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2015 Vol. 32, No. 2

Nuclear Dynamics at the Particle Threshold
Nadia Tsoneva, Horst Lenske
2015, 32(2): 129-136. doi: 10.11804/NuclPhysRev.32.02.129
Recently, new low-energy modes of excitation called pygmy resonances have been observed.Their distinct feature is the close connection to nuclear skin oscillations. A successful description of the pygmy resonances could be achieved in a microscopic theoretical approach which incorporates the density functional theory and QRPA formalism extended with multi-phonon degrees of freedom. The latter is found of crucial importance for the understanding of the fine structure of nuclear electric and magnetic excitations at low energies. Corresponding microscopic multi-phonon response functions are implemented in the studies of s-process of nucleosynthesis.
Production of Exotic Nuclei in Low-Energy Multi-Nucleon Transfer Reactions
V.I. Zagrebaev, Walter Greiner
2015, 32(2): 137-145. doi: 10.11804/NuclPhysRev.32.02.137
Abstract(840) PDF (708KB)(1237)
Multinucleon transfer processes in low-energy heavy ion collisions open a new field of research in nuclear physics, namely, production and studying properties of heavy neutron rich nuclei. This not-yet-explored area of the nuclear map is extremely important for understanding the astrophysical nucleosynthesis and the origin of heavy elements. Beams of very heavy U-like ions are needed to produce new long-living isotopes of transfermium and superheavy elements located very close to the island of stability.The calculated cross sections are high enough to perform the experiments at available accelerators.Beams of medium-mass ions (such as 136Xe, 192Os, 198Pt) can be used for the production of neutron rich nuclei located along the neutron closed shell N = 126 (the last waiting point) having the largest impact on the astrophysical r-process. The Low-energy multinucleon transfer reactions is a very efficient tool also for the production and spectroscopic study of light exotic nuclei. The corresponding cross sections are 2 or 3 orders of magnitude larger as compared with high energy fragmentation reactions.
Mean-field Effects on Particle and Antiparticle Elliptic Flows in the Beam-energy Scan Program at RHIC
XU Jun, KO Cheming, LI Feng, SONG Taesoo, LIU He
2015, 32(2): 146-153. doi: 10.11804/NuclPhysRev.32.02.146
Abstract(1036) PDF (410KB)(473)
The elliptic flow splitting between particles and their antiparticles has recently been observed by the STAR Collaboration in the beam-energy scan program at the Relativistic Heavy Ion Collider. In studies based on transport models, we have found that this splitting can be explained by the different mean-field potentials acting on particles and their antiparticles in the produced baryon-rich matter. In particular, we have shown that the experimentally measured relative elliptic flow difference can help constrain the vector coupling constant in the Nambu-Jona-Lasinio model used in describing the partonic stage of heavy-ion collisions. This information is useful for locating the critical point in the QCD phase diagram and thus understanding the phase structure of QCD.
Constraining the Symmetry Energy Using Elliptic Flow and Yield Ratios of Light Particles
WANG Yongjia, GUO Chenchen, LI Qingfeng, SUN Yuliang
2015, 32(2): 154-160. doi: 10.11804/NuclPhysRev.32.02.154
Based on the newly updated version of the Ultra-relativistic quantum molecular dynamics (UrQMD) model, the transverse-momentum dependent elliptic flow ratio of free neutrons vs hydrogen isotopes and the yield ratio of 3H vs 3He clusters emitted from 197Au+197Au collisions at the incident energy 400 MeV/nucleon are studied. It is found that the elliptic flow ratio vn 2 /vH 2 is sensitive to the symmetry energy at supra-saturation densities, while the yield ratio 3H/3He is sensitive to the nuclear symmetry energy at sub-saturation densities. By comparing the data from FOPI/LAND and FOPI Collaborations with model calculations using various Skyrme interactions (all exhibiting similar values of isoscalar incompressibility but very different density dependences of the symmetry energy), we find that results using Skyrme interactions which parameterize a moderately soft to linear symmetry energy can reproduce both data quite well.
