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2013 Vol. 30, No. 3

Selection of Symposium on Synthesis and Properties of Superheavy Nuclei in 2012
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Selection of Symposium on Synthesis and Properties of Superheavy Nuclei in 2012
Large Mass Transfer Reaction and Production of Neutron Rich Superheavy Nuclei
WU Xizhen, ZHAO Kai, LI Zhuxia, WANG Ning, TIAN Junlong, ZHANG Yingxun
2013, 30(3): 221-230. doi: 10.11804/NuclPhysRev.30.03.221
Abstract(2034) PDF (876KB)(561)
Abstract:
For elements with Z > 100 only neutron deficient isotopes have been synthesized so far. The “northeast area” of the nuclear map can be reached neither in fusion-fission reactions nor in fragmentation processes.The large mass transfer reactions in near barrier collisions of heavy (U-like) ions seem to be the only reaction mechanism allowing us to produce neutron rich heavy nuclei including those located at the superheavy(SH) island of stability and unexplored area of heavy neutron-rich nuclides. This study is extremely important for nuclear astrophysical investigations and, in particular, for the understanding of the r process. In this paper within the Improved Quantum Molecular Dynamics (ImQMD) model combining with the statistical-evaporation model, the large mass transfer reactions, like 238U+238U have been studied. The charge and mass distributions of transiently formed primary fragments are investigated within the ImQMD model and de-excitation processes of those primary fragments are described by the statistical decay model. The mass distribution of the final products in 238U+238U collisions is obtained and compared with the recent experimental data. Through compared the formation cross sections of transfermium element 106 by three reactions of 136Xe+248Cm, 48Ca+248Cm and 238U+248Cm, it is explored that the large mass transfer reactions, like U+U are very benefit for the production of SH nuclei.
Microscopic Theory on Transport Phenomenon of Nuclear Many-body Systems
YAN Shiwei
2013, 30(3): 231-240. doi: 10.11804/NuclPhysRev.30.03.231
Abstract(1638) PDF (712KB)(518)
Abstract:
In this article, I provide a simple review on conventional methods and models on the transport phenomenon of nuclear many-body systems. By exploiting the basic idea of time-dependent projection operator, I recommend a novel method to derive the transport equation for collective motion which is embedded on the microscopic dynamics of timedependent single-particle motion. It is emphasized that the microscopic dynamics of single-particle motion should play an important role for understanding the dynamics of nuclear reaction and the synthesis mechanisms of new superheavy elements. The numerical results of energy dissipation and entropy production indicate that the collective motion passes through three stages, such as dephasing/decoherence, statistical relaxation and stationary state. The statistical relaxation is a complex anomalous diffusion process in general. With the aid of above analysis and results, a possible way to define the collective and single-particle variables for the realistic nuclear many-body systems is proposed.
Generalized Liquid Drop Model and Its Application
ZHANG Haifei, BAO Xiaojun, WANG Jiamei, HUANG Yin, LI Junqing, ZHANG Hongfei
2013, 30(3): 241-259. doi: 10.11804/NuclPhysRev.30.03.241
Abstract(2931) PDF (945KB)(726)
Abstract:
Recent theoretical achievements and challenges about the fusion and decay properties of heavy and superheavy nuclei are generally introduced. Especially, the Generalized Liquid Drop Model(GLDM) as well as its application are emphatically described. Based on the mass number, proton number and the reaction Q value, the GLDM has taken the mass and charge asymmetry, the shape evolution, the proximity potential, as well as the temperature of nucleus into account, well described the proton radioactivity, the decay, the heavy particle radioactivity, the half life of spontaneous fission of heavy nuclei and superheavy nuclei, and the cross-sections of heavy ion fusion. The competitions between the spontaneous fission and other decay modes such as proton and heavy particle radioactivity, the alpha decay, and so on are also studied.
