2004 Vol. 28, No. 10
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Associated with solar flare of 14 July 2000,a muon counting rate enhancement from a narrow sky window was observed by a shallow underground muon detector. This muon counting rate excess was very possibly caused by a directional solar proton beam produced in this flare. Starting from an incident solar proton beam at the top of the atmosphere, following with its interaction in atmosphere and propagating of the produced muons down to the underground detector,a full simulation was carried out in order to estimate the corresponding energies of primary protons and to deduce the upper limit on the flux of solar protons. From this work, for solar protons above 40GeV, under hypothesis of a power law index of -6,the integral flux upper limit is set to be 5.1×10-3/(cm2·sr·s)at 90% confidence level.
The differential cross section of e+e-→ωπ0 and the decay rate of ω→π+π-π0 are derived, and a simulation program is coded for the generator of e+e-→ωπ0 taking account of initial state radiative correction with G.Bonneau and F.Martin's formulations. The consistencies of various distributions between data, MC and theory expectation for e+e-→ωπ0 process prove the correctness of the derived formulae and the simulations.
The flavour independence of the strong coupling is a fundmental property of quantum chromodynamics(QCD). The observable which can be employed to test flavour independence is the multiplicity of charged hadrons in jets originating from quark of light flavour. In this paper we calculate the average of charged particle multiplicities in light flavour quark jets in e+e-→q 00→h′s events. We find that in e+e-→q00→h′s events with different primary quarks, the average production probability of uds quark. so the yields of directly production hadrons are related to the number of quark pairs. The symmetry of isospin and strangeness suppression factor etc are dependent on the flavor of prompt quark, and this dependence is more obvious in low energy region. But the final average multiplicities of charged particles seem to be equal in three kinds of light q0 jet events, which shows that our results are consistent to the predictions of QCD, i.e. the strong interaction is irrelevant to the quark flavor.
We obtain the ground state of the Hamiltonian which is constructed by general quadratic form of generalized coordinates and momenta. Consequently we can obtain eigenstates of each order energy. Invariant quadratic form with respect to coordinates under rotation subgroup G of SO(4) can be regularized as this kind of Hamiltonian, so we get the invariant ground state under rotation G. If G is a finite subgroup of SO(4),we will get the eigenvectors on noncommutative Orbifold R4/G.Based on this, we obtain the soliton solution on it.
After reviewing the Haldane's description about the quantum Hall effect on the fuzzy two sphere S2, we construct the noncommutative algebra on the fuzzy sphere S2 and the Moyal structure of the Hilbert space. By constructing noncommutative Chern Simons theory of the incompressible Hall fluid on the fuzzy sphere and solving the Gaussian constraint with quasiparticle source, we find the Calogero matrix on S2 and the complete set of the Laughlin wave function for the lowest Landau level, and this wave function is expressed by the generalized Jack polynomials in terms of spinor coordinates.
High spin states in 190Tl have been studied experimentally using the 160Gd(35Cl,5n) fusion evaporation reaction at beam energies of 167—175 MeV. A rotational band built on the πh9/2⊙νi13/2 configuration with oblate deformation has been established. Spin values have been firmly assigned to the πh9/2⊙νi13/2 oblate band by combining the present in beam experimental results with the complementary α γ correlation measurements of 194Bi α decay. With the configuration and spin parity assignments, the low spin signature inversion has been revealed for the πh9/2⊙νi13/2 oblate band. It is the first experimental observation of low spin signature inversion for a band associated with the oblate πh9/2⊙νi13/2 configuration. The low spin signature inversion could be interpreted in the framework of the quasiparticles plus rotor model including a J dependent proton neutron residual interaction.
In order to fit the total reaction cross section of exotic nuclei, by using Glauber model,we consider that the exotic nuclei is composed of a core and valence nucleon(s), the finite range correction has been added to the Glauber model, and a Fermi density distribution with two parameters has been chosen as the input density distribution of the core of the exotic nucleus for the special distribution of the valence nucleon(s), has a large dispersion. The results of the theoretical calculation are in agreement with the experimental one for nucleus with exotic structure, both at high and intermediate energy regions.
Within the supersymmetry scheme including many body interactions and a perturbation possessing the SO (5) (or SU(5))symmetry on the rotational symmetry, the superdeformed (SD) bands of the odd A nuclei in A≈190 mass region are investigated systematically. Quantitatively good results of the γ-ray energy spectra and the dynamical moments of inertia are obtained. It shows that the supersymmetry approach is powerful in describing not only the generic rotational property, but also the ΔI=4 bifurcation and the identical bands in SD states simultaneously.
