Participation in the S306 Experiment at GSI in January 2009

我们建议研究27，29Ne(N=17，19)，30Na，31 mg，32Al(N=19)，33 Mg，34Al(N=21)丰中子核的基态性质，通过中能(400-500 MeV/A)二次束的库仑分裂，研究N~20附近丰中子核的壳层结构。这是一种与迄今用于研究这些原子核的基态性质的方法完全不同的方法。由达姆施塔特GSI的SIS设施提供的能量为550 MeV/核子的40Ar束流可以通过碎裂获得次级束流。实验将在FRS-LAND-ALADIN装置上进行，通过探测高能(200-500 MeV)的前向聚焦中子、碎片(能量为400-500 MeV/核子的类似射弹)和从激发碎片中产生的跃迁伽马射线，与相应的射束相一致。通过比较实验不变质量分析谱的截面和形状与直接分裂模型的计算结果，可以得到基态性质，即基态组态、自旋以及价中子(S)的占有率。关于壳层结构的信息，特别是Nd3/2-Nf7/2，P3/2，1/2轨道反转的可能性可以推断出来。

We propose to study the ground-state properties of neutron-rich nuclei 27,29Ne (N=17,19), 30Na,31Mg, 32Al (N=19), 33Mg, 34Al ( N=21)), investigating the shell structure of neutron-rich nuclei around N~20, through Coulomb break up of secondary beams at intermediate energy (400-500 MeV/A). This is a completely different method than those which have been used so far to study the ground-state properties of these nuclei. The secondary beams can be obtained by fragmentation of an 40Ar beam at an energy 550 MeV/nucleon delivered by the SIS facility at GSI, Darmstadt. The experiment will be performed at the FRS-LAND-ALADIN setup by detecting forward focussed neutrons of high energy ( 200-500 MeV), fragments (projectile like with energy 400-500 MeV/nucleon) and transition gamma-rays from excited fragments in coincidence with the corresponding projectile. The ground-state properties, i.e., ground state configuration, spin and hence occupation of valence neutron(s) can be obtained by comparing both cross section and shape of the experimental invariant mass analysis spectra with those calculated in a direct-breakup model. Information about the shell structure, particularly, the possibility of an inversion of nd3/2 - nf7/2 , p3/2,1/2 orbitals can be deduced.