Beauty and Strangeness in Eigenvalues of Nuclear Shell Model Hamiltonian
ZHAO Yumin
2013, 30(3): 260-267. doi: 10.11804/NuclPhysRev.30.03.260
Abstract(1719) PDF (892KB)(446)
Abstract:
The eigenvalue problem is one of the fundamental issues of sciences. Many research fields have been challenged by diagonalizing huge matrices. The nuclear structure theorists face this problem in studies of medium-heavy
nuclei in terms of the nuclear shell model, in which the configuration space is too gigantic to handle. Thus one usually truncates the nuclear shell model configuration space based on various considerations. Another approach is to make use of super computers by various algorithms, and/or to obtain approximate eigenvalues. In this paper we review our recent efforts in obtaining approximate eigenvalues of the nuclear shell model Hamiltonian, with the focus on our semi-empirical approach and a number of extrapolation approaches towards predicting the lowest eigenvalue, as well as strong correlation between the sorted eigenvalues and the diagonal matrix elements, and so on.
Systematic Investigation on Spectroscopy of Transfermium Nuclei
ZHANG Zhenhua, WEN Kai, HE Xiaotao, ZENG Jinyan, ZHAO Enguang, ZHOU Shangui
2013, 30(3): 268-277. doi: 10.11804/NuclPhysRev.30.03.268
Abstract(2069) PDF (925KB)(460)
Abstract:
Experimental and theoretical studies on the spectroscopy of the transfermium nuclei are briefly reviewed.Recent theoretical progresses made by us is introduced. Moreover, the structure of the superheavy nuclei is investigated.
The rotational spectra in even-even and odd-A nuclei in this mass region are systematically studied by using several empirical formulas. Our result shows that compared with the AB formula and the Harris formula, the ab formula can give
a better description for rotational spectra of ground-state bands in even-even nuclei in this mass region. By fitting the experimental single-particle spectra of the odd-A nuclei in this mass region, a new set of Nilsson parameters is proposed.The rotational bands of the transfermium nuclei are investigated systematically by using a cranked shell model with the pairing correlations treated by a particle number conserving method. The experimental kinematic moments of inertia and angular momentum alignments are reproduced quite well. By analyzing the occupation probability of each cranked Nilsson orbital near the Fermi surface and the contributions of valence orbitals in each major shell to the angular momentum alignment, the upbending mechanism in this mass region could be understood clearly. This new Nilsson parameter set is also used to investigate the shell effects and the microscopic shell correction energies of the superheavy nuclei. The calculated results predict that center of the superheavy island is Z = 120, N = 182.
Tetrahedral Symmetry in Superheavy Nuclei
CHEN Yongshou, GAO Zaochun
2013, 30(3): 278-283. doi: 10.11804/NuclPhysRev.30.03.278
Abstract(1619) PDF (626KB)(392)
Abstract:
The projected energy surface calculations based on the reflection asymmetric shell model predict that nucleus 310126 is the doubly magic nucleus next to 208Pb and has a tetrahedral shape in its ground state.The tetrahedral symmetry-driven quantal effects may lead to an increase of binding energy of the ground state by about 13 MeV with respect to the corresponding spherical shape, indicating the importance of inclusion of the tetrahedral degree of freedom in calculations for the heaviest nuclei. The results show that the tetrahedral symmetry-driven quantal effects can significantly increase the fission barriers and therefore result in increased survival probabilities of superheavy nuclei.
Possible Way to Synthesize Element 119 with Reaction 48Ca+254Es
SHEN Caiwan, Yasuhisa Abe, David Boilley
2013, 30(3): 284-288. doi: 10.11804/NuclPhysRev.30.03.284
Abstract(1586) PDF (697KB)(415)
Abstract:
Two-step model is adopted to analyze the fusion process of heavy-ion reaction 48Ca+254 Es. Based on this model, the fusion process is divided into two consecutive steps, i.e., the sticking step and the formation step, and corresponding sticking probability and formation probability are calculated. Combining the statistical evaporation model for the evaporation stage, the maximum evaporation residue cross section for reaction 48Ca+254 Es is 0.7 pb at 4n, Elab =250.2 MeV.
