2001 Vol. 25, No. 4
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With the Yangbajing AS γ array, the time variation of 10TeV cosmic ray was studied. Solar time semi diurnal and diurnal variations have been detected with 10.4σ and 9.6σ levels for the 10TeV cosmic ray flux and semi diurnal variation with an amplitude 0.13% and a phase 0.2 and diurnal variation with 0.075% and 0.12. The sidereal diurnal variation for 10TeV cosmic ray was not found with 0.7σ level. The analysis result in longer period gives some evidence of 7 days variations.
The total cross sections of γγ→γZ process for γγ c.m.s. energy 91.2—2000GeV are presented. W loop contribution is dominating when γγ c.m.s. energy is larger than 140GeV. The total cross section has a maximum, 220 fb(|cosθ|
In topcolor-assisted multiscale technicolor (TOPCMTC) model.we calculate the corrections of Pseudo Goldstone bosons (technipions,top-pions)to the cross section of the process qq→tt at the Fermilab Tevatron.Our results show that the corrections mainly come form top pions.With reasonable value of the parameters.the correction can increase the total tt production corss section σtt by as much as 17%.This may provide a window to detect tpo-pions.
By means of devices of geometry algebra the general decomposition of gauge potential (spin connection) on a compact n-dimension Riemannian manifold has been studied in detail. A general decomposition formula of SO(n) gauge potential in terms of a unit vector field on the sphere bundle has been established. Using same local structure between SO(2) and U(1), SO(3) and SU(2) the general decomposition formula of U(1) and SU(2) gauge potential in terms of the unit vector field has been also given respectively.
In order to treat the waste material of nuclear power and develop new type of clean nuclear power,it is necessary to measure the neutron adta of long half life nuclei existed in the waste material.The prompt spontaneous neutron spectrum is one of the most important unclear data for new type nuclear power facilities as well as for understanding the mechanism of fission neutron emission.The measurements of 248Cm/252Cf spontaneous prompt fission neutron spectrum in the neutron energy range form 200keV to 12MeV wer performed by using TOF method.A micro-ionization chamber aws used as fission fragment detector and stibene crystal as neutron detector.The flying paths of neutrons for the measurements were 30cm,50cm and 100cm respectively.The spontaneous prompt fission neutron spectrum of 248Cm was fitted by the Maxwellian distribution and the temperature was determined as (1.401±0.006)MeV in the corresponding neutron energy range.
Relativistic Hartree-Fock (RHF) theory has been adopted to describe properties of exotic nuclei. In order to investigate the contribution of Fock term and isovector mesons to the properties of exotic nuclei and to avoid effective interaction which is not unique, the density dependent relativistic Hartree (RDH) and relativistic Hartree-Fock(RDHF) theories with parameter free have been extended to describe the properties of exotic nuclei. The properties of Calcium isotope chain are calculated in the RDH and RDHF approaches, and the contribution of the Fock term and isovector mesons to the properties have been investigated particularly. It turns out that the influence of the Fock term and isovector mesons on the properties of neutron very rich nuclei, such as binding energies, RMS of neutron radius and distribution of neutron density, is very different from those of stable nuclei. We also briefly discuss importance of study on the properties of nuclei near drip line and the theoretical model used in this paper.
Two different rotational formulae for description of normal deformed and superdeformed nuclei are submitted by the definition of the softness and by two different representations of quantum algebra.With SD formula,near 80 SD bands in A～190 and 150 regions are calculated.The results show that the E2 γ-ray energies are fitted in high quality,and the phenomena of the turnover in dynamical moment of inertia can be also reproduced well.
The ground state properties of Ca isotopes far from stability line were systematically studied using the Skyrme Hartree Fock model.The shell effects on the binding energy and two neutron separation energy are discussed.The isospin dependency of the unclear radii and nucleon density distributions and the shell effects on these properties are also studied.It is shown that the neutron magic number affests the width of nuclear surface and the nucleon density distributions beyond the nuclear surface.The change of proton rms radii Rrms with neutron number excess I=(N-Z)/A follows Rrms=3/5(1+αI+βI2)rpZ1/3.The effect of the centrifugal potential on the nuclear density in the outer trach of nuclear surface is clearly shown.