Constraint on Properties of Rapidly Rotating Neutron Stars from Nuclear Symmetry Energy Slope
WEN Dehua, JING Zhenzhen
2015, 32(2): 161-169. doi: 10.11804/NuclPhysRev.32.02.161
During the past decade, theoretical researches and terrestrial nuclear laboratory experiments have made impressive progresses on the researches of symmetry energy of the asymmetric nuclear matters, which is very important in understanding the equation of states and the structures of neutron stars. In this work, by making use of a conservative symmetry energy slope (SES) range (25 MeVare investigated. The constraint properties include the mass-radius relations, the moments of inertia, the redshift, the deformations of the rapid rotating stars, etc. According to the conservative SES range, it is shown that the radius of a canonical neutron star (with M = 1.4M⊙) can be constrained in a region of 10.28 s 13.43 km, which is consistent with one of the latest constraints on the radius of neutron star in observations. It is also shown that if a sub-millisecond pulsar with a lighter stellar mass is observed in the future, then a softer SES of the asymmetric nuclear matters is preferred. The universal property of the angular momentum provides a way to obtain the upper limit of the moment of inertia of a rapid rotating neutron star with observed mass. Moreover, the results also can provide a constraint on the lower mass limit (>1.5M⊙) of pulsar in low-mass X-ray binary EXO0748-676 if the observed redshift of this star is from the polar direction.
Freeze-out Concept in Antisymmetrized Molecular Dynamics
LIN Weiping, LIU Xingquan, HUANG Meirong, ZHANG Suyalatu, CHEN Zhiqiang, WANG Jiansong, HAN Rui, LIU Jianli, REN Peipei, SHI Fudong, Roy Wada
2015, 32(2): 170-174. doi: 10.11804/NuclPhysRev.32.02.170
Abstract(1030) PDF (368KB)(534)
As a part of statistical freeze-out study in antisymmetrized molecular dynamics (AMD), an analysis of 112Sn+112Sn at 50 MeV/nucleon is presented. Using the self-consistent method combined with the Modified Fisher model, the fragmenting source density, ρ/ρ0=0.69±0.03, temperature, T =(6.1±0.2)MeV, are extracted. By comparing the maximum density in the system during the time evolution of AMD calculation, a significantly lower density is found for the fragmenting source density. The extracted
fragmenting source density and temperature are very similar to those for 40Ca + 40Ca at 35 MeV/nucleon and 64Zn + 112Sn at 40 MeV/nucleon. These indicate that there is a common statistical freeze-out volume at the time of the formation of intermediate mass fragments (IMFs) in AMD transport model.
Angular Anisotropy of the Fission Fragments in the Dinuclear System Model
T. M. Shneidman, A. V. Andreev, C. Massimi, M. T. Pigni, G. Vannini, A. Ventura, S. G. Zhou
2015, 32(2): 175-179. doi: 10.11804/NuclPhysRev.32.02.175
A theoretical evaluation of the collective excitation spectra of nucleus at large deformations is possible within the framework of the dinuclear system (DNS) model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two-cluster configurations in a dynamical way, permitting exchange of nucleons between clusters. In this work the method of calculation of the potential energy and the collective spectrum of fissioning nucleus at scission point is presented. Combining the DNS model calculations and the statistical model of fission we calculate the angular distribution of fission fragments for the neutron–induced fission of 239Pu.
Angular Momentum Effect on Probing Nuclear Dissipation with Fission Cross Section
YE Wei, TIAN Jian
2015, 32(2): 180-183. doi: 10.11804/NuclPhysRev.32.02.180
Using the Langevin model, we study the effect of angular momentum on the drop of fission cross sections caused by friction over its standard statistical-model value, σdrop
f, as a function of presaddle friction strength β. It is found that friction effects on σdrop
f are substantially enhanced at low spin. In addition, by investigating the evolution of σdrop f with β for 195Bi, 201Bi and 207Bi nuclei, we find that friction effects become greater with increasing the neutron-to-proton ratio (N/Z) of Bi nucleus. These results suggest that on the experimental side, to precisely probe presaddle dissipation by measuring fission excitation functions, it is best to yield excited nuclear systems with a small spin and a large N/Z.
