共查询到20条相似文献,搜索用时 31 毫秒
1.
The isospin effect in peripheral heavy-ion collisions was thoroughly investigated within the framework of the Lanzhou quantum molecular dynamics (LQMD) transport model. A coalescence approach was used to recognize the primary fragments formed in nucleus-nucleus collisions. The secondary decay process of these fragments was described using the statistical code GEMINI. The production mechanism and isospin effect of the projectile-like and target-like fragments were analyzed using the combined approach. It was found that the isospin migration from the high-isospin density to the low-density matter occurred in the neutron-rich nuclear reactions, i.e., 48Ca+208Pb, 86Kr+48Ca/208Pb/124Sn, 136Xe+208Pb, 124Sn+124Sn, and 136Xe+136Xe. A hard symmetry energy was available for creating the neutron-rich fragments, particularly in the medium-mass region. The isospin effect of the neutron-to-proton (n/p) ratio of the complex fragments was reduced when the secondary decay process was included. However, a soft symmetry energy enhanced the n/p ratio of the light particles, particularly at kinetic energies greater than 15 MeV/nucleon. 相似文献
2.
Liang JF Shapira D Gross CJ Beene JR Bierman JD Galindo-Uribarri A Gomez del Campo J Hausladen PA Larochelle Y Loveland W Mueller PE Peterson D Radford DC Stracener DW Varner RL 《Physical review letters》2003,91(15):152701
Evaporation residue cross sections have been measured with neutron-rich radioactive 132Sn beams on 64Ni in the vicinity of the Coulomb barrier. The average beam intensity was 2 x 10(4) particles per second and the smallest cross section measured was less than 5 mb. Large sub-barrier fusion enhancement was observed. Coupled-channel calculations taking into account inelastic excitation significantly underpredict the measured cross sections below the barrier. The presence of several neutron transfer channels with large positive Q values suggests that multinucleon transfer may play an important role in enhancing the fusion of 132Sn and 64Ni. 相似文献
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4.
The Constraint Molecular Dynamics approach is illustrated together with calculation on different heavy ion collisions. In particular the charge-mass distribution produced in the collision 124Sn + 64Ni and 112Sn + 58Ni at 35 MeV/nucleon is discussed. By comparing the Y = (N ? Z)/A distributions for fragments produced in central collisions it results that this observable can be sensitive to the dynamic effects induced on the two systems by the different charge/mass ratio. 相似文献
5.
C. W. Beausang A. N. Wilson N. Amzal D. E. Appelbe S. Asztalos P. A. Butler R. M. Clark P. Fallon A. O. Macchiavelli 《Acta Physica Hungarica A》1997,6(1-4):295-298
High-spin states following deep-inelastic multi-nucleon transfer have been studied using the Gammasphere array at LBNL. A64Ni beam was incident upon a thick208Pb target, leading to the population of more than 130 different nuclei. The strongest channels correspond to nuclei close to the projectile and target, although transfer of up to 50 nucleons has been observed. New high-spin states in neutron-rich Fe, Ni and Zn have been observed, indicating that this type of reaction provides a means of exploring neutron-rich nuclei which cannot normally be reached by heavy-ion fusion-evaporation reactions. The data has been searched for superdeformed (SD) states in theA=190–200 region, but as yet no evidence for their presence has been found. 相似文献
6.
G. H. Hovhannisyan A. S. Danagulyan A. R. Balabekyan J. Adam V. G. Kalinnikov V. S. Pronskikh A. A. Solnyshkin V. M. Tsoupko-Sitnikov N. M. Vladimirova 《Physics of Atomic Nuclei》2012,75(2):125-135
The formation cross sections for about 110 products of interaction between a 12C ion beam of energy 2.2 GeV per nucleon and tin targets from the isotopes 112,118,120,124Sn were calculated. Massyield and charge distributions were obtained for 112,118,124Sn targets. An analysis of these charge distributions reveals that the positions of their maxima, Z
p
, are different for targets having different nucleon compositions. The formation cross sections for neutron-rich products
originating from neutron-rich targets are found to increase in all product-mass regions considered in our study. Mass distributions
are compared for proton-, deuteron- and ion-nucleus reactions. 相似文献
7.
The isospin dependence, recently observed in Sn + Sn reactions at
40 MeV/nucleon, is discussed within the framework of two simple nuclear multifragmentation models, namely the site percolation and the nucleation-evaporation models. It is shown that both the models are able to discriminate between 112Sn+ 112Sn and 124Sn+ 124Sn reactions. The nucleation-evaporation model succeeds to
reproduce nicely the experimental data, but the site percolation model fails in doing that, even if the cluster
noncompactive effect is taken into account. The calculations indicate
that the data are originated mainly from
a single source. 相似文献
8.
