重离子碰撞中的对称势翻转

利用同位旋和动量相关的输运模型IBUU,以Sn,Sn同位素在低能与高能碰撞为例,在两种不同的对称势作用下,研究了重离子碰撞中的对称势翻转现象.我们发现从低能到高能在同位旋相分化、发射核子的中-质比、发射核子的双n/p比,中-质微分横向流观测量中均存在对称势翻转现象.对称势翻转效应的研究有利于确定对称能的密度依赖性.

~(126)I高自旋态的识别

利用重离子融合蒸发反应12 2 Sn(11B ,5n2p)布居了双奇核12 6 I的激发态 ,首次建立了具有集体带结构特征的能级纲图 ,其中包括 2 0条新γ跃迁 .所建能级纲图的核素归属指定得到了核反应12 4 Sn(7Li,5n)的交叉支持 .简单讨论了所建带结构的可能组态 .

~(146)Tb的能级结构研究

利用能量为161—175MeV的~(32)S束流,通过反应~(118)Sn(~(32)S,1p3n)~(146)Tb研究了双奇核~(146)Tb的高自旋态能级结构。实验进行了γ射线的激发函数、γ射线的各向异性度、X-γ和γ-γ-t符合测量。基于这些测量结果,建立了激发能达8390kev的~(146)Tb核的能级纲图,其中包括新发现的41条γ射线和新建立的27个能级,并指定了~(146)Tb新发现能级的自旋值。用一个h_(11/2)价质子和一个h_(11/2)~(-1)价中子空穴耦合、πh_(11/2)υh_(11/2)~(-1)与~(146)Gd核实激发态的耦合对~(146)Tb的能级结构进行了定性地讨论。

~(125)Sb高自旋态:粒子-核芯激发耦合

利用在束γ谱学方法,通过~(124)Sn(~7Li,α2n)反应研究了~(125)Sb的激发态,首次建立了~(125)Sb的高自旋能级纲图,其中包括21条新γ跃迁和14个新能级。发现1970,2110和2470 keV3个能级为同质异能态,基于延迟符合测量确定了它们的寿命范围,并确定其自旋、宇称分别为15/2~-,19/2~-和23/2~+。根据粒子-核芯耦合图像和经验壳模型计算解释了~(125)Sb的能级结构,3个同质异能态的组态分别被指定为πg_(7/2)(×)V(h_(11/2)s_(1/2))_(5~-),πg_(7/2)(×)V(h_(11/2)d_(3/2))_(7~-)和πg_(7/2)(×)V(h_(11/2)~2)_(10~+),

丰中子核~(125)Sb的高自旋态(英文)

利用在束γ谱学方法 ,通过1 2 4 Sn( 7Li,α2n)反应首次研究了丰中子核1 2 5Sb的高自旋态 .建立了自旋达 2 3 2 +、激发能至 2 63 7keV的能级纲图 ,其中包括 2 1条新γ跃迁和 1 4个新能级 .在 1 970 ,2 1 1 0和 2 471keV识别出了 3个同质异能态 ,估计了它们的寿命范围 ,并建议分别具有πg7 2 ν(h1 1 2 s1 2 ) ,πg7 2 ν(h1 1 2 d3 2 ) ,πg7 2 ν(h21 1 2 )三准粒子组态 .根据价质子与1 2 4 Sn核芯激发态的耦合讨论了1 2 5Sb的能级结构 .

~(127)I核的新能级纲图(英文)

利用1 2 4 Sn( 7Li,4n) 1 2 7I反应研究了1 2 7I核的在束γ谱 ,建立了包括 2 5个新能级和 52条新γ射线构成的新能级纲图 .将基于πh1 1 2 粒子态 ( 1 1 2 - )的负宇称能级推高到 ( 3 5 2 - ) ,在较重的1 2 7I核中得到了退耦合能级结构 .由于在两个正宇称带ΔI=2能级系列中观测到了强的带间跃迁 ,建议此带的主要成分为g7 2质子的组态 .另外还观测到了两个正宇称ΔI=2和ΔI=1能级系列 ,它们可能基于πd5 2 的单准粒子带和一个 3准粒子带 .

中能核反应的余核测量与分布性质

报道了 30 Me V/u4 0 Ar+112 ,12 4 Sn反应中余核的测量方法和结果。对反应中的余核、裂变碎片以及类弹粒子在平行板雪崩计数器中的不同响应以及各自的几何探测效率进行了 Monte- Carlo模拟。利用平行板雪崩计数器 ,通过 TOF-ΔE的关联成功地鉴别了余核 ,并得到了反应的线性动量分布 ,余核的分布与模拟计算的结果基本一致

化学不稳定性和同位素分布的同位旋效应

采用同位旋相关的量子分子动力学模型 ,研究了在轰击能量为 40MeV u和 10 0MeV u时 ,1 1 2 Sn +1 1 2 Sn和1 2 4Sn +1 2 4Sn反应产物的同位素分布 .发现在 40MeV u时 ,同位素分布与入射体系的同位旋密切相关 ;而在 10 0MeV u时 ,对这两种不同同位旋体系给出几乎相同的同位素分布 .这种同位素分布的能量依赖性为研究化学不稳定性及其与力学不稳定性的竞争提供了新途径

挤出流的同位旋效应

在同位旋相关的量子分子动力学模型框架下 ,研究了碰撞系统12 4Sn +12 4　Sn和12 4Ba + 12 4Ba的挤出流及其同位旋效应 .发现丰中子系统12 4Sn + 12 4Sn表现出较小的挤出流 ,挤出流的这种同位旋相关性主要是由核子 -核子碰撞截面的同位旋相关性所决定的 ,只与对称能微弱相关 .