Dynamically Generated Resonances in the Partial Wave Analysis of the Vector Meson- octet Baryon Interaction
SUN Baoxi.DONG Fangyong, LU Xiaofu
2015, 32(2): 184-190. doi: 10.11804/NuclPhysRev.32.02.184
Abstract(1056) PDF (198KB)(444)
The interaction kernels between vector mesons and octet baryons are calculated explicitly with a summation of t-, s-, u- channel diagrams and a contact term originating from the tensor interaction.Many resonances are generated dynamically in different channels of strangeness zero by solving the coupled-channel Lippman-Schwinger equations with the method of partial wave analysis, and their total angular momenta are determined. The spin partners N(1650)1/2− and N(1700)3/2−, N(1895)1/2− and N(1875)3/2−, and the state N(2120)3/2− are all produced respectively in the isospin I =1/2 sector. In the isospin I =3/2 sector, the spin partners Δ(1620)1/2− and Δ(1700)3/2− are also associated with the pole in the complex energy plane. According to the calculation results, a JP =1/2− state around 2 000 MeV is predicted as the spin partner of N(2120)3/2−.
High Intensity Beam Transport Study with TOPOPIC in FODO Structure
LI Chao, QI Xin, ZHANG Zhilei, HE Yuan, YANG Lei
2015, 32(2): 191-195. doi: 10.11804/NuclPhysRev.32.02.191
Abstract(1124) PDF (508KB)(457)
The Particle in cell (PIC) method is one of the key techniques in the research of charged particles in accelerators. Based on the PIC method, a new beam simulation code for high intensity beam named TOPOPIC (Trace of particle orbit with PIC method) has been developed. With the code TOPOPIC,the beam behavior during passing through the periodic quadrupole (FODO) structure has been studied. The results show that the nonlinear space charge affects the single particle behavior and beam envelope a lot. At last, the PIC code BEAMPATH is used for benchmark, the results given by TOPOPIC and BEAMPATH show good agreements,which means the code TOPOPIC is reliable.
Test of LLRF Control System on Superconducting Cavity
ZHU Zhenglong, WANG Xianwu, LI Chunlong, CHANG Wei, ZHANG Shenghu, ZHANG Junhui, ZHANG Ruifeng, WEN Lianghua, GAO Zheng, CHEN Qi, YUE Weiming, SONG Yukun
2015, 32(2): 196-201. doi: 10.11804/NuclPhysRev.32.02.196
Abstract(1077) PDF (660KB)(484)
The first generation Low-Level radio frequency(LLRF) control systemfor China ADS injector Ⅱis developed by IMP, CAS(Institute of Modern Physics, Chinese Academy of Sciences). This system is composed by superconducting cavity amplitude stability controller, phase stability controller and the cavity resonance frequency controller; the operation frequency is 162.5 MHz. This is an all-digital closed-loop feedback control
system which based on the IQ quadrature sampling demodulation technique. The performance of the system has been tested on the superconducting cavity, which is running in the temperature range of liquid helium and the Epk=25.1 MV/m (the peak electricon the surface of the superconducting cavity). The amplitude stability is less
than .4 ‰ and the phase stability is less than 0.3°. Superconducting cavity bandwidth is about 230 Hz. From the spectrum, the phase noise suppression can reach 70 dBm.
