integral changes its sign from negative into positive at about Q2=0.3GeV2.
A simulation of electron cooling process for the heavy ion beam in the proposed HIRFL Cooler-Storage Ring(HIRFL-CSR)is performed by taking into account the betatron and synchrotron oscilations of single particle.The continuous evolution of ion beam emittances and relative momentum spread are shown.Some factors that influence the cooling speed,like the space charge effect of electron beam,the dispersion in cooler section and the electron beam transverse temperature are presented.
Thi spaper describes thedesign,simulation and experiment of a multi-cavity RF gun with thermionic cathode for BFEL.This RF gun consists of 1/2+3 cavities (its first half cavity is about 1/3 of a full cavity) with a axis coupling bi-period standing-wave accelerating structure,and works at π/2 mode,2856MHz.We shortened the length of the lst cavity and added a short drift between the 2nd and 3rd cavities,so that the power of back bombardment electrons was greatly decreased and the logitudinal properties were adjusted properly.
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