2005 Vol. 29, No. 10
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A 1:1 module of time of flight counter of BESⅢ is measured with the test beam of BEPC. Using 800MeV/c electron beam, the time resolution and attenuation length of light transition in plastic scintillators, BC408 and EJ200 packed with Al foil and Tyvek paper,are measured respectively. The optimum choice is EJ200 packed with Al foil. The measured time resolution of less than 90ps may satisfy the BESⅢ design requirement.
We study a top-Higgs production process e+e-→tcht0 in the topcolor assisted technicolor(TC2) model. The studies show that the production cross section of e+e-→tcht0 is at the order of magnitude 10fb in the reasonable parameters space of TC2 model. A few hundred events of top-Higgs can be produced each year at the high energy linear e+e- colliders(LC). The top-Higgs may be directly observed via this process.
The triton fragments produced in the reaction of 25MeV/u 6He on 9Be target were detected by a set of telescopes. Energy spectra at five angles and the angular differential cross sections for the direct breakup components were obtained. Serber model calculation was carried out which reproduces well the experimental distribution, in agreement with the assumption of the direct breakup mechanism. Fermi model calculation was also applied to estimate the contribution of the reaction phase space. Subtraction of this contribution from the experimental data indicates that the t+t configuration takes about 1/3 of the total probability in the initial state of 6He,whereas the configuration of 4He core plus valence neutrons takes another 2/3 of the total probability.
The total reaction cross sections for neutron-rich nucleus 8He at energy range from 25 to 40MeV/u on Si target have been measured and compared with the experimental data of R. E. Warner et al. The experiment data at high energy and low energy can be fitted well by Glauber model using two-term HO density distribution.
A dynamical study of the low energy nucleon-pion scattering phase shifts for $S$ and $P$ waves with isospin $I=1/2$ and $I=3/2$ is performed in the chiral $SU(3)$ quark model by solving a resonating group method equation. The model parameters are taken to be the values fitted by the energies of the baryon ground states and the kaon-nucleon elastic scattering phase shifts of different partial waves. Except for the resonant channels, the numerical results are in qualitative agreement with the experimental data.
The spin values of the superdeformed (SD) bands in A≈190 region have been assigned by comparing the fitting results of Bohr-Mottelson and Harris formulas.The assigned spin values in most of the SD bands are consistent in the both fitting results. For the superdeformed bands whose spin cannot be assigned consistently by the two formulas or the bands whose spin assignment doesn't accord with bandhead moments of inertial systematics, we assign their spin using moments of inertial systematics. By using our assigned spin values, the relation of parameters of Bohr-Mottelson formula has been examined. The results show that the relation deduced from three-parameter Harris formula is closer to the experiment than the relation deduced from ab formula.
Using the particle-number conserving (PNC) method for treating the cranked shell model,the microscopic mechanism of the variation with rotational frequency ω of the kinematics moments of inertia for the rare-earth deformed nuclei 178,179Hf is investigated. The 2-qp and 4-qp bands in 17872Hf and 3-qp bands in 17972Hf are analyzed and calculated.The observed ω variation of J(1) is reproduced satisfactorily in PNC calculations. Our analysis shows that the difference between the ω variations of J(1) for the high K multi-quasiparticle bands and for the ground state band is mainly due to the Pauli blocking effects of high j intruder orbitals near the Fermi surface.
Nucleon strange asymmetry is an important non-perturbative effect in the study of nucleon structure, but it has not been checked by experiments yet.For effectively measuring the nucleon strange asymmetry,we investigate the light quark fragmentation effect that may affect the measurement of the strange asymmetry.We suggest an inclusive measurement of charged and neutral charmed hadrons by using an emulsion target in the neutrino and antineutrino induced charged current deep inelastic scattering, in which the strange asymmetry effect and the light quark fragmentation effect can be separated.
The isospin-dependence of the relativistic microscopic optical potential is investigated in the Dirac Brueckner-Hartree-Fock approach. The isospin part of the microscopic optical potential is emphasized. A local density approximation is adopted for finite nuclei. Taking 208Pb as example,the difference between proton and neutron optical potentials is studied and compared with the phenomenological Lane Model potential.
The capture cross sections at stellar energies are very difficult to be measured directly. Hence,data are usually evaluated by means of indirect methods and extrapolations from the experimental data obtained at the possible lowest energies. In this work we have shown that the results obtained with the asymptotic normalization coefficient (ANC) method are nearly model independent. Therefore, the ANC approach of the transfer reactions provides a reliable way for the determination of the capture cross sections at stellar energies. By virtue of its reliability, we have calculated the capture cross sections of the 10Be (n,γ)11Be reaction by means of nuclear ANC method.11Be is a well-known neutron halo nucleus with two weak bound states. As a typical example, we have shown that the radiative cross sections for a nucleon captured into a halo state are obviously enhanced. The enormous enhancement of the capture cross section is just due to the large overlap of the incident neutron wave with the extended tail of the halo.
The special role of neutron-halo nucleus 19B on the momentum dissipation was investigated by using isospin dependent quantum molecular dynamics. In order to compare and protrude the special role of neutron-halo-nucleus 19B,the momentum dissipation induced by a same mass stable nucleus 19F was investigated under the same incident channel condition.It is found that the weak bound neutron-halo structure of 19B weakens the momentum dissipation process compared to those induced by stable nucleus 19F in the lower energy region. However the nuclear stopping of colliding system with the neutron-halo nucleus 19B decreases gradually with the increasing beam energy. For all of mass targets and impact parameters the neutron-halo nucleus 19B weakens the momentum dassipation process.