Nuclear Technology
Design of a Low Noise, Wide Dynamic Range and Small Dimension Front-end Circuit
SUN Wen, QIAN Yi, SU Hong, DONG Chengfu, ZHAO Xingwen, WANG Xiaohui, LI Xiaogang, MA Xiaoli, YANG Haibo
2015, 32(2): 202-211. doi: 10.11804/NuclPhysRev.32.02.202
A small dimension front-end circuit with low noise and wide output dynamic range is introduced in this paper. The front-end circuit is made up of a charge sensitive preamplifier, a shaping circuit and a single channel pulse height analyzer. The equivalent input noise is under 1.5 keV. The output integral nonlinearity is less than 0.11% within the dynamic range of 011 V. And the circuit can be suitable for different conditions by different modules. The resolution was about 0.12% with the charge sensitive preamplifier and the main amplifier. The energy resolution of 0.82% was achieved for 5.157 MeV -rays from a 239Pu source with the charge sensitive preamplifier, the main amplifier and anion-injection silicon detector designed by the Institute of Modern Physics(IMP). An energy resolution of 7.9% was achieved for 1.332 MeV rays from a stationary 60Co source with the main amplifier, the single channel pulse height analyzer and a CsI scintillator detector designed by the IMP. The front-end circuit has the features of wide output dynamic range, simple structure, high level of integration,small dimensions, low noise, fast rise time of the output pulse and excellent stability. The front-end circuit can be applied to signal processing of semiconductor detectors, photomultiplier tubes and electrons multiplier. And the front-end circuit had been applied to a prototype of the portable rapid measuring instrument designed by IMP for measuring Uranium, Thorium and Potassium in the salt lake brine with good
test result.
Neutron Shielding Design for Experiment Research of (n,γ) Reaction
HUANG Xing, HE Guozhu, CHENG Pinjing, ZHANG Qiwei, ZHOU Zuying
2015, 32(2): 208-211. doi: 10.11804/NuclPhysRev.32.02.208
Neutron capture cross section can be measured by Gamma-ray Total Absorption Facility (GTAF) with high precision. To reduce the background of experiments, the neutron source must be collimated and shielded, and the neutrons scattered from the sample must be absorbed to minimise interference after they go into the detector. The shield, collimator and absorber were simulated and designed with MCNP code. Boron-ontaining polyethylene with 3% BC4 and lead are used as the materials for the neutron collimator and shield. The diameter of the collimating aperture is 13 mm, and the length of the collimator is 500 mm. After being collimated, the diameter of neutron beam plateau at the sample position is 21 mm. The neutron absorber is made of polyethylene and BC4, and the thickness of polyethylene shell and BC4 shell are 60 and 10 mm, respectively. The simulated result shows that neutrons scattered from the sample can decay 93.7% through the neutron absorber.
Simulation Investigations on the Absorbed Dose in Lung Tissue from Inhaled Tritiated Particles
SUN Ruofan, MAO Li, WU Qiqi, AN Zhu
2015, 32(2): 212-217. doi: 10.11804/NuclPhysRev.32.02.212
Some tritium relevant nuclear facilities, such as Tokamak, can produce tritiated particles. There is the possibility for the staffs to inhale the tritiated particles by accident in the process of maintenance or decommission of these facilities. Tritium decays to 3He, during which the beta electron and the internal bremsstrahlung are released. Meanwhile, the released electrons will interact with the surrounding atoms, and the external bremsstrahlung will be generated. All the electrons, internal bremsstrahlung and external bremsstrahlung will deposit the radiation energies to lung tissues and generate the radiation damage. In this paper we studied the radiation doses by inhaled tritiated particles in lung tissues by Monte Carlo code PENELOPE, in particular, internal bremsstrahlung contribution was included. Our results demonstrated that (1) the dose caused by electron radiation is far higher than those of external and internal bremsstrahlung, which however shall not be negligible due to their long-distance effects; (2) the dose caused by electron radiation decreases as the particle size and metal atomic number Z increase; (3) the dose caused by external bremsstrahlung decreases as the particle size increases, but increases as the metal Z increases; (4) the dose caused by internal bremsstrahlung decreases as the particle size and metal Z increase.
