2008 Vol. 32, No. 8

Particle and field theory
Event generators at BESⅢ
PING Rong-Gang
2008, 32(8): 599-602. doi: 10.1088/1674-1137/32/8/001

We present a brief remark and introduction to event generators for tau-charm physics currently used at BESⅢ, including KKMC, BesEvtGen, Bhlumi, Bhwide, Babayaga and inclusive Monte-Carlo event generators. This paper provides basic information on event generators for BESⅢ users.

Study of semileptonic decays Bs→Ds1(2536)lν and Bs→Ds2(2573) lν in the CQM model
ZHAO Shu-Min, ZHANG Yin-Jie, YAN Yu-Li, LIU Li-Quan, WU Li-Ping
2008, 32(8): 603-607. doi: 10.1088/1674-1137/32/8/002

Based on the assumption that Ds1(2536) and Ds2(2573) belong to T doublet (1+,2+), we calculate the semileptonic decays of Bs to Ds1(2536) and Ds2(2573) in terms of the Constituent Quark Meson (CQM) model. For Bs→Ds1(2536)+lν and Bs→Ds2(2573)+lν, the order of magnitude of the obtained branching ratios is 10-3. Our numerical results of the semileptonic decays of Bs to Ds1(2536) and Ds2(2573) are large, which implies that two semileptonic decays should be seen
in future experiments.

Bounds on the magnetic moment of the τ-neutrino via the process e+e-→ννγ
C. Aydin, M. Bayar, N. Kilic
2008, 32(8): 608-611. doi: 10.1088/1674-1137/32/8/003

Using Breit-Wigner resonance relation, bounds on the magnetic moment of the
tau-neutrino are calculated through the reaction e+e→ννγ at the neutral boson pole in the framework of a superstring-inspired E6 model which has one extra low-energy neutral gauge boson and a LRSM.

particle and nuclear astrophysics and cosmology
Variation of the fine-structure constant from the de Sitter invariant special relativity
CHEN Shao-Xia, XIAO Neng-Chao, YAN Mu-Lin
2008, 32(8): 612-616. doi: 10.1088/1674-1137/32/8/004

We discuss the variation of the fine-structure constant, α. There are obvious discrepancies among the results of α-variation from recent Quasi-stellar observation experiments and from the Oklo uranium mine analysis. We use dS Sitter invariant Special Relativity (SRc,R) and Dirac large number hypothesis to discuss this puzzle, and present a possible solution to the disagreement. By means of the observational data and the discussions presented in this paper, we estimate the radius of the Universe in SRc,R which is about ~2√5×1011l.y.

Pair neutrino energy loss for nuclei 56Fe at the late stages of stellar evolution
LIU Jing-Jing, LUO Zhi-Quan
2008, 32(8): 617-619. doi: 10.1088/1674-1137/32/8/005

Based on the Weinberg-Salam theory, the pair neutrino energy loss rates for nuclei 56Fe are canvassed for the wide range of density and temperature. The results of ours (QLJ) are compared with those of Beaudet G, Petrosian V and Salpeter E. E's (QBPS), and it shows that the pair neutrino energy loss rates of QBPS are always larger than QLJ .The QBPS is 12.57%, 12.86%, 14.99%, 19.80% times higher than QLJ corresponding to the temperature T9=0.385, 1.0, 5.0, 10, respectively.

Nuclear and ion Physics
Track matching study from TPC to PHOS in ALICE
WAN Ren-Zhuo, XU Chun-Cheng, ZHOU Dai-Cui, YIN Zhong-Bao
2008, 32(8): 620-623. doi: 10.1088/1674-1137/32/8/006

We present a study for matching charged tracks reconstructed from the ALICE tracking detectors with the clusters measured in the photon spectrometer. Matching efficiency and contaminations due to wrong matches have been deduced for charged pions and muons. For electrons, the effect of the material in front of PHOS is discussed.

Steady state investigation on neutronics of a molten salt reactor considering the flow effect of fuel salt
ZHANG Da-Lin, QIU Sui-Zheng, LIU Chang-Liang, SU Guang-Hui
2008, 32(8): 624-628. doi: 10.1088/1674-1137/32/8/007

The Molten Salt Reactor (MSR), one of the `Generation IV' concepts, is a liquid-fuel reactor, which is different from the conventional reactors using solid fissile materials due to the flow effect of fuel salt. The study on its neutronics considering the fuel salt flow, which is the base of the thermal-hydraulic calculation and safety analysis, must be done. In this paper, the theoretical model on neutronics under steady condition for a single-liquid-fueled MSR is conducted and calculated by numerical method. The neutronics model consists of two group neutron diffusion equations for fast and thermal neutron fluxes, and balance equations for six-group delayed neutron precursors considering the flow effect of fuel salt. The spatial discretization of the above models is based on the finite volume method, and the discretization equations are computed by the source iteration method. The distributions of neutron fluxes and the distributions of the delayed neutron precursors in the core are obtained. The numerical calculated results show that, the fuel salt flow has little effect on the distribution of fast and thermal neutron fluxes and the effective multiplication factor; however, it affects the distribution of the delayed neutron precursors significantly, especially the long-lived one. In addition, it could be found that the delayed neutron precursors influence the neutronics slightly under the steady condition.