By fitting the experimental data of total, nonelastic and elastic scattering angular distributions for n+Zr reactions, a set of neutron optical model potential parameters is obtained. The inelastic scattering angular distributions of discrete levels and double differential cross sections are calculated and analyzed by using the distorted wave Born approximation theory based on the unified Hauser Feshbach and the exciton model. With the fitting procedure the neutron induced level deformation parameters are obtained. The results indicate that the calculated results of the inelastic scattering angular distributions and total outing neutron double differential cross sections for n+ 90,91,92,94Zr can be obtained, which are all in good agreement with the experimental data.
Assuming a single proton 2p state structure of 13N, we study the halo like structure of 13N by calculating proton 13N elastic scattering at the incident energy of 1GeV in the framework of Glauber multiple scattering theory. The theoretical prediction of the differential cross section is obtained. Unlike 13C, there are no experimental data available at present to examine this prediction. However, the result could be a guide to the coming experimental measurement, particularly, for a possible experiment at the Institute of Modern Physics, the Chinese Academy of Sciences, Lanzhou, China. Recalling our previous theoretical prediction for 13C halo like structure and its experimental verifications, our present results evidently show that a possible halo like proton skin of 13N in ground state most likely exists. Therefore, an immediate experimental measurement of p-13N elastic scattering at the energy of 1 GeV is urgently demanded.
A brief introduction is given how to calculate the absolute intensities of γ rays arising from α decay. Examples are given to illustrate the applications of the calculation methods. The intensity balance and some discussion are also given in text.
The macroscopic deformed potential energies for fusion reactions are determined within a generalized liquid drop model (GLDM) which includes the volume—,surface,and Coulomb energies,the proximity effects,the mass asymmetry,and an accurate nuclear radius. In ordinary fission studies,it is assumed that the surface and Coulomb energies control the hight and width of the barrier. The surface energy ES takes into account only the effect of the surface tension force and does not include the contribution of the attractive nuclear forces between surfaces in regard to the neck or the gap between the nascent fragments. The nuclear proximity energy is adopted to take into account these additional surface effects in general liquid drop model. At the contact point,the proximity energy reaches maximum while it decreases both sides till to zero. The proximity energy decreases the barrier height by several MeV and moves the position of the barrier top forward,which corresponds to two separated fragments in unstable equilibrium by the balance between the attractive nuclear proximity force and the repulsive Coulomb force in the GDLM. It turns out that a wide macroscopic potential pocket in fusion process is formed due to proximity energy and appears at large deformation. This behavior does not appear at the barrier for the fusion reaction of light nucleus nucleus collision.
In the present investigation of high energy multiparticle production,the method of event by event ananysis has received wide interest. Inasmuch as the limited number of particles in a single event,an important problem is that the elimination of statistical fuctuations has to be worked out first of all. In the current literature,the elimination of statistical fuctuations has been only considered in lower order moments (not above the third order). In the present paper,the elimination of statistical fuctuations is studied in higher order moments and a general expression for the elimination of statistical fluctuations in the moments of arbitrary order is given.
The high flux of cosmic ray proton forms the main background of γ ray detection experiments using a lead scintillating fiber sandwiched electromagnetic calorimeter. The trigger scheme is studied to efficiently detect high energy γ rays and reject most of the proton events. Efficient cuts are derived from the Monte Carlo analysis of electromagnetic shower shape in the calorimeter. Photons with energy above 10GeV are triggered at the level of 99%. The requirement of proton rate less than 100 Hz is also satisfied. The accuracy of the simulations is testified with the beam test.
In order to identify the charge number Z of the projectile like fragments emitted from the dissipative heavy ion reactions,a set of ΔE-E telescope has been constructed,which consists of two ionization chambers for ΔE1 and ΔE2 in series followed by a position sensitive semiconductor silicon detector to deposit residual energy E. The trajectory of the incident particles is parallel to the direction of the electric field in the ionization chamber. The detector system has a lower energy detection threshold,compact configuration and capability against the disturbance from the electromagnetic wave. The charge resolution of Z/ΔZ≈30 of the telescope has been achieved in an experimental measurement of excitation functions of dissipative heavy ion reaction.
TeV GRBs are so far only searched by EAS arrays which typically have an angular resolution at about 1°. With the limited power in identifying γ ray events from proton background events,a search window in the size of angular resolution is often chosen in many experiments. In attempting to optimize the average search sensitivity,an analytic method to determine the window size is proposed and verified by Monte Carlo method in various conditions,including different signal,background intensities and different significance calculation methods. Finally,at the situation of low statistics,an empirical significance calculation formula seems to be possible.