径向膨胀流的同位旋效应

利用同位旋相关的量子分子动力学模型 ,研究了12 4 Ba +12 4 Ba和12 4 Sn+12 4 Sn两个系统在不同入射能量下对心碰撞的径向膨胀流 .发现丰中子系统12 4 Sn +12 4 Sn的径向膨胀流系统性地小于系统12 4 Ba +12 4 Ba的径向膨胀流 .同时发现这种差别主要来自于核子 -核子碰撞截面的同位旋相关性而几乎与对称能无关

Collective Transverse Flow in Intermediate Energy Heavy-Ion Collisions

Within the hadronic transport model IBUU04, we study the density-dependent symmetry energy by using the neutron-proton differential flow from the Sn-132+Sn-124 reactions at beam energies of 200, 400, 600 and 800MeV per nucleon. The strong effect of the symmetry energy is shown at the incident beam energy of 400 MeV/A. The small medium-effect of the neutron-proton differential flow is also found. We also study the neutron-proton differential flows with impact parameters of 3, 5, 7 fm. It is found that in semi-central collisions the sensitivity of the neutron-proton differential flow to the symmetry energy is larger.

Isoscalar Giant Monopole Resonance in Relativistic Continuum Random Phase Approximation

The isoscalar giant monopole resonance (ISGMR) in nuclei is studied in the framework of a fully consistent relativistic continuum random phase approximation (RCRPA). In this method the contribution of the continuum spectrum to nuclear excitations is treated exactly by the single particle Green's function technique. The negative energy states in the Dirac sea are also included in the single particle Green's function in the no-sea approximation. The single particle Green's function is calculated numerically by a proper product of the regular and irregular solutions of the Dirac equation. The strength distributions in the RCRPA calculations, the inverse energy-weighted sum rule m(-1) and the centroid energy of the ISGMR in Sn-120 and Pb-208 are analysed. Numerical results of the RCRPA are checked with the constrained relativistic mean field model and relativistic random phase approximation with a discretized spectrum in the continuum. Good agreement between them is achieved.

Triton-He-3 relative and differential flows as probes of the nuclear symmetry energy at supra-saturation densities

Using a transport model coupled with a phase-space coalescence afterburner, we study the triton-He-3 (t-He-3) ratio with both relative and differential transverse flows in semicentral Sn-132 + Sn-124 reactions at a beam energy of 400 MeV/nucleon. The neutron-proton ratios with relative and differential flows are also discussed as a reference. We find that similar to the neutron-proton pairs, the t-He-3 pairs also carry interesting information regarding the density dependence of the nuclear symmetry energy. Moreover, the nuclear symmetry energy affects more strongly the t-He-3 relative and differential flows than the pi(-)/pi(+) ratio in the same reaction. The t-He-3 relative flow can be used as a particularly powerful probe of the high-density behavior of the nuclear symmetry energy.

Systematic study of the pi(-)/pi(+) ratio in heavy-ion collisions with the same neutron/proton ratio but different masses

A systematic study of the pi(-)/pi(+) ratio in heavy-ion collisions with the same neutron/proton ratio but different masses can help single out effects of the nuclear mean field on pion production. Based on simulations using the IBUU04 transport model, it is found that the pi(-)/pi(+) ratio in head-on collisions of Ca-48 + Ca-48, Sn-124 + Sn-124, and Au-197 + Au-197 at beam energies from 0.25 to 0.6 GeV/nucleon increases with increasing the system size or decreasing the beam energies. A comprehensive analysis of the dynamical isospin fractionation and the pi(-)/pi(+) ratio as well as their time evolution and spatial distributions demonstrates clearly that the pi(-)/pi(+) ratio is an effective probe of the high-density behavior of the nuclear symmetry energy.

Symmetry energy and isovector giant dipole resonance in finite nuclei

We study the relationship between the properties of the isovector giant dipole resonance of finite nuclei and the symmetry energy in the framework of the relativistic mean field theory with six different parameter sets of nonlinear effective Lagrangian. A strong linear correlation of excited energies of the dipole resonance in finite nuclei and symmetry energy at and below the saturation density is found. This linear correlation leads to the symmetry energy at the saturation density at the interval 33.0MeV <= S(po) <= 37.0 MeV. The comparison to the present experimental data in the soft dipole mode of (132) Sn constrains approximately the symmetry energy at p = 0.1 fm(-3) at the interval 21.2MeV similar to 22.5 MeV. It is proposed that a precise measurement of the soft dipole mode in neutron rich nuclei could set up an important constraint on the equation of state for asymmetric nuclear matter.