Study of Structure of Light Extremely Neutron-Rich Nuclei and Their Anomalous Properties

我们沿着这个提议研究了三个主题：(I)研究丰中子核结构的理论发展。(Ii)对^&lt；11&gt；Li反常性质的理解。(3)极富中子核中电偶极子模式的研究。对于第一个主题，文献[1]提出了团簇-轨道壳模型。1和5，在描述这样一个松散耦合的富中子核系统方面被证明是强有力的，并成为研究中子滴线核的基础。7)。该模型可望适用于文献[1]中的α团簇形成机制等问题。3和9.在第二个主题中，我们首先显示在参考文献[1]中。7在我们的模型中，我们成功地理解了^&lt；11&gt；Li的一些反常现象，如极大的半径和伴随着中子晕的密度分布，并在文献[1]中引入。8团簇模型的观点，以便更好地描述解释^&lt；11&gt；Li的结合机制所需的两中子对关联。对于第三个主题，我们在文献[1]中同时考察了流体力学模型和微观模型。2，4和6，表明极富中子核的E_1强度在低激发能下是碎裂的。由于我们已经很好地了解了^&lt；11&gt；Li的基态性质，现在我们扩展了团簇轨道壳模型来寻找^&lt；11&gt；Li中的软电偶极子模。初步结果非常令人鼓舞，似乎解释了在使用放射性核束的高能重离子碰撞中观察到的电磁离解截面的增强。

We have studied three subjects along the proposal: (i) A theoretical development to study the structure of neutron-rich nuclei. (ii) The understanding of the anomalous properties of ^<11>Li. (iii) The investigation of the electric dipole mode in extremely neutron-rich nuclei. Regarding the first subject the cluster-orbital shell model, proposed in refs. 1 and 5, has proven to be powerful in describing such a loosely coupled system as neutron-rich nuclei and become a basis of the study of the neutron dripline nucleus ^<11>Li,(ref. 7). The model is expected to be applicable for such problems as the mechanism of alpha cluster formation in nuclei as done in refs. 3 and 9. In the second subject we have first shown in ref. 7 that some of the anomaly of ^<11>Li, e.g., the extremely large radius and the density distribution with the neutron halo, are successfully understood in our model and then introduced in ref. 8 the cluster model point of view in order to better describe the two-neutron pair correlation that is needed to explain the binding mechanism of ^<11>Li. For the third subject we have examined both hydrodynamical and microscopic models in refs. 2, 4, and 6 to show that the E1 strength of the extremely neutron-rich nuclei are fragmented at low excitation energy. Since we have understood the ground state properties of ^<11>Li fairly well, we are now extending the cluster-orbital shell model to look,for the soft electric dipole mode in ^<11>Li. A preliminary result is very encouraging and appears to account for the enhancement of the electromagnetic dissociation cross section observed in high-energy heavy-ion collisions using radioactive nuclear beams.