Feng-Shou Zhang Lie-Wen Chen Wen-Fei Li Zhi-Yuan Zhu 《The European Physical Journal A - Hadrons and Nuclei》2000,9(2):149-152
The squeeze-out flow in reactions of 124Sn + 124Sn and 124Ba + 124Ba at different incident energies for different impact parameters is investigated by means of an isospin-dependent quantum
molecular dynamics model. For the first time, it is found that the more neutron-rich system (124Sn + 124Sn) exhibits weaker squeeze-out flow. This isospin dependence of the squeeze-out flow is shown to mainly result from the isospin
dependence of nucleon-nucleon cross-section and the symmetry energy.
Received: 14 March 2000 / Accepted: 29 September 2000 相似文献
9.
J. F. Liang D. Shapira C. J. Gross R. L. Varner H. Amro J. R. Beene J. D. Bierman A. L. Caraley A. Galindo-Uribarri J. Gomez del Campo P. A. Hausladen K. L. Jones J. J. Kolata Y. Larochelle W. Loveland P. E. Mueller D. Peterson D. C. Radford D. W. Stracener 《The European physical journal. Special topics》2007,150(1):35-36
Evaporation residue and fission cross sections of radioactive
132Sn on 64Ni were measured. Statistical model calculations
using parameters simultaneously fitting stable Sn+64Ni data
reproduce the 132Sn induced reaction very well. A large
sub-barrier fusion
enhancement was observed. The enhancement can be accounted for by
coupled-channels calculations including inelastic excitation of the
projectile and target, and neutron transfer. 相似文献
10.
36Ar+112,124Sn反应中小角关联出射的中等质量碎片(IMF)约化速度关联函数. 结果表明36Ar+124Sn反应系统中的约化速度关联函数在小约化速度处的反关联程度比36Ar+112Sn反应系统中的强, 表现出明显的入射道依赖性. 考察出射粒子对的单核子总动量时, 发现这种差异主要来自于高动量粒子对的贡献. 用三体弹道理论模型MENEKA分别计算了两个系统的IMF发射时标, 在36Ar+112Sn反应系统中约为150fm/c, 而在36Ar+124Sn反应系统中, 约为120fm/c. 同位旋相关的量子分子动力学计算表明, 36Ar+124Sn系统中IMF的发射时间谱比36Ar+112Sn系统略有前移, 相应地, 其中心密度从最高点随时间的下降亦比36Ar+112Sn系统略快. 相似文献
11.
Within the framework of the isospin-dependent quantum molecular dynamics model, along with the GEMINI model, the ~(86)Kr+~(181)Ta reaction at 80, 120 and 160 MeV/nucleon and the ~(78)Kr+~(181)Ta reaction at 160 MeV/nucleon are studied, and the production cross sections of the generated fragments are calculated. More intermediate and large mass fragments can be produced in the reactions with a large range of impact parameter. The production cross sections of nuclei such as the isotopes of Si and P generally decrease with increasing incident energy.Isotopes near the neutron drip line are produced more in the neutron-rich system ~(86)Kr+~(181)Ta. 相似文献
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应用改进的量子分子动力学模型,在严格挑选初始核考虑弹靶结构效应的基础上,研究了近垒和垒上融合反应40,48Ca+90,96Zr. 研究表明: 4个反应的理论计算截面与实验值很好符合; 丰中子反应40Ca+96Zr的垒下融合截面比其他3个反应有明显增强的现象.为了理解丰中子反应40Ca+96Zr与40Ca+90Zr相比垒下融合截面增强,而Ca+96Zr垒下融合截面没有明显增强的原因, 进一步分析了484个反应的融合位垒,中子转移与融合位垒的关系、中子转移与Q值的关系,结果表明: 正反应Q值会引起核子(特别是中子)转移的增强,从而导致动力学融合位垒的下降和垒下融合截面增强. 相似文献
14.
Kohley Z Liang JF Shapira D Varner RL Gross CJ Allmond JM Caraley AL Coello EA Favela F Lagergren K Mueller PE 《Physical review letters》2011,107(20):202701
The fusion excitation functions for radioactive (132)Sn + (58)Ni and stable (130)Te + (58,64)Ni were measured at energies near the Coulomb barrier. The coupling of transfer channels in heavy-ion fusion was examined through a comparison of Sn + Ni and Te + Ni systems, which have large variations in the number of positive Q-value nucleon transfer channels. In contrast with previous experimental comparisons, where increased sub-barrier fusion cross sections were observed in systems with positive Q-value neutron transfer channels, the reduced excitation functions were equivalent for the different Sn + Ni and Te + Ni systems. The present results suggest a dramatically different influence of positive Q-value transfer channels on the fusion process for the Sn + Ni and Te + Ni systems. 相似文献
15.