The water tank prototype with a dimension of 1m×1m×13m was constructed as a building block of the Cerenkov calorimeter for very long baseline neutrino oscillation experiments. The effective attenuation length of the water tank was measured to be (5.74±0.29)m, and the light collection probability as a function of the incident angle of the particle is studied. Results are compared with a Monte Carlo simulation based on GEANT4 package which incorporates detailed optical processes. A good agreement is achieved and the water tank is feasible for the construction of the Cerenkov calorimeter.
In this paper the influence of the space magnetic field on the performance of a superconducting niobium bulk cavity is introduced briefly. And an effective magnetic shielding method for superconducting cavity vertical test is presented. The initial permeabilities of eight different kinds of Fe-Si and Fe-Ni materials at liquid helium or liquid nitrogen temperature has been measured to compare with those at room temperature. The measurement data are given also. Based on it a double layers cylinder magnetic shield has been developed for the cryostat of 1.3GHz superconducting cavity.
The design of the isochronous magnet field and central region for 10MeV proton isochronous cyclotron has been studied. There is only one set of exciting coil, and the isochronous magnet field is mainly determined by the shape of magnet pole. The designed central region provides an enough large acceptance at the exit of PIG source for having a large beam current. The centering of the orbits is also permitted. The beam qualities are presented after 172 turn acceleration with the beam energy of 10MeV. The proton beam delivered by this cyclotron can be used in Positron Emission Tomography(PET) and so on.
4W1 magnet in BEPC for Synchrotron Radiation X-Ray beam lines consists of main resistance winding and auxiliary resistance winding which are respectively powered by two independent power supplies with high precision. These two power supplies called main power supply and auxiliary power supply are rebuilt with a new interface PSI (power supply interface).They are controlled by a PSC (power supply controller). This system is completed within one month after the control prototype for BEPCⅡ magnet power supplies with PSC/PSI has been finished. During the beginning of this system running, it is modified many times to meet its operation requirements. It has been running for about four months without big problems so that it ensures synchrotron radiation research on the two X-ray beam lines.This paper describes a new control system based on EPICS for 4W1 magnet power supplies.The requirements to 4W1 magnet ramp and its ramp programming are also discussed.
A novel resonator of quasi-periodic structure is introduced in the paper. On the accelerator CHP-01,its output power and frequency's dependences on system parameters are experimentally investigated. When voltage and current of repetitive diode are 790kV and 6.7kA, respectively, and its repetitive rate is 100Hz,the performance of 1.4GW microwave output power at 9.4GHz microwave frequency with 30ns pulse width and 26\% conversion efficiency are reached.
Within the framework of the pilot heavy-ion therapy facility at GSI equipping an active beam delivery system of advanced raster scanning technique, the investigation of actively conformal irradiation to moving tumors using heavy ions is underway. The influences of target motion on dose homogeneity and conformity degree were theoretically studied under the condition of the active raster-scanning beam delivery system.The relationship between the target motion with different patterns and the uniformities of doses delivered by the raster scanner to different iso-energy slices of the moving target were simulated with an experimentally measured beam spill. Several strategies improving the dose homogeneity in the moving target volume were derived from these simulation results. The simulations presented in this paper provide an effective means for evaluating the dose distribution for a moving target, and the results and implications of this theoretical work establish a substantial basis for feasibility experiments of the compensation for target motion with the active raster scanner at GSI.
Spatial(two-dimensional)distributions of inorganic elements such as chlorine,potassium, calcium,iron,copper,and zinc in the brain slices of Wistar rats were measured by synchrotron radiation X-ray fluorescence (SRXRF) analysis. Differences in two-dimensional distribution of these elements were observed. Chlorine, calcium, and zinc were primarily concentrated in hippocampus, while the potassium concentration was relatively higher in both cerebral cortex and hippocampus. However,the distribution of copper was comparatively ruleless in the three brain regions. The cluster analysis of the elemental results shows that the spatial distribution of chlorine was correlated well with the distribution of potassium.Since SRXRF is possible to obtain a pictorial representation of the elemental concentrations in tissue sections of brain, this nuclear method may be useful to evaluate the ionic changes in injured brain tissues in relation to histological observations.
A new method—axial scanning method (ASM)—is devised to find the position of the focal spot of polycapillary X-ray lens. The absolute errors of the results obtained by using ASM for output focal distance of polycapillary X-ray lens range from －120μm to 120μm. The energy dependence of the output focal distance of the polycapillary X-ray lens can be obtained by using the ASM over a broad energy range at the same time. The increase of the output focal distance of the lens with higher energies results from the decrease of the critical angle of total reflection with the increasing energies.
Using diffraction enhanced imaging (DEI), high contrast and high spatial resolution can be obtained on biological and medical samples, which are mainly composed by light atoms such as C, H, O, etc. Experiments show that the crystal reflectivity is the highest at the peak position of the rocking curve, determining shortest collection time for imaging.Therefore, using the DEI technique at the peak position of the rocking curve results in a reduced dose delivered to the sample. Although planar images of DEI exhibit high contrast and spatial resolution,the problem of the superposition of structural information contained in thick samples can not be easily resolved. As a consequence it is mandatory to combine DEI with a computerized tomography (CT) method. At the Beijing Synchrotron Radiation Facility (BSRF) we selected a fly as a test sample to carry out CT experiments for the first time using the peak-position images of DEI.Experimental data show a spatial resolution of the CT images of about tens of micrometers, which implies possible applications of the DEI technique to image processes on biological and medical samples expanding the fields of application of the technique such as early diagnosis of specific diseases on cells or tissues.
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