## 2009 Vol. 33, No. 10

column

Display Method:          |

2009, 33(10): 819-825. doi: 10.1088/1674-1137/33/10/001
Abstract:

The Chinese second lunar satellite CE-2, which carries an X-ray spectrometer (XRS), will be launched at the end of 2010. In order to estimate the scientific results of XRS, we simulate the anticipated lunar X-ray spectra observed by XRS by using the expected mean solar X-ray flux in 2011. We also obtain the integration time and the spatial resolution required to achieve a certain significance level for the major lunar rock-forming elements in different solar activity conditions. It is expected that a spatial resolution of finer than 100 kilometers can be achieved for elements Mg, Al, Si, Ca, Ti, and Fe.

2009, 33(10): 826-833. doi: 10.1088/1674-1137/33/10/002
Abstract:

The perspective of the detectability of Galactic dark matter subhaloes on the Fermi satellite is investigated in this work. Under the assumptions that dark matter annihilation accounts for the GeV excess'' of the Galactic diffuse $\upgamma$-rays discovered by EGRET and the $\upgamma$-ray flux is dominated by the contribution from subhaloes of dark matter, we calculate the expected number of dark matter subhaloes that Fermi may detect. We show that Fermi may detect a few tens to several hundred subhaloes in a 1-year all-sky survey. Since EGRET observation is taken as a normalization, this prediction is independent of the particle physics property of dark matter. The uncertainties of the prediction are discussed in detail. We find that the major uncertainty comes from the mass function of subhaloes, i.e., whether the subhaloes are point like'' (high-mass rich) or diffuse like'' (low-mass rich). Other uncertainties like the background estimation and the observational errors will contribute a factor of 2—3.

2009, 33(10): 834-837. doi: 10.1088/1674-1137/33/10/003
Abstract:

Based on the Weinberg-Salam theory, the plasma neutrino energy loss rates of vector and axial-vector contributions are studied. A ratable factor of the rates from the axial-vector current relative to those of the total neutrino energy loss rates is accurately calculated. The results show that the ratable factor will reach a maximum of 0.95 or even more at relatively higher temperature and lower density (such as ρμe<107 g/cm3). Thus the rates of the axial-vector contribution cannot be neglected. On the other hand, the rates of the axial-vector contribution are on the order of ~0.01% of the total vector contribution, which is in good agreement with Itoh's at relatively high density (such as ρμe>107 g/cm3) and a temperature of T≤1011K.

2009, 33(10): 838-841. doi: 10.1088/1674-1137/33/10/004
Abstract:

Excited states of the positive-parity intruder band in 118Sn have been studied via the 116Cd(7Li, 1p4n) reaction at 7Li energy of 48 MeV using techniques of in-beam γ-ray spectroscopy. This intruder band has been observed up to 7187 keV with spin (16+). The structural evolution of this intruder band with increasing angular momentum has been discussed in terms of the aligned angular momentum and the ratio of the E-Gamma Over Spin (E-GOS) curve.

2009, 33(10): 842-847. doi: 10.1088/1674-1137/33/10/005
Abstract:

We study the effective masses of ρ-mesons for different charged states in asymmetric nuclear matter (ANM) using the Quantum Hadrodynamics II model. The closed form analytical results are presented for the effective masses of ρ-mesons. We have shown that the different charged ρ-mesons have mass splitting similar to various charged pions. The effect of the Dirac sea is also examined, and it is found that this effect is very important and leads to a reduction of the different charged ρ-meson masses in ANM.

2009, 33(10): 848-853. doi: 10.1088/1674-1137/33/10/006
Abstract:

The axially deformed relativistic mean field theory with the force NLSH has been performed in the blocked BCS approximation to investigate the properties and structure of N=Z nuclei from Z=20 to Z=48. Some ground state quantities such as binding energies, quadrupole deformations, one/two-nucleon separation energies, root-mean-square (rms) radii of charge and neutron, and shell gaps have been calculated. The results suggest that large deformations can be found in medium-heavy nuclei with N=Z=38—42. The charge and neutron rms radii increase rapidly beyond the magic number N=Z=28 until Z=42 with increasing nucleon number, which is similar to isotope shift, yet beyond Z=42, they decrease dramatically as the structure changes greatly from Z=42 to Z=43. The evolution of shell gaps with proton number Z can be clearly observed. Besides the appearance of possible new shell closures, some conventional shell closures have been found to disappear in some region. In addition, we found that the Coulomb interaction is not strong enough to break-down the shell structure of protons in the current region.