Systematic Study of Fusion Reactions Leading to Superheavy Nuclei
WANG Ning, ZHAO Kai, TIAN Junlong
2013, 30(3): 289-293. doi: 10.11804/NuclPhysRev.30.03.289
Abstract(2055) PDF (714KB)(493)
Abstract:
The fusion probability in “hot” fusion reactions leading to the synthesis of superheavy nuclei is investigated systematically. The quasi-fission barrier influences the formation of the superheavy nucleus around the “island of stability” in addition to the shell correction. Based on the quasi-fission barrier height obtained with the Skyrme energy-density functional, we propose an analytical expression for the description of the fusion probability, with which the measured evaporation residual cross sections can be reproduced acceptably well. Simultaneously, some special fusion reactions for synthesizing new elements 119 and 120 are studied. The predicted evaporation residual cross sections for 50Ti+249Bk are about 35 fb at energies around the entrance-channel Coulomb barrier. For the fusion reactions synthesizing element 120
with projectiles 54Cr and 58Fe, the cross sections fall to a few femtobarns which seems beyond the limit of the available facilities.
Dynamical Deformation Effects in Fusion Reactions to Produce Superheavy Nuclei
WANG Nan, PENG Jinsong, ZHAO Enguang, ZHOU Shangui
2013, 30(3): 294-298. doi: 10.11804/NuclPhysRev.30.03.294
Abstract(1671) PDF (639KB)(423)
Abstract:
Some aspects in the fusion mechanism for the production of superheavy nuclei are investigated with the dinuclear system model with dynamical potential energy surface. The calculation results about the potential energy surface indicate that the inclusion of nuclear dynamical deformation affects the structure of potential energy surface significantly.The investigation on the fusion probability to synthesize superheavy nuclei indicates that the fusion probability decreases significantly due to the increase of the inner fusion barrier for the inclusion of the nuclear dynamical deformation.
Quasifission in Heavy Ion Fusing Reaction Systems
YU Lin, GAN Zaiguo, HUANG Minghui, ZHANG Hongfei, LI Junqing
2013, 30(3): 299-307. doi: 10.11804/NuclPhysRev.30.03.299
Abstract(1849) PDF (788KB)(384)
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In heavy ion fusion reactions, the quasifission(QF) is competing with fusion, and which is often described by incorporating the Kramers formula(KRA-F) into the master equation(ME) within the Di-Nuclear System(DNS) model. However the KRA-F works well only if the QF barrier is high enough. Presently by taking
the relative distance of nuclei as an independent dynamical variable, the evolution of the DNS towards fusion and QF are both treated as a diffusion process in a consistent way by solving MEs. The validity of the KRA-F is thus
checked. Furthermore, the dynamical deformation and the nucleon transfer in heavy ion fusion reaction process are viewed simultaneously as a diffusion process, and are treated by solving a set of MEs with the variables of the
quadrupole deformation of each nucleus and the mass asymmetry variable in the potential energy surface(PES) of the system. The distinct influence of the dynamical deformation on the QF mass yield distribution is discussed,and the experimental observations can be well reproduced by the calculation.
Hindered α-transitions in Odd-Z Superheavy Nuclei
XU Chang, REN Zhongzhou
2013, 30(3): 308-311. doi: 10.11804/NuclPhysRev.30.03.308
Abstract(1964) PDF (538KB)(410)
Abstract:
We investigate the α-transition of odd-Z superheavy nuclei by the density-dependent cluster model (DDCM). The microscopic nuclear potential between the -particle and the daughter nucleus is evaluated numerically from the double-folding model with the standard M3Y nucleon-nucleon interaction. The Coulomb potential is also obtained from the double-folding integral of the proton-proton Coulomb interaction with the charge density distributions of α-particle and daughter nucleus. From our calculations, enhanced stability against
α-decays is found for the odd-Z superheavy nuclei due to the hindrance effect of non-zero angular momentum and the small preformation factor of the -particle.
