## 2007 Vol. 31, No. 7

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2007, 31(7): 607-611.
Abstract:
In the framework of the littlest Higgs(LH) model and the littlest Higgs model with T-parity(LHT), we investigate the single top production process eγ→νebt, and calculate the corrections of these two models to the cross section of this process. We find that in the reasonable parameter space, the correction terms for the tree-level Wtb couplings coming from the LHT model can generate significantly corrections to the cross section of this process, which might be detected in the future high energy linear e+e collider(ILC) experiments. However, the contributions of the new gauge boson W±H predicted by the LH model to this process are very small.
2007, 31(7): 612-616.
Abstract:
The performance of the Hard X-ray Modulation Telescope (HXMT) is significantly influenced by the collecting area. Based on the simulations of the background and the point spread function of the instrument, we propose a new collimator scheme in which the weight of the whole detectors can be decreased about 80kg. This is equal to the weight of 5 or more new detectors. We hope this new scheme will help to increase the number of detectors under the total loading mass limit, so that the collecting area will be larger and the performance of HXMT will be better.
2007, 31(7): 617-620.
Abstract:
We employ here a Relativistic Transport (ART) Model for Uranium $+$ Uranium collisions at Eb=0.52GeV/u. We study the impact parameter, rapidity and transverse momentum dependence of elliptic flow v2 for nucleons and pions in two extreme orientation UU collisions. It indicates that elliptic flow of nucleons and pions are always out-of plane as a result of squeeze-out effect. The maximal absolute value of elliptic flow, which is about 12%, appears in body-body certral UU collisons when the initial spatial anisotropy reach the maximum. In minibias events, the magnitudes of elliptic flow are similar for mid-rapidity nucleons in tip-tip and body-body UU collisions, but which is smaller for mid-rapidity pions in tip-tip. Nucleons and pions are produced primarily by Δ decay at low transverse momentum and by participator rescattering at high transverse momentum. Thus, elliptic flow in tip-tip and body-body are similar and have a visible drop in higher transverse momentum (Pt>0.3GeV/c) as a result of spectators rescatterings and reabsorbtionas.
2007, 31(7): 621-624.
Abstract:
The high spin states in neutron-deficient 134Ba nucleus have been studied by using heavy ion induced reaction 130Te(9Be,5n) and in-beam γ-ray spectroscopy carried out at China Institute of Atomic Energy. The level scheme has been updated with spin up to 20h. Most of levels and transitions reported in the previous publications have been confirmed. The levels in the ground state band was expanded to 10+ state, and many levels and transitions above the 10+ isomer have been identified. Based on the systematical analyzing, the 10+ isomer in 134Ba is a yrast trap of prolate deformation with γ≈－120° which is originated from two neutron configuration. Above the 10+ isomer level, the new levels show strong single-particle motion and complex structural characteristics. The obvious collective back-bending has been observed in the ground state band. The CSM calculations indicate that the back-bending of 134Ba is caused by alignment of a pair of h11/2 quasi-neutrons. The nuclear shape has obviously changed with rotational frequency increasing according to the TRS calculations, and the nucleus probably has an oblate deformation with γ≈－60° after the neutron alignment.
2007, 31(7): 625-628.
Abstract:
According to the regulation of growing and decay of artificial radioactive nuclide, a formula used to calculate the cross section of isomerous state with characteristic gamma-ray of ground state in a special case was deduced. And the cross sections of 128Te(n,2n)127mTe reaction induced by neutrons around 14MeV were measured and calculated by using the activation technique and the formula deduced above. The experimental results were (737±69) and (853±82)mb at the neutron energies of (14.1±0.2) and (14.6±0.3)MeV, respectively. The samples wrapped in cadmium foil were irradiated in order to avoid the effect of (n, γ) reaction induced by thermal neutron. The neutron energies in these measurements were determined by the method of cross-section ratios between 90Zr(n,2n) 89m+gZr and 93Nb(n,2n) 92mNb reactions, and the neutron fluencies were determined by using the monitor reaction 93Nb(n,2n) 92mNb.
2007, 31(7): 629-633.
Abstract:
In present paper several methods of evaluating discrepant data are introduced and compared each other briefly. The advantage and disadvantage of these methods(WM: weighted mean, LRSW: Limitation of relative statistical weights, MBAYS: Modified Bayesian Technique, NR: Normalized Residuals, and RA: Rajeval technique) are outlined. On the basis of these analysis and comparison, a new method i.e. Double-Mean method (DM) of evaluating discrepant data was proposed. The Double-Mean method takes into account the experimental uncertainties of different authors and all the available experimental information is fully considered. Thus the evaluated values of DM are less dependent on discrepant data and the uncertainties of the evaluated values are more reliable, i.e., the deviation between the evaluated results and the "true" values smaller than the other evaluation methods. The application of using the measured half-life and γ emission probability for 7Be is given as an example. The results of half-life and γ emission probability deduced from the present work are T1/2=(53.282±0.012)d and Pγ=(10.45±0.04)%, respectively.
2007, 31(7): 634-641.
Abstract:
The calculations of nucleus-nucleus potential are carried out in the framework of double folding model with M3Y-Reid and M3Y-Paris effective nucleon-nucleon (NN) interactions. The exchange part of the interaction, which is taken to be of finite range and the density dependence of NN interaction, is accounted for in the folding procedure. The results are used as the real part of the optical potential for heavy ion scattering. Besides, some general aspects of the folding model are reviewed and its theoretical processes are discussed. The calculated potentials with all kinds of NN interactions are compared. It is shown that the real parts of the optical potential for a large number of systems are obtained satisfactorily with our double folding model. Therefore, this work provides a promising way for a systematic and comprehensive double folding calculation of heavy ion interaction potential.