2009, 33(10): 854-859. doi: 10.1088/1674-1137/33/10/007
Abstract:

By studying the critical phenomena in continuum-percolation of discs, we find a new approach to locate the critical point, i.e. using the inflection point of P as an evaluation of the percolation threshold. The susceptibility, defined as the derivative of P, possesses a finite-size scaling property, where the scaling exponent is the reciprocal of ν, the critical exponent of the correlation length. A possible application of this approach to the study of the critical phenomena in relativistic heavy ion collisions is discussed. The critical point for deconfinement can be extracted by the inflection point of PQGP— the probability for the event with QGP formation. The finite-size scaling of its derivative can give the critical exponent ν, which is a rare case that can provide an experimental measure of a critical exponent in heavy ion collisions.

2009, 33(10): 860-865. doi: 10.1088/1674-1137/33/10/008
Abstract:

To perform a kinematically complete measurement of the dissociation reaction for neutron-rich nuclei, a multi-neutron correlation spectrometer is proposed at Peking University. A Monte Carlo simulation code based on GEANT4 is developed for a single scintillation bar which processes not only the energy deposition but also the light propagation in the scintillator and the light collection and conversion to signal at the end of the bar in a realistic way. The simulating method is described in detail in this paper, and the timing and position resolutions and detector efficiency are studied based on the simulation and compared with the experimental results. A new method of crosstalk rejection has been demonstrated to be important for the design of the whole spectrometer.

2009, 33(10): 866-869. doi: 10.1088/1674-1137/33/10/009
Abstract:

The total dose radiation response of pseudo-MOS transistors fabricated in hardened and unhardened FD (fully-depleted) SIMOX (Separation by Implanted Oxygen) SOI (Silicon-on-insulator) wafers is presented. At 1 Mrad(Si) radiation dose, the threshold voltage shift of the pseudo-MOS transistor is reduced from －115.5 to －1.9 V by the hardening procedure. The centroid location of the net positive charge trapped in BOX, the hole-trap density and the hole capture fraction of BOX are also shown. The results suggest that hardened FD SIMOX SOI wafers can perform well in a radiation environment.

2009, 33(10): 870-879. doi: 10.1088/1674-1137/33/10/010
Abstract:

A track fitting algorithm based on the Kalman filter method has been developed for BESⅢ of BEPCⅡ. The effects of multiple scattering and energy loss when the charged particles go through the detector, non-uniformity of magnetic field (NUMF) and wire sag, etc., have been carefully handled. This algorithm works well and the performance satisfies the physical requirements tested by the simulation data.

2009, 33(10): 880-886. doi: 10.1088/1674-1137/33/10/011
Abstract:

The BESⅢ detector has a high-resolution electromagnetic calorimeter which can be used for low momentum μ-π identification. Based on Monte Carlo simulations, μ-π separation was studied. A multilayer perceptron neural network making use of the defined variables was used to do the identification and a good μ-π separation result was obtained.

2009, 33(10): 887-891. doi: 10.1088/1674-1137/33/10/012
Abstract:

The present article describes a detailed neutron simulation study in the energy range 10－10 MeV to 1.0 GeV for two different RPC configurations. The simulation studies were taken by using the GEANT4 MC code. Aluminum was utilized on the GND and readout strips for the (a) Bakelite-based and (b) glass-based RPCs. For the former type of RPC setup the neutron sensitivity for the isotropic source was Sn=2.702×10－2 at En= 1.0 GeV, while for the latter type of RPC, the neutron sensitivity for the same source was evaluated as Sn= 4.049×10－2 at En= 1.0 GeV. These results were further compared with the previous RPC configuration in which copper was used for ground and pickup pads. Additionally Al was employed at (GND+strips) of the phosphate glass RPC setup and compared with the copper-based phosphate glass RPC. Good agreement with sensitivity values was obtained with the current and previous simulation results.

2009, 33(10): 892-896. doi: 10.1088/1674-1137/33/10/013
Abstract:

Helicon plasma sources are known as efficient generators of uniform and high density plasma. A helicon plasma source was developed for the investigation of plasma stripping and plasma lenses at the Institute of Modern Physics, CAS. In this paper, the characteristics of helicon plasma have been studied by using a Langmuir four-probe and a high plasma density up to 3.9×1013/cm3 has been achieved with the Nagoya type III antenna. In the experiment, several important phenomena were found: (1) for a given magnetic induction intensity, the plasma density became greater with the increase of RF power; (2) helicon mode appeared at RF power between 300 W and 400 W; (3) the plasma density gradually tended to saturation as the RF power increased to the higher power; (4) a higher plasma density can be obtained by a good match between the RF power and the magnetic field distribution. The key issue is how to optimize the matching between the RF power and the magnetic field. Moreover, some tests on the extraction of ion beams were performed, and preliminary results are given. The problems which existed in the helicon ion source will be discussed and the increase in beam density will be expected by extraction system optimum.