Investigation of Rotational Properties in Even-Even Nobelium Isotopes
WANG Hualei, JIANG Jinge, LIU Minliang
2013, 30(3): 312-317. doi: 10.11804/NuclPhysRev.30.03.312
Abstract(1683) PDF (741KB)(377)
Abstract:
The rotational properties of the synthesized even-even 248-264No isotopes have been investigated by means of total Routhian surface calculations. The calculated ground-state properties (e.g. β2; β4) are in agreement with previous calculations. The behaviors of moment of inertia of 252,254No are well reproduced by our calculations. The systematic upbending in moment of inertia is attributed to band crossing. It is found that the j15/2 neutron rotation-alignment is preferred for the lighter No isotopes, but the i13/2 proton alignment is favored in the heavier ones.
Competition between Decay and Spontaneous Fission in 292-310122 Isotopes
BAO Xiaojun, ZHANG Haifei, LI Junqing, ZHANG Hongfei
2013, 30(3): 318-323. doi: 10.11804/NuclPhysRev.30.03.318
Abstract(1759) PDF (627KB)(458)
Abstract:
Based on the framework of the Generalized Liquid Droplet Model (GLDM), alpha decay and spontaneous fission half-lives for 292-310122 isotopes are studied. The calculation of the basic inputs which only need the two fragment
mass numbers, charge numbers and the Q value. GLDM can describe alpha decay and spontaneous fission the nuclei. It is found that the alpha decay is the dominant mode of decay for isotopes with mass number A < 308, and for those with A > 308 spontaneous fission is dominant. The demarcation between alpha decay and spontaneous fission is at 308122, which shows the presence of a spherical neutron shell closure at N = 184.
Effect of Isospin Dependent Cluster Recognition on Observables in Heavy Ion Collisions
ZHANG Yingxun, LI Zhuxia, ZHOU Chengshuang, TSANG M.B.
2013, 30(3): 324-330. doi: 10.11804/NuclPhysRev.30.03.324
Abstract(1572) PDF (712KB)(397)
Abstract:
We introduce isospin dependence in the cluster recognition algorithms used in the Quantum Molecular Dynamics model to describe fragment formation in heavy ion collisions. This change reduces the yields of emitted nucleons and enhances the yields of fragments, especially for heavier fragments. The enhancement of neutron-rich lighter fragments mainly occurs at mid-rapidity. Consequently, isospin dependent observables, such as isotope distributions, yield ratios of n/p,t/3He, Rmid yield and isoscaling parameters are affected. We also investigate how equilibration in heavy ion collisions is affected by this change.
Systematic Studies on Transport Process of Heavy-ion Collisions at INDRA Energies and Detection of Symmetry Energy
LI Qingfeng, GUO Chenchen, WANG Yongjia
2013, 30(3): 331-338. doi: 10.11804/NuclPhysRev.30.03.331
Abstract(1997) PDF (838KB)(440)
Abstract:
The terms of initialization, equation of state (EoS), and two-body collision in the updated ultrarelativistic quantum molecular dynamics (UrQMD) model are examined in details so as to systematically study the collective flows and the nuclear stopping of free nucleons and light clusters from heavy-ion collisions at INDRA energies. It is seen that at INDRA energies the dynamic transport with a soft EoS with momentum dependence and with the momentum-modified density-dependent nucleon-nucleon elastic cross sections describes the directed flow exhibited by hydrogen isotopes (Z= 1) emitted at midrapidity fairly well. The sensitivity of the balance energy (Ebal) of the directed flow to the strength parameter of the density dependence of symmetry potential energy is further studied with the same parameter set. It is found that the Ebal of neutrons from HICs is particularly sensitive to the density dependence of the symmetry potential energy, while that of protons is not. And, the initial neutron/proton ratio dependence of the balance energy of neutrons from Sn isotopes can be taken as a useful probe to constrain the stiffness of the nuclear symmetry energy.
Excitation Energy Dependence of Level-density Parameters and Decay Properties of Heavy Nuclei
YE Wei
2013, 30(3): 339-344. doi: 10.11804/NuclPhysRev.30.03.339
Abstract(1621) PDF (709KB)(422)
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Based on the stochastic approach to fission, we have demonstrated that the ratio of level-density parameters at saddle to that at ground-state configuration, af/an, plays a significant role in the decay of an excited nucleus. It modifies not only the sensitivity of evaporation residue cross section and its spin distributions
to nuclear friction, but also the dissipation properties of hot nuclei. Furthermore, we find that af/an as a function of excitation energy appreciably affects the evolution of excitation energy at scission with the friction strength. A consequence of a change of af /an with E* on the stability of superheavy nuclei and on modelling de-excitation processes of spallation reactions is indicated.