Analysis of Digital Waveform Methods with DRS4 Evaluation Board
CHEN Ze, HU Zhengguo, CHEN Jinda, ZHANG Xiuling, GUO Zhongyan, XIAO Guoqing, SUN Zhiyu, HUANG Wenxue, WANG Jiansong
2015, 32(2): 218-223. doi: 10.11804/NuclPhysRev.32.02.218
Various digital methods were examined for determining the relative arrival times of pulses from 20 mm x 5 mm LaBr3 scintillators. In this study, pulses from the photomultiplier tubes (PMTs) were digitized by DRS4 evaluation board, a switched capacitor array (SCA) produced by the Paul Scherrer Institute (PSI). The high bandwidth, low power consumption and short readout time make DRS4 attractive for many experiments, replacing traditional ADCs and TDCs. The sampling signals were post processed with multiple techniques. These techniques include: (1) constant-raction discrimination (CFD), (2) pulse-shape fitting, (3) mean PMT pulse model and (4) median filtered zero crossing method.The implemented CFD in the digital regimes did not improve the resolution of using analog equipmentwith average time resolution. The pulse-shape fitting yielded as good resolution as digital CFD, however,is much more time consuming. The median filtered method were easy to implement, and had a resolution on the order of sampling time. Average timing resolutions of 195.4 ps were obtained with mean PMT pulse model, which is better than the analog constant-fraction-zero-crossing with average resolution of 254.7 ps.
MC Calculation of Neutron Response for an Extended Range Multisphere Neutron Spectrometer
YUAN Jiao, SU Youwu, LI Wuyuan, XU Junkui, PANG Chengguo, YAN Weiwei, LI Zongqiang, MAO Wang, ZUO Wei
2015, 32(2): 224-229. doi: 10.11804/NuclPhysRev.32.02.224
The responses of an extended range Multisphere Neutron Spectrometer as function of neutron energy were calculated by Monte Carlo code,FLUKA. The results show that peak value of the response curve shift to the right with the increasing of polyethylene thickness, but decreases in the high energy region. For neutron with energy >20 MeV, the response of polyethylene moderator will be decreased to be a very low level no matter what size it is. For neutron energies below 1 MeV, the response curve of moderator with auxiliary materials behave like the one of polyethylene moderator, but above 20 MeV the responses increase signi cantly due to increasing (n, xn) cross-sections of auxiliary materials. Based on the present discussion, the size of an extended range multisphere neutron spectrometer can be determined.
Cross Discipline
Research on the Radiosensitizing Effect of Gold Nanoparticles
LIU Xi, LIU Yan, CHEN Weiqiang, LI Qiang
2015, 32(2): 230-235. doi: 10.11804/NuclPhysRev.32.02.230
This paper describes the methods and results of the previous experiments, the experimental phenomena of the cell and animal tests and the relative mechanisms on the radiosensitizing effect of GNPs. Together with our experiments, the radiosensitizing effects of 15 nm citrate-capped GNPs and related mechanisms are analyzed and compared, finding that Hela cell killing of GNPs increase along with their concentration after exposure to high- and low-LET radiation such as carbon ions and X-rays. In addition, the percentages of dose reduction of the X-rays and RBE increment of the carbon ions reached their maximums 65.3% and 43.6%, respectively,at 50% survival level when Hela cells were pre-treated with 7.5 g/mL GNPs. Moreover, Hela cells showed no cell-cycle synchronization after 24 and 48 h exposure to GNPs.
