Study of nuclear deformation along the neutron drip line via proton inelastic scattering

我们已经研究了滴线核，^<11>Be, ^<14>Be, ^< 15b> B, ^< 17b> B, ^< 18>c和^< 19>c在质子靶和碳靶上的非弹性散射。在这项研究中，我们的目标主要是激发第一激发态，它具有这些原子核变形的信息。由于极端的中子质子比可能引起以磁性损失为代表的核壳结构的变化，甚至对价中子的解耦效应，这类原子核的变形引起了人们的广泛关注。在本研究中，不仅可以用束内伽马能谱测量束缚激发态，而且可以用不变质谱测量非束缚态。对于后者，我们开发了一种新的漂移室，它可以以非常高的精度（小于0.1度）测量弹射角。我们还开发了一种分析双中子事件的新方案，这对于确定双中子晕核^<1…More 4>Be的激发态至关重要。一系列的实验在RIKEN的加速器研究设施中进行，在那里可以获得强烈的放射性光束。滴线核由弹丸产生，经碎片分离机RIPS分离纯化。激发能可以用上述两种方法求得。我们首次观测到^<17>B在束缚激发态中的1^<st>激发态，以及^<14>Be在Ex=1.56 MeV时刚好超过粒子衰变阈值。^<17>B和^<15>B中产生第一激发态的截面表明，与常规值相比，这些原子核的有效电荷非常小。这可能与邻核^<16>C的去耦效应有关。^<14>Be的第一激发态位于1.56 MeV，低于^<12>Be的2.1 MeV。这表明^<14>Be比12Be有更多的熔化壳结构，12Be最近被发现是一个魔法丢失的核。而^<14>Be时提取的变形参数小于12Be时提取的变形参数。这可以理解为壳稳定性的恢复。这一有趣的发现将被进一步研究，包括这些核的壳熔化或团簇性质的理论。对于其他的原子核，我们也观察到了一个新的状态。我们现在计划使用不同的α目标探针，一种理想的等标量探针。这可以澄清中子分布和质子分布之间的形状差异。对于非常极端的中子/质子比，我们期望更多的解耦情况，即中子独立于质子运动。研究这种非常奇特的激发对于理解富含中子的原子核的行为是很重要的。少

We have studied inelastic scatterings of drip-line nuclei, ^<11>Be, ^<14>Be, ^<15>B, ^<17>B, ^<18>C and ^<19>C on a proton target as well as on a carbon target. In this study we aimed at exciting primarily the first excited state, which has information of deformation of these nuclei. The deformation of such nuclei have attracted much attention since the extreme neutron to proton ratio may cause the change of nuclear shell structures represented by the magicity loss, or even the decoupling effect on the valence neutrons.In this study, not only the bound excited states which can be measured by in-beam gamma spectroscopy, but also the unbound states which can be reached by the invariant mass spectroscopy. For the latter, we have developed a new drift chamber which can measure angles of an ejectile with very high accuracy (less than 0.1 deg). We have also developed a new scheme of analyzing two-neutron events, which was essential to specify the excited state in two-neutron halo nucleus ^<1 … More 4>Be.A series of experiments were performed at RIKEN accelerator Research facility, where the intense radioactive beam is available. The drip-line nuclei were produced by the projectile, fragmentation and purified through the fragment separator RIPS. The excitation energy was obtained either by the method mentioned above.We have observed for the first time the 1^<st> excited state of ^<17>B in the bound excited state and that of ^<14>Be just above the particle decay threshold at Ex=1.56 MeV. The cross sections for producing the first excited states in ^<17>B and ^<15>B suggest that the effective charges for these nuclei are extremely small compared to the conventional value. This may be related to the decoupling effect which was found for the neighboring nucleus ^<16>C. As for ^<14>Be, the first excited states located at 1.56 MeV, lower than that of ^<12>Be at 2.1 MeV. This suggests that the ^<14>Be has even more melted shell structure than the case of 12Be, which was recently found as a magicity-lost nucleus. However, the deformation parameter extracted for ^<14>Be was smaller than that of 12Be. This may be understood as a restoration of shell stability. This interesting findings are to be further studied with theories including the shell melting or cluster nature of these nuclei. For other nuclei, we have also observed a new state as well.We are now planning to use the different probe of alpha target, an ideal isoscalar probe. This may clarify the shape difference between the neutron distribution and the proton distribution. For the very extreme neutron/proton ratios, we expect more decoupled situation where neutrons moves independently of protons. Studies of such very exotic excitation is important to understand the behavior of very neutron rich nuclei. Less