Role of t-channel meson exchanges in S-wave πN and KN scatterings
WU Feng-Quan, ZHANG Yin-Jie, ZOU Bing-Song
2008, 32(8): 629-633. doi: 10.1088/1674-1137/32/8/008

The low-energy S-wave πN and KN scatterings are studied by using the K-matrix approach within the meson exchange framework. The t-channel meson exchanges, especially ρ and σ exchanges, are found to play a very important role in these two processes. The t-channel ρ exchange determines the isospin structure of the scattering amplitudes, it gives attractive force in the low isospin state but repulsive force in the high isospin state. The t-channel σ exchange gives a very large contribution in these two processes, while it is negligible in meson-meson S-wave scatterings.

α decay energies and half-lives from a macroscopic-microscopic model
PENG Jin-Song, LI Lu-Lu, ZHOU Shan-Gui, ZHAO En-Guang
2008, 32(8): 634-638. doi: 10.1088/1674-1137/32/8/009

α decay energies of 323 heavy nuclei with Z≥82 are evaluated with a macroscopic-microscopic model. In this model, the macroscopic part is treated by the continuous medium model and the microscopic part consists of shell and pairing corrections based on the Nilsson potential. α decay half-lives are calculated by Viola-Seaborg formula. The results of α decay energies and half-lives are compared with experimental values and satisfactory agreement is found. The recoiling effect of the daughter nucleus on α decay half-life is also discussed.

Analysis of charged hadron multiplicity distributions at RHIC
XIONG Wei, FENG Sheng-Qin
2008, 32(8): 639-644. doi: 10.1088/1674-1137/32/8/010

It is demonstrated that with Heinz's collective flow model charged particle distributions at AGS and lower SPS energies (less than 20 GeV/n) , can successfully be analyzed, but that the model fails for the RHIC data. Heinz's model calculation underestimates the tails of the charged particle distributions from RHIC, the discrepancy becoming bigger as the energy increases. To study the multiplicity distributions at RHIC we develop the so-called "Thermalization Component Model'', which is based on Heinz's collective flow model. It is realized that the limitation of phase space of collective flow can be reflected in that of the thermalization region. By comparing the contributions of particle production from the thermalization regions at different energies and different centralities, we can deepen our understanding of the features of collective motion at RHIC.

Detection Technology and Methods
Total dose radiation effects on SOI NMOS transistors with different layouts
TIAN Hao, ZHANG Zheng-Xuan, HE Wei, YU Wen-Jie, WANG Ru, CHEN Ming
2008, 32(8): 645-648. doi: 10.1088/1674-1137/32/8/011

Partially-depleted Silicon-On-Insulator Negative Channel Metal Oxide Semiconductor (SOI NMOS) transistors with different layouts are fabricated on radiation hard Separation by IMplanted OXygen (SIMOX) substrate and tested using 10keV X-ray radiation sources. The radiation performance is characterized by transistor threshold voltage shift and transistor leakage currents as a function of the total dose up to 2.0×106 rad(Si). The results show that the total dose radiation effects on NMOS devices are very sensitive to their layout structures.

Design and implementation of the detector control system for the BESⅢ drift chamber cosmic ray test
CHEN Xi-Hui, XIE Xiao-Xi, LI Xiao-Nan, GAO Cui-Shan, ZHANG Yin-Hong, NIE Zhen-Dong, MIN Jian, XIE Yi-GANG
2008, 32(8): 649-652. doi: 10.1088/1674-1137/32/8/012

After the construction of the BESⅢ drift chamber, a long period of cosmic rays test is necessary to verify its performance. This also provides a good opportunity to integrate the detector readout electronics and Detector Control System (DCS) into a unified working system. The goal of the DCS is to guarantee reliable physics data quality and the safe operation of the detector. It monitors and controls the HV, gas, VME crates and the nvironmental variables. The upper-level system is mainly developed from LabVIEW and the lower-level system mainly uses MCU and PLC technology. The system is designed to be highly flexible and scalable so that it can be applied to other detectors with little or no change. In the immediate future, it will be integrated into the entire BESⅢ Slow Control System.

Nitrogen dilution effect for small angle GDH experiment in JLab Hall-A
YE Yun-Xiu, YAN Xin-Hu, CHENG He-Ping, JIAO Zheng, HE Ju, LIU Ren-Chen
2008, 32(8): 653-656. doi: 013

In the GDH sum rule measurement in JLab Hall-A, to obtain the cross section of electron scattering on polarized 3He and its asymmetry in different helicity states, the dilution effect from unpolarized nitrogen mixed in the polarized 3He target were calculated at different kinematic settings.