Quantum Phase Transitional Patterns of Nuclei
DAI Lianrong, WANG Lixing, PAN Feng, ZHONG Weiwei, LIU Qi
2013, 30(3): 345-351. doi: 10.11804/NuclPhysRev.30.03.345
Abstract(1749) PDF (749KB)(371)
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With the framework of Interacting Boson Model(IBM), transitional patterns from the spherical to the axially deformed limit of the IBM with a schematic Hamiltonian are studied by replacing the SU(3) quadrupole-quadrupole term with O(6) cubic interaction. But, we use the two schemes to investigate some energy ratios and B(E2) ratios for different bosons N = 8 and N = 20. The results show that with the increasing of the numbers of bosons, the transitional behaviors can be enhanced; the transitional behaviors are very similar in the two schemes. However, there are some distinctive differences for some quantities across the entire transitional region, such as energy levels and ratios, B(E2) values and ratios, and expectation values of the shape variables. Generally speaking, the transition is smoother and the nuclear shape is less well defined in the new scheme. Then we apply the two schemes to the critical point symmetry candidate, such as 152Sm, and find the overall fitting quality of the UQ scheme is better than that of the U(5)-SU(3) scheme, especially for the inter-band E2 transitions in 152Sm.
On Nuclear Temperature in Heavy-ion Collisions
SU Jun, ZHANG Fengshou
2013, 30(3): 352-358. doi: 10.11804/NuclPhysRev.30.03.352
Abstract(1646) PDF (690KB)(412)
Abstract:
Nuclear thermometers based on different approaches are reviewed. Due to the different basic assumptions of these methods, the nuclear temperatures extracted by different thermometer approaches are not consistent. Moreover,
several problems which make the extraction of the nuclear temperatures even more difficult are discussed. The nuclear thermometers based on different kinetic approaches are compared. The nuclear temperatures extracted by methodsbased on quantum (Fermi-Dirac) kinetic approaches are compared to the double ratio temperatures THe; Li. Perspectives for future investigations of the thermal temperature are given.
Research on r-mode Instability in Hot Neutron Star
YAN Jing, WEN Dehua
2013, 30(3): 359-363. doi: 10.11804/NuclPhysRev.30.03.359
Abstract(1752) PDF (679KB)(385)
Abstract:
Theoritically, instable r-mode in neutron star may radiate detectable gravitational waves. In this work,considering the non-Newtonian gravity proposed in the grand unification theories, we numerically calculate the CFS instabilities of r-mode s in the hot neutron stars by using an equation of state with super-soft symmetry energies. The changes of the gravitational radiation time scales and the viscous time scales versus the stellar temperatures are obtained.And according to the constraint of the neutron star observation on the parameter of non-Newtonian gravity, the constraint on the boundary of the instability window is also given. It is found that a stronger non-Newtonian gravity corresponds with a wider r-mode instability window. These results may provide interesting reference for the gravitational wave detection.
Investigating Deformation Dependence of Nuclear Dissipation Based on Pathwise Analysis Method
MAO Yingchen, WAN Suyu, LIU Rui, DING Yang, ZHANG Minling, LÜ You, LIU Xin
2013, 30(3): 364-368. doi: 10.11804/NuclPhysRev.30.03.364
Abstract(1387) PDF (718KB)(401)
Abstract:
Within a certain deformation dependence of nuclear dissipation (DDND), the simulation results about the deexcitation process of 200Pb show that the prescission neutron multiplicities decrease with increasing deformation dependence of level density parameter (DDLDP). Moreover, this pattern is determined by the emission of prescission neutron in the first period of nuclear fission. On the other hand, all of the results from two kinds of different DDNDs can reproduce the experiment data perfectly with a certain DDLDP. In order to illustrate those phenomena, the pathwise analysis method (PAM) is presented in this paper. In the PAM, nuclear dissipation is treated as the damping force on the elongation dimension, whereas the fission dynamics process results from the competition between damping force and the driving force stemming from the nuclear free energy. The prescission neutron multiplicity in the deexcitation process of 200Pb is analyzed, and the results point out that the DDLDP needs to be taken into account in studying the DDND.