2007, 31(7): 642-646.
Abstract:
The decay scheme of 76Br is obtained by the 76Br (T1/2=16.2h)β+/EC approach. And the 1791.31keV level, which was identified firstly by Muller et al by the 76Se(p, p′) approach several years ago, is reconfirmed. However, Muller et al did not point out the spin and parity of this level, and which phonon multiplet it should be belong to. Now we consider the assertion that this level is assigned as a new candidate of the three-phonon multiplet in 76Se is reasonable. In addition, for researching deformation of 76Se which lies in the transitional region of strong deformed and spherical nuclei, we calculate the total Routhian surfaces (TRS) of positive-parity states by cranking shell model formalism.
2007, 31(7): 647-650.
Abstract:
A theoretical method for testing shell effect is proposed. In the framework of the relativistic mean-field theory with the consideration of the BCS approach, by calculating the fluctuation of the particle-number, we discover that particle number fluctuations are closely related with the nuclear shell structure. As a consequence, the traditional magic number N=28 disappears in the neutron-rich area near the drip-line.
2007, 31(7): 651-654.
Abstract:
The influences of the isospin dependent in-medium nucleon-nucleon cross section and the Momentum-Dependent Interaction(MDI) on the isotope scaling have been investigated within the Isospin dependent Quantum Molecular Dynamics Model(IQMD). The results show that both the isospin dependent in-medium nucleon-nucleon cross section and the momentum interaction reduce the isoscaling parameter α appreciably, which means they decrease the dependence of yield ratios of two systems on the isospin difference between two systems.
2007, 31(7): 655-659.
Abstract:
The passive beam delivery system in the superficially-placed tumor therapy terminal at Heavy Ion Research Facility in Lanzhou (HIRFL), which includes two orthogonal dipole magnets as scanning system, a motor-driven energy degrader as range-shifter, series of ridge filters as range modulator and a multileaf collimator, is introduced in detail. The capacities of its important components and the whole system have been verified experimentally. The tests of the ridge filter for extending Bragg peak and the range shifter for energy adjustment show both work well. To examine the passive beam delivery system, a beam shaping experiment were carried out, simulating a three-dimensional (3D) conformal irradiation to a tumor. The encouraging experimental result confirms that 3D layer-stacking conformal irradiation can be performed by means of the passive system. The validation of the beam delivery system establishes a substantial basis for upcoming clinical trial for superficially-placed tumors with heavy ions in the therapy terminal at HIRFL.
2007, 31(7): 660-663.
Abstract:
In the case that the mean value of Poisson distribution is a function of an unknown parameter to estimate, the commonly adopted maximum likelihood estimate of the parameter based on a single measurement is generally biased. With the aid of moment expressions, an unbiased estimator is proposed for the Poisson distribution.
2007, 31(7): 664-668.
Abstract:
Experimental study of the performance of triple-GEM and a multi-channel image was reported. The measured experimentally best energy resolution of 55Fe 5.9keV X-ray full energy photo electron peak is 20.2%, effective gain ≥104. Image was obtained by using 96 channels digital DAQ system which was composed of 96 8mm×8mm pads and 96 electronics channels.
2007, 31(7): 669-673.
Abstract:
A recoil separator Wien-filter which was developed for the Radioactive Ion Beam Line in Lanzhou (RIBLL) as an extension is described. It consists of 2 quadruple triplets and a standard Wien-filter. It was designed for study of the fusion-evaporation reactions. The overall design, background suppression, the transmission efficiency, the angular acceptance and the momentum acceptance have been described. All the performances fulfil the designed requirements. Based on the test results, with some modifications the investigations of the nuclei with Z≤110 and the drip-line nuclei in the medium-heavy mass region can be carried out with this facility.
2007, 31(7): 674-677.
Abstract:
The double pulsed electron beams' characteristics such as the movement position, the beams spot and the emittance were experimentally studied in the time-resolved mode. In the experiments, beam bugs were usedto detect the beam currents and the beam positions, and the Cerenkov radiation generated by the electron beams interacting with a quartz plate was used to get the information of the beams. The radiation was recorded by an 8 film streak camera. The experimental results indicate that the double pulsed relativistic beams emission from velvet has almost the same centroid movement, the same beam spots and the same emittances. The vacuum diode voltages are 1.75MV and the beam currents are about 1kA.
2007, 31(7): 678-682.
Abstract:
Numerical simulation of X-band metallic photonic band gap (PBG) accelerating structure based on a 3D electro-magnetic program is presented. The design of 11.42GHz traveling-wave accelerator has been successfully completed, including the RF-coupler design. At last, the electroforming technique is investigated here, with mechanical tolerances given by simulation.
2007, 31(7): 683-685.
Abstract:
The paper discusses the characteristic of signal transfers, reflection and phase shift of mcrowave system of Medical Standing Electron Linear Accelerator. The curve of the dose rate versus phase shift of microwave system for medical standing wave electron linear accelerator is given in the paper.
2007, 31(7): 686-701.
Abstract:
The theoretical explanations about the "ρπ" in charmonium decays are reviewed extensively, and the comparison of theoretical predications with experimental data is made whenever possible. Three methods to estimate the ratio of the branching fractions of J/ψ and ψ′ decays are also discussed. It is pointed out that in order to understand the ρπ puzzle, and the dynamics of charmonium decays, systematic studies should be made in theory, phenomenology and experiment aspects.