Effect of Endoplasmic Reticulum Stress on the Response of HeLa Cells to Carbon Ion Radiation
XIA Jiefang, WANG Zhuanzi, WEI Wei, DANG Bingrong, LI Wenjian
2015, 32(2): 236-241. doi: 10.11804/NuclPhysRev.32.02.236
To investigate the effect of endoplasmic reticulum stress on HeLa cells to 12C6+ ion irradiation,HeLa cells were pretreated with 2.5 mmol/L dithiothreitol and irradiated by 12C6+ ions with different doses.The results showed that, compared with IR alone, dithiothreitol combined with carbon ion irradiation caused HeLa cell survival decreased, and the apoptosis increased. Moreover, dithiothreitol and carbon ion radiation combination treatment led to a significant increase of G2/M phase, and autophagy was activated obviously in combination treatment group. The results imply that continuous endoplasmic reticulum stress can change the response of HeLa cells to 12C6+ irradiation, and dithiothreitol may affect HeLa cells through the autophagy cell death pathway.
Fabrication of TiO2 Nano lms by Ti+ Ion Implantation and Subsequent Thermal Annealing
ZHOU Xiaodong
2015, 32(2): 242-248. doi: 10.11804/NuclPhysRev.32.02.242
TiO2 nanofilms on the surface of fused silica have been fabricated by Ti+ ion implantation and subsequent thermal annealing in oxygen ambience. The silica glasses were implanted by Ti+ ions at 20 kV with fluences of 1.5 and 3x1017 ions/cm2 using a metal vapor vacuum arc (MEVVA) ion source implanter. The optical absorption spectroscopy, Raman scattering spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) measurements were done to figure out formation mechanism of the TiO2 nanofilms. The formation of TiO2 nanofilms resulted from outdiffusion of the implanted Ti ions to the substrate surface, where they were oxidized intoTiO2. The formation,grain size and the crystallographic phase of TiO2 are annealing temperature dependent, and TiO2 nanofilm thickness can be well tailored by controlling the implantation fluence and annealing time. Results show that the TiO2 nanofilms fabricated by this novel method have great potential in applications such as photocatalytic,antibacterial and self-cleaning glass.
Radiation Damage Characterization of InGaAsP Laser Diodes for Space Laser Communication
GAO Xin, YANG Shengsheng, FENG Zhanzu, CAO Zhou, MA Yali
2015, 32(2): 249-253. doi: 10.11804/NuclPhysRev.32.02.249
The 1.55 μm InGaAsP multi-quantum-well laser diodes with distributed feedback structures were irradiated by electrons and 60Co- rays. The experimental results show the slope efficiency of laser diode is mostly affected by the total ionizing dose produced by charging particles, and the threshold current and the optical power mainly by displacement damage dose. The displacement damage dose methodology was employed to evaluate radiation damage of the laser diodes, and to predict the power
degradations of these diodes in space. The calculated results indicate that the optical powers of the diodes will have more serious degradation for medium Earth orbit than for geosynchronous Earth orbit,due to higher fluence density of high energy electrons in GEO orbits.
K-shell and L-shell Ionization Cross Sections of Ta and Au induced by 1.0 MeV Electron
ZHANG Jianming, SHAO Caojie, LU Rongchun, YU Deyang, ZHANG Yuezhao, WANG Wei, LIU Jun liang, CAI Xiaohong
2015, 32(2): 254-257. doi: 10.11804/NuclPhysRev.32.02.254
Accurate experimental data for atomic inner-shell ionization cross-sections by electrons are of basic importance both in understanding inelastic electron-atom interaction and its application. Up to now, most of available data on this process were mainly concentrated on the low and medium Z atoms by the bombardment of low energy electrons. In present experiments K-shell and L-shell ionization cross-sections of Ta and Au in collisions with 1.0 MeV eleltron were determined by measuring the characteristic X-rays emitted from the target atoms. For the present collision systems the K-shell ionization cross-sections were found to be 13.3 and 10.1 b,and the L-shell ionization cross sections were 554 and 338 b, respectively. The measured K-shell ionization cross sections are in reasonable agreement with the theoretic predictions of Casnati and Hombourger, while L-shell ionization cross sections are consistent with the theoretical results of Soc eld and Born-Bethey.