Yu. E. Penionzhkevich G. G. Adamian N. V. Antonenko 《The European Physical Journal A - Hadrons and Nuclei》2006,27(2):187-190
The production cross sections of neutron-rich isotopes 52, 54, 56, 58, 60Ca in the diffusive nucleon transfer reactions 48Ca + 197Au and 48Ca + 238U at incident energies close to the Coulomb barrier are predicted. The global trend of production cross-section with respect
to the charge (mass) number of target in reactions with 48Ca beam is analysed for the future experiments. 相似文献
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17.
The Efimov(Thomas) trimers in excited ~(12) C nuclei, for which no observation exists yet, are discussed by means of analyzing the experimental data of ~(70(64))Zn(~(64) Ni) + ~(70(64))Zn(~(64) Ni) reactions at the beam energy of E/A = 35 MeV/nucleon. In heavy ion collisions, a-particles interact with each other and can form complex systems such as ~8 Be and ~(12) C. For the 3 a-particle systems,multi-resonance processes give rise to excited levels of ~(12) C. The interaction between any two of the 3 a-particles provides events with one, two or three ~8 Be. Their interfering levels are clearly seen in the minimum relative energy distributions. Events with the three a-particle relative energies consistent with the ground state of ~8 Be are observed with the decrease of the instrumental error for the reconstructed 7.458 MeV excitation level in ~(12) C, which was suggested as the Efimov(Thomas) state. 相似文献
18.
Effect of the momentum dependence of nuclear symmetry potential on the transverse and elliptic flows
Lei Zhang Yuan Gao Yun Du Guang-Hua Zuo Gao-Chan Yong 《The European Physical Journal A - Hadrons and Nuclei》2012,48(3):30
In the framework of the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model, the effect of the momentum dependence
of nuclear symmetry potential on nuclear transverse and elliptic flows in the neutron-rich reaction 132Sn+124Sn at a beam energy of 400MeV/nucleon is studied. We find that the momentum dependence of nuclear symmetry potential affects
the rapidity distribution of the free neutron to proton ratio, the neutron and the proton transverse flows as a function of
rapidity. The momentum dependence of nuclear symmetry potential affects the neutron-proton differential transverse flow more
evidently than the difference of neutron and proton transverse flows as well as the difference of proton and neutron elliptic
flows. It is thus better to probe the symmetry energy by using the difference of neutron and proton flows since the momentum
dependence of nuclear symmetry potential is still an open question. And it is better to probe the momentum dependence of nuclear
symmetry potential by using the neutron-proton differential transverse flow the rapidity distribution of the free neutron
to proton ratio. 相似文献
19.
G. Beier J. Friese W. Henning P. Kienle H. J. Körner W. Wagner W. A. Mayer W. Mayer 《Zeitschrift für Physik A Hadrons and Nuclei》1990,336(2):217-222
Strongly damped collisions were studied in uranium induced reactions on110Pd and124Sn target nuclei near the barrier. The excitation-energy splitting was deduced from binary reaction yields and those in which the heavy fragment undergoes sequential fission. For systems with 87≦Z≦95 for the heavy fragment, the excitation energy is concentrated in the lighter nucleus, at best shared equally. The results indicate a non-equilibrated energy dissipation, and support nucleon exchange based on average single-particle strength functions as the underlying dissipation mechanism at the barrier. 相似文献
20.
An imaginary potential with universal normalization for dissipative processes in heavy-ion reactions
D. Pereira J. Lubian J.R.B. Oliveira D.P. de Sousa L.C. Chamon 《Physics letters. [Part B]》2009,670(4-5):330-335
In this work we present new coupled channel calculations with the São Paulo potential (SPP) as the bare interaction, and an imaginary potential with system and energy independent normalization that has been developed to take into account dissipative processes in heavy-ion reactions. This imaginary potential is based on high-energy nucleon interaction in nuclear medium. Our theoretical predictions for energies up to ≈100 MeV/nucleon agree very well with the experimental data for the p,n+nucleus, 16O + 27Al, 16O + 60Ni, 58Ni + 124Sn, and weakly bound projectile 7Li + 120Sn systems. 相似文献