2002 Vol. 26, No. 10
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The excited states of 169Re have been investigated by means of in beam γ-ray spectroscopy techniques with the 144Sm(28Si, 1p2nγ)169Re reaction. X-γ and γ-γ-t coincidences, DCO ratios and intra-band B(M1)/B(E2) ratios were measured. A strongly coupled band based on the 9/2－ Nilsson state and a decoupled band built on the h9/2 intruder proton orbital (nominally 1/2－) have been established. Their configurations are proposed on the basis of B(M1)/B(E2) ratios and by comparing the band properties with known bands in neighboring odd proton nuclei. The neutron AB crossings are observed at ω=0.23 and 0.27 MeV for the π9/2－ and π1/2－ bands, respectively. Band properties of the neutron AB crossing frequencies, alignment gains and signature splittings are discussed, and compared with those in the heavier odd-A Re isotopes.
Using R scan data collected at BESⅡ detector, we study the character of beam-associated background. We use the method of f factor and the fitting of event vertices to subtract the residual beam-associated background. The difference between the R values obtained by using these two methods is between 0.3% and 2.3%.
In the context of topcolor assisted technicolor(TC2) models,we calculate the contributions of the top Higgs h0t to e+e－→c eν e and compare the results with that of h0t to the processes e+e－→ Zh0t→Zc and e+e－→γh0t→γc. We further discuss the signals of these process at high energy e+e－ collider (LC) experiments. We find that e+e－→c eν e is very sensitive to h0t,which can be easily detected via this process in the future LC experiments with s=500—1500GeV,as long as its mass below the t threshold. The processes e+e－→Zc and e+e－→γc can also be used to detect h0t in the future LC experiments with s=500GeV.
In the framework of the relativistic covariant tensor formalism,the effective vertices for decay process J/ψ→pω with various intermediate N* states are studied carefully,and the corresponding amplitudes are derived. By performing Monte Carlo simulation,angular distributions pω(ω) invariant mass spectra and Dalitz plots for various partial waves in the J/ψ→pω process are obtained. It can be found that different partial waves give distinguishable distributions.
Excited states of 142Ce,populated in deep inelastic reactions of 82Se projectiles bombarding 139La target,have been studied to medium spins using in-beam gamma spectroscopy techniques. Three new levels have been identified at 2625,2995 and 3834keV,and assigned as 8+,9(－) and 11(－),respectively,based on the analysis of the properties of gamma transitions. These new yrast states follow well the level systematics of N=84 isotones. Their structures have been discussed with the help of empirical shell-model calculations.
The energy levels of odd A Tm isotopes in A≈160 region are calculated using the particle plus triaxial rotor model. The low lying bands of the isotopes are fit well by changing the energy gap and Coriolis attenuation factor. A possible relation between energy gap and neutron number is presented.
The neutron measurement system based on the Nuclear Pumped Laser (NPL) techniques was explored in this work utilizing the relationship between the neutron flux and the NPL laser power. Following the studies on the mechanism of the NPL, the laser intrinsic efficiency and the energy deposition efficiency in the laser cell of this system were theoretically studied in detail. A laser pumping mechanism was proposed. The variation of sensitivity with working time and the response function on neutron flux was discussed. The feasibility of this neutron measurement system was demonstrated theoretically.
By using color dipole model, the ratios of the p-A Drell-Yan cross section per nucleon for an 800GeV proton beam incident on Fe and D targets are calculated in the target rest system. It is shown that our calculations can quite well fit the E772 data with considering the nuclear shadowing effect in p-A Drell-Yan process and without the energy loss effect in it.
The structures of (ΩN)LST systems are studied in the SU(3) quark model,in which the coupling between quark antiquark and the meson fields is included. A resonating group method (RGM) calculation shows that (ΩN)0212 could be a bound state with considerably large binding energy,when the mechanism of s(s) annihilation to K* is considered.
The structures of the nuclei on the alpha decay chain of 271110 are investigated using self-consistent relativistic mean-field (RMF) model. The calculated alpha-decay energies are in good agreement with experimental data. The theoretical lifetimes reasonably agree with the data. The properties of 275112 are predicted. A discussion on the deformed shell around Z=108 is made.
The hyperon rms radii in Λ208Pb and neutron star structure have been studied in the framework of the relativistic mean field theory with nucleons,hyperons and mesons. Attention has been paid on the hyperon coupling constants which can not be accurately determined experimentally. A new relation between the hyperon rms radius in hypernucleus and the properties of a neutron star is proposed,i.e.,the larger the hyperon rms radius,the larger the maximum mass and radius of the star. Further accurate measurement of the hyperon rms radius in Λ208Pb will have important implications for the structure of neutron stars.
The thermal properties of nuclear matter are studied in the chiral effective Lagrangin in medium with BR scaling based on the framework of the relativistic mean field theory. The basic nuclear properties are reproduced. The mechanical and chemical instabilities are calculated and the phase diagrams are obtained.
Based on the quantum molecular dynamics model, the dynamical behaviors of the Liquid-gas phase transition in nuclei are investigated. In order to explore the characters of the Liquid-gas phase transition in the vicinity of the "critical point", the Maximum Lyapunov exponent (MLE) is employed and the method of calculation of the MLE is developed. The dependence of the mass distribution of fragments, density fluctuation and the MLE on temperature has been studied for nuclear systems 124Sn and 208Pb. As the main results, we have found that for heavy nuclear systems the MLE and the density fluctuation reach the maximum values at the same temperature, in which the maximum liquid-gas coexistence region is also found from the mass distribution of fragments.
Using a hadron and string cascade model, JPCIAE, and the corresponding Monte Carlo events generator, the energy and centrality dependences of charged particle pseudorapidity density in relativistic nuclear collisions were studied. Within the framework of this model, both the relativistic pp experimental data and the PHOBOS and PHENIX Au+Au data could be reproduced fairly well without retuning the model parameters. This paper shows that since
With the 58 million J/ψ data taken at BESⅡ in the last two years, a good particle identification (PID) becomes more important in data analyses. Since BESⅡ TOF is an important subsystem for PID, it is necessary to study TOF time and its resolution in detail. Using the 58 million J/ψ data we have studied the corrections for TOF time offset and its resolution, and finaly given out the correction result and PID efficiency.
To investigate the higher order mode (HOM) damping in the LHC 200MHz capture cavity when using four HOM couplers, simulations have been done by both frequency domain and time domain methods. Using these methods the impedance spectra of the higher order modes in the cavity before and after damping has been obtained. From this, detailed information about the HOM coupler's contribution to HOM damping can be obtained. The distribution and magnitude of some potentially dangerous higher order modes in the LHC capture cavity have been found.
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