A prototype of Resistive Plate Chamber with effective area of 490mm×490mm was built. The efficiency,output charge and time resolution were measured by cosmic muons when the detector was operated with F134a rich mixture in avalanche mode. The efficiency is higher than 95% with 2kV long efficiency plateau,the noise counting rate is less than 0.2 Hz/cm 2 and the time resolution reaches minimum when detector works in saturated avalanche mode. Relevant simulations and calculations were presented in this paper. The performances of RPC working in streamer mode were also tested.
The performance of a fine mesh photomultiplier tube (PMT)—Hamamatsu R5924(FM) to be used for the time of flight (TOF) counter in the upgraded Beijing Spectrometer (BESⅢ) was investigated in a strong magnetic field up to 1T. The dependence of the PMT relative gain on the magnetic field intensity at both 0°and 180°directions were measured. It was found that the relative gain of the PMT is reduced by a factor of 50 or more at 1T magnetic field compared with no field case. The relative gain of the PMT vs. the working voltage at different magnetic field intensities (0,0.5,1T) were also measured. An exponential dependence of the relative gain on the working voltage was observed for a wide range of the working voltage. Moreover,the factor k in the secondary electron emission ratio δ is measured to be less than the nominal value due to the special fine mesh structure of PMT's dynodes and it decreases with the increasing magnetic field intensities. It is the important reason that the gain of PMT decreases in case of strong magnetic field existence.
This paper mainly discusses what type of accelerating structure should be chosen for a novel compact electron linac (NCEL for short). After simulation of dynamics process in this linac with Parmela program,we get to the point that it is better on the whole,to choose constant impedance accelerating structure than constant gradient accelerating structure on the NCEL of 10MeV class.In this NCEL,the spent beam of a high power klystron amplifier is used for injecting into an accelerator section and the klystron works in self excited mode of operation. In this paper,the simulations of dynamics process,when the spent beam of a high power 5MW klystron is injected into a constant gradient structure and a constant impedance structure,are carried out. By comparing the output beam performances of these two kinds of structures,one can draw the conclusion that from overall consideration,it will be better to equip the NCEL with constant impedance structure than constant gradient structure,especially when the spent beam of much higher power klystron is used. At the same time the result of simulation indicates that it is unnecessary to use focusing coils around accelerating section,and thus the design will be further simplified for the NCEL.
A parallel self-consistent code SBBE to simulate the beam-beam effects in e+e- storage ring has been developed. It calculates the transverse kick in a collision by directly solving the Possion equation with an open boundary. Radiation damping effect and excitation random effect are included in arc transport. By using this code,the simulation of beam beam interaction on BEPC was made,and the simulated result was compared to the experiment result. The simulated luminosity agrees to the measured one qualitatively. The beam-beam limit was calculated in simulation and agreed well with the measured one.
Photoabsorption cross sections at the Al and Fe L2,3 edges on thin films have been measured at the Beijing Synchrotron Radiation Facility (BSRF) using monochromatic soft X-ray radiation. The measured Fe and Al cross sections are in good agreement with theoretical predictions for energy below the edge, while a poor agreement is observed near the edge region probably because the independent atom approximation is not suitable for photon energy near the absorption edge. Experimental data have been also compared with previous data available in the literature. This work demonstrates that cross section determinations of thin films of low Z atoms in the transmission mode are difficult but are feasible and can be substantially improved using synchrotron radiation.
Deoxyribonucleic acid (DNA) is an important biomacromolecule. It is a carrier of genetic information and a critical target for radiobiological effects. Numerous lesions have been identified in irradiated DNA. DNA double strand breaks (DSBs) are considered as the most important initial damage of all biological effects induced by ionizing radiation. In this experiment,DNA DSBs induced by heavy ions in the early period were investigated with atomic force microscopy (AFM). Choosing 7Li and 12C heavy ions with different LET values delivered by HI 13 tandem accelerator respectively,purified plasmid DNA samples in aqueous solution were irradiated at different doses. AFM was used for nanometer level structure analysis of DNA damage induced by these two kinds of heavy ions. Measurement of the DNA fragment lengths was accomplished with the Scion Image analyzed software. Change laws of three forms of DNA,supercoil,open circular and linear form as dose increased were obtained. Distributed function of DNA fragment length was also obtained,and fitted with Tsallis entropy statistical theory.
The uniformity of ICT image is impaired by beam hardening and the inconsistency of detector units responses. This paper analyzes the beam hardening and the nonlinearity of the detector's output. The correction factors are determined experimentally by the detector's responses with different absorption length. The artifacts in the CT image of a symmetrical aluminium cylinder have been eliminated after calibration.
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