2009, 33(10): 897-900. doi: 10.1088/1674-1137/33/10/014
Abstract:

The beam trajectory in the first deflecting magnet of Rhodotron'' TT200 has been analyzed precisely by both optical and simulation methods. We found
discrepancies between these two methods at the order of (10－3) for the
slit distance and deflecting radius and at the order of (10－4) for the
magnetic flux density. The main goal of the paper is beam focusing, considering the angular and momentum dispersion of the particles for the magnet designed by ANSYS.

2009, 33(10): 901-904. doi: 10.1088/1674-1137/33/10/015
Abstract:

Based on the femtosecond accelerator device which was built at the Shanghai Institute of Applied Physics (SINAP), recently a modified far infrared Michelson interferometer has been developed to measure the length of electron bunches via the optical autocorrelation method. Compared with our former normal Michelson interferometer, we use a hollow retroreflector instead of a flat mirror as the reflective mirror. The experimental setup and results of the bunch length measurement will be described in this paper.

2009, 33(10): 905-913. doi: 10.1088/1674-1137/33/10/016
Abstract:

The betatron matching of a rotationally asymmetric beam in space charge
dominated low-energy beam transports (LEBTs) where solenoids are used for
the transverse matching has been studied. For better understanding, the
coupling elements of a beam matrix are interpreted in special forms that are
products of a term defined by the Larmor rotation angle and another by the
difference between the beam matrix elements in the two transverse planes.
The coupling form originally derived from the rotationally symmetric field
in solenoids still holds when taking into account the rotationally asymmetric space charge forces that are due to the unequal emittance in the two transverse planes. It is shown in this paper that when an LEBT mainly
comprising solenoids transports a beam having unequal emittance in the two
transverse planes and the linear space charge force is taken into account,
the initial Twiss parameters can be modified to obtain the minimum and equal
emittance at the LEBT exit. The TRACE3D calculations also prove the principle. However, when quadrupoles that are also rotationally asymmetric are involved in between solenoids, the coupling between the two transverse planes becomes more complicated and the emittance increase is usually unavoidable. A matching example using the CSNS (China Spallation Neutron Source) LEBT conditions is also presented.

2009, 33(10): 914-921. doi: 10.1088/1674-1137/33/10/017
Abstract:

The technique details for measuring radiation dose are expounded. The results
of gamma and neutron radiation levels are presented and the corresponding radiation shielding is discussed based on the simplified estimation. In addition, the photon radiation level move as background for future experiments is measured by a NaI(Tl) detector.

2009, 33(10): 922-925. doi: 10.1088/1674-1137/33/10/018
Abstract:

There are many methods based on linac for THz radiation production. As one of the options for the Beijing Advanced Light, an ERL test facility is proposed for THz radiation. In this test facility, there are 4 kinds of methods to produce THz radiation: coherent synchrotron radiation (CSR), synchrotron radiation (SR), low gain FEL oscillator, and high gain SASE FEL. In this paper, we study the characteristics of the 4 kinds of THz light sources.

2009, 33(10): 926-929. doi: 10.1088/1674-1137/33/10/019
Abstract:

Development activities of Radio Frequency Quadrupole (RFQ) accelerators in China are presented. A 1 MeV O+ RFQ and a 3.5 MeV ADS proton RFQ have been constructed. A novel separated function RFQ is under beam test, a 2 MeV D+ RFQ is under construction and a CSNS RFQ is going to be constructed. The RFQ dynamics and the simultaneous dual beam acceleration with positive and negative ions were investigated and related codes were developed. The applications of RFQ will be further promoted in China.

2009, 33(10): 930-934. doi: 10.1088/1674-1137/33/10/020
Abstract:

RF superconducting (SRF) cavities can work in continuous wave mode or long pulse mode. SRF technology has been developing rapidly since the end of the last century. RF superconducting technology widely used in particle accelerators around the world. As the key elements, research on superconducting cavities is carried out worldwide. Besides Europe, the United States and Japan, many countries have already started SRF projects, such as Canada, India, Korea, etc. Great improvements on SRF technology have been made in China in recent years. Progress in SRF cavities is introduced in this paper.