Neutron Halo Structure in exiotic nuclei (^<17>B,^<22>N,^<23>O etc.)

在70A MeV下，测量了^&lt；17&gt；B在^9Be上碎裂后的双中子清除截面(σ_&lt；-2n&gt；)和^&lt；15&gt；B碎片的纵向动量分布。在弹丸静止框架内的分布特征是：^&lt；15&gt；B的半高宽为80±10 MeV/c，σ为0.22±0.05b。数据的Glauber型分析提供了^&lt；17&gt；B中存在两个中子晕结构的明确证据。用透射法测量了能量为77ameV的碳靶上丰中子核的反应截面(σ_R)。σ_R明显增强(1400mb)。根据σ_R的能量依赖关系，结合高能数据，在光学极限近似下，用有限范围的Glauber模型计算得到了^&lt；17&gt；B的密度分布。确定了密度分布中的中子尾对于重现测量的σ_R是必要的。基于核(15&gt；B)加价双中子图的假设，研究了v(2s&lt；1/2&gt；)和v(1d&lt；5/2&gt；)的混合物，不考虑两个中子之间的关联。

The two--neutron removal cross section (σ_<-2n>) and the longitudinal momentum distribution of ^<15>B fragments from the breakup of ^<17>B on ^9Be were measured at 70 A MeV. The distribution in the projectile rest frame is characterized by a FWHM of 80±10 MeV/c for ^<15>B. The σ_<-2n> is found to be 0.22±0.05 b. A Glauber--type analysis of the data provides clear evidence of a two-neutron halo structure in ^<17>B.The reaction cross section (σ_R) for the neutron-rich nucleus ^<17>B on a carbon target has been measured at an energy of 77 AMeV by a transmission method. A large enhancement of σ_R was observed (1400mb). The density distribution of ^<17>B was deduced through the energy dependence of σ_R together with high-energy data using a finite-range Glauber model calculation under an optical limit approximation. It is confirmed that the neutron-tail in the density distribution is necessary for ^<17>B in order to reproduce the measured σ_R. Based on the assumption of a core (^<15>B) plus valence two-neutron picture, the mixture of v (2s_<1/2>) and v (1d_<5/2>) was studied without treating the correlation between two neutrons.