Focal Plane Detection System of Gas-filled Recoil Separator in Lanzhou
YANG Huabin, YU Lin, HUANG Tianheng, ZHANG Zhiyuan, MA Long, HUANG Minghui, LI Guangshun, WU Xiaolei, GAN Zaiguo
2013, 30(3): 369-373. doi: 10.11804/NuclPhysRev.30.03.369
Abstract(1728) PDF (734KB)(422)
Abstract:
A new designed focal plane detection system was mounted at the gas-filled recoil separator at Institute of Modern Physics, Chinese Academy of Sciences, which consisted of a time-of-flight (TOF) detector, a silicon-box (Sibox) detector array and a silicon veto detector. Three position sensitive silicon detectors (PSSD) were surrounded by eight side silicon detectors (SSD) without position sensitive, forming a box of the detector open from the front side. The detection efficiency for -decays of implanted nuclei was about 80%. The anticoincidence condition for the signals from the TOF detector and Si-box detector array was used to distinguish between the pulses originating from the implanted nuclei and their -decays. The veto detector information was used to discriminate events due to high-energy charged particles.External energy calibration and position calibration of PSSD are described concisely in this work. This system
has been used in experiments of 40Ca+175Lu and 40Ca+169Tm. Clean a-decay spectra obtained in these reactions indicated the detection system has a good performance in background suppression. Evaporation residues can be identified by the energy-time-position correlation method. On the whole, the new designed focal plane detection system has achieved thedesign requirements.
Study on Mass Distribution of n+233U Fission with Phenomenological Model
LIU Lile, SHU Nengchuan, LIU Tingjin, SUN Zhengjun, WU Xizhen, CHEN Yongjing, QIAN Jing
2013, 30(3): 374-378. doi: 10.11804/NuclPhysRev.30.03.374
Abstract(1696) PDF (715KB)(462)
Abstract:
Present model was based upon Brosa model, where macro energy,shell effect energy and its decreasing with system temperature were considered and parameterized. 3 sets of model parameters were obtained by fitting to 3 groups of evaluated experimental data, respectively, where the groups were classified by measured method: radiochemistry (RA) method, double kinetic energy (KE) method, and both (ALL). All the 3 sets of parameters could well reproduce the
measured mass distributions on different energies, except the KE set on 14 MeV. The result shows the mass distributions mainly had 4 trend turning points, above which the yield decreasing and below which the yield increasing with energy.The sum of the 1st and 4th (or 2nd and 3rd) point positions was equal to the compound nuclei mass approximately. And the 3rd point was kept at ~132 constantly for different fission systems n+233 U, n+235U, n+233Pu.
Comparison Evaluation for Yields of n+232Th Fission
SHU Nengchuan, LIU Lile, LIU Tingjin, WU Haicheng, CHEN Yongjing, QIAN Jing, SUN Zhengjun
2013, 30(3): 379-383. doi: 10.11804/NuclPhysRev.30.03.379
Abstract(1874) PDF (667KB)(439)
Abstract:
The yields of n+232Th fission are important in study of the Th/U fuel cycle. Based upon the evaluated nuclear data libraries and recent experimental data,comparison and evaluation for yield mass distribution and cumulative
yield were performed for those products are needed and important in reactor calculations,including 95Mo,99Tc,101Ru,103Rh,109Ag,133Cs,147Sm,149Sm,150Sm,151Sm,152Sm,143Nd,145Nd adn 153Eu etc. Adjustments were made for 133Cs, 152Sm and 153En which have discrepancies among the libraries. Database for n+233Th fission yield is recommended as a part of CENDL update.