RF gun for an intense THz radiation source
GU Qiang, ZHAO Zhen-Tang, TONG De-Chun, CHEN Li-Fang, XU Xiu-Min
2008, 32(8): 657-660. doi: 10.1088/1674-1137/32/8/014

A new facility is under construction at the Shanghai Institute of Applied Physics, to generate femto-second electron bunches and intense coherent THz radiation pulses. A thermionic RF-gun is used to be the electron source of the linac, which is 1.6 cell, π2, side coupled in design. In the following of this paper, the design, manufacture and beam operation of this gun are presented.

New chromaticity compensation approach and dynamic aperture increase in the SSRF storage ring
TIAN Shun-Qiang, HOU Jie, CHEN Guang-Ling, LIU Gui-Min
2008, 32(8): 661-664. doi: 10.1088/1674-1137/32/8/015

Strong chromatic sextupoles used to compensate natural chromaticities in the third generation light source storage ring usually reduce dynamic aperture drastically. Many optimization methods can be used to find solutions that provide large dynamic apertures. This paper discusses a new optimization approach of sextupole strengths with step-by-step procedure, which is applied in the SSRF storage ring, and a better solution is obtained. Investigating driving terms generated by the sextupoles in every step can analyze their convergences and guide the weight setting among different terms in object function of the single resonance approach based on the perturbation theory.

Impact on the magnetic compressor due to CSR
LIU Chu-Yu, WANG Fang, WANG Er-Dong, QUAN Sheng-Wen, HAO Jian-Kui, LU Xiang-Yang, ZHANG Bao-Cheng, ZHAO Kui
2008, 32(8): 665-667. doi: 10.1088/1674-1137/32/8/016

When an electron bunch is compressed in a chicane compressor, the CSR (coherent synchrotron radiation) will induce energy redistribution along the bunch. Such energy redistribution will affect the longitudinal emittance as a direct consequence. It will also excite betatron oscillation due to the chromatic transfer functions, and hence a transverse emittance change. So, it is indispensable for us to find a way to alleviate the CSR-caused emittance dilution and the bad result of chicane compressor in PKU-FEL.

Design of magnet and control of the beam emittance for Penning H ion source
2008, 32(8): 668-672. doi: 10.1088/1674-1137/32/8/017

The design requirement and principle of the deflection magnet for Magnetron and Penning H ion source are discussed. It is proved that there exists a maximum emittance for the beam that may be transformed by the magnet into a state with equal Twiss parameters of αry and βry, which is the requisite condition to get a minimum emittance at the entrance of RFQ after transporting by a LEBT with solenoids. For this maximum emittance, the corresponding magnetic field gradient index is 1.

Synchrotron radiation,applications of nuclear techniquees,etc
Transmission measurement of photo-absorption cross section of aluminum in soft X-ray region of 50 to 250eV
CHEN Kai, CUI Ming-Qi, ZHENG Lei
2008, 32(8): 673-676. doi: 10.1088/1674-1137/32/8/018

The photo-absorption cross section of aluminum was obtained from the ratio of transmission of aluminum thin-films with different area densities from 50 to 250eV with synchrotron radiation monochromatic beam. Two samples with different area densities were used to minimize the uncertainty caused by the sample surface oxidation and systematic factors of the X-ray source, beamline, and detector. The experimental results are in good agreement with the published data and FEFF program calculations in general.

Transmutation of nuclear wastes using photonuclear reactions triggered by Compton backscattering photons at the Shanghai laser electron gamma source
CHEN Jin-Gen, XU Wang, WANG Hong-Wei, GUO Wei, MA Yu-Gang, CAI Xiang-Zhou, LU Guang-Cheng, XU Yi, PAN Qiang-Yan, YUAN Ren-Yong, XU Jia-Qiang, YAN Zhe, FAN Gong-Tao, SHEN Wen-Qing
2008, 32(8): 677-680. doi: 10.1088/1674-1137/32/8/019

Based on the facility of the Shanghai Laser Electron Gamma Source (SLEGS), the transmutation for nuclear wastes such as 137Cs and 129I is investigated. It is found that nuclear waste can be transmuted efficiently via photonuclear reaction triggered by gamma photons generated from Compton backscattering between CO2 laser photons and 3.5 GeV electrons. The nuclear activities of 137Cs and 129I are evaluated and compared with the results of transmutation triggered by bremsstrahlung gamma photons driven by ultra intense laser. Due to the better character of gamma photon spectrum as well as the high brightness of gamma photons, the transmutation rate of Compton backscattering method is much higher than that of the bremsstrahlung method.