The rotational collective flow in reactions of 58Fe+58Fe and 58Ni+58Ni at 40 MeV/u for different impact parameters was studied within the framework of IQMD model, by analyzing the mid rapidity azimuthal distribution and calculating semi-quantitatively the rotational observables. A strong isospin dependence of rotational collective flow has been found, namely, the more neutron-rich system exhibits stronger rotational collective flow. This isospin dependence is more appreciable in semi-peripheral collisions, and it mainly results from the isospin dependence of N-N cross section and the symmetry energy. Meanwhile, it is indicated that the rotational collective flow depends strongly on the impact parameter, namely, it increases with increment of impact parameter from near central to peripheral collisions and then decreases, finally disappears in the most peripheral collisions.
Based on the isospin dependence of quantum molecular dynamics with momentum dependent interaction, the dependence of symmetrical potential and isospin dependence of inmedium nucleon-nucleon cross section on the nuclear stopping were studied in wider beam energy region (45—150MeV/u) for four colliding systems with different ratios of neutron-proton.. The calculation results show that the nuclear stopping depends strongly on the isospin dependence of in medium nucleon-nucleon cross section σiso and weakly on symmetrical potential Usym for the all of colliding systems in wider beam energy region studied here. It is suggested that the information on the isospin dependence of in-medium nucleon nucleon cross section could the extracted from the comparisons between the theoretical results and the experiment data on the nuclear stopping in the process of intermediate energy heavy ion collisions. The dependence of the nuclear stopping on σiso is very sensitive to beam energy EL, and impact parameter b. The results also show that the effect of momentum dependence interaction on the nuclear stopping is important.
Several fitting methods that are applied on the γ spectrum to determine the light output of low light yield scintillators were compared with Monte Carlo simulation and real data. Deviations of the light yield to fitting values from different methods are evaluated. The stability of the fitting methods in the cases of varying background and varying fitting range is also studied.
The compensation for transient beam loading effect requires that a modulated RF pulsed is fed to the accelerator. A new SLED system to be able to generate the modulated RF pulse in long pulse multi bunch linac is studied. The required waveforms of SLED input pulses are computed to generate RAMP and flat-top RF pulses. The optimization method of SLED parameters is formulated. The results of cold test coincide with the theoretical prediction. RAMP and flat top RF pulses are generated using SLED for the first time.
Sextupole magnets are usually used in beam analyzing systems with high resolving power, micro-beam systems and storage rings of high energy accelerators. It is well known that sextupoles are equivalent to the drift spaces under first order approximation. Therefore, this kind of optical elements is often used to correct the second order aberrations of beam optics systems. When it is necessary to calculate the third order aberrations of a system, or to correct the third order aberrations with octupole magnets, one should know the analytical expressions of the third order terms of sextupoles. In this paper, Lie algebraic methods were used in the analysis of relativistic particle trajectories in the sextupole magnets, and the solutions of third order approximation in the six dimensional phase spaces were obtained.
Polyethylene terephthalate (PET) and polycarbonate (PC) films were irradiated by S, Kr and Xe ions and were illuminated with ultraviolet light. The normalized track etch rate for PET and PC films etched in different condition was measured by conductometric experiments. It is shown that normalized track etch rate can be over 1000 for PET films, 2000 for PC films under optimized condition. TEM photographs of copper nanowires electroplated into nanoporous nuclear track membranes show that the narrowest wire diameter of copper nanowires is 20nm and that the pore diameter calculated by conductometric experiments is in agreement with the wire diameter measured by TEM when the pore diameter is over 30nm.
Based on existing cross-section data and general theories, a Monte Carlo computer program named NEUTRON for calculating non-ionizing energy loss (NIEL) and ionizing energy loss (IEL) of neutrons in materials was written. The amount of IEL & NIEL and their distributions irradiation induced by 1MeV neutrons and protons in common semiconductor material Si were calculated with NEUTRON and introduced TRIM95, respectively. These results were analyzed and compared with literatures.
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