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

我们研究了滴线核Be、B、B、C和C在质子靶和碳靶上的非弹性散射。在这项研究中，我们的目标是主要激发第一激发态，它包含了这些核的形变信息。由于极端的中质子比可能引起以磁性损失为代表的核壳层结构的变化，甚至价中子的去耦合效应，这种核的形变引起了人们的极大关注。在本研究中，不仅可以用在束伽马能谱测量束缚激发态，而且可以用不变质量谱测量非束缚态。对于后者，我们开发了一种新的漂移室，它可以非常高的精度(小于0.1度)测量抛射体的角度。我们还发展了一种分析双中子事件的新方案，这对于确定双中子晕核…中的激发态是必要的更多的实验是在RIKEN加速器研究设施进行的，那里有强辐射束可用。滴状核是通过投射、碎裂和碎片分离器RIP纯化而成的。用上述方法得到了激发能。在Ex=1.56 MeV时，我们首次观察到束缚激发态中^&lt；17&gt；B和^&lt；14&gt；的1^&lt；st&gt；激发态正好高于粒子衰变阈值。产生第一激发态的截面表明，这些原子核的有效电荷与常规值相比非常小。这可能与相邻核^&lt；16&gt；C的解耦效应有关。对于^&lt；14&gt；Be，第一激发态位于1.56 MeV，低于^&lt；12&gt；Be的2.1 MeV。这表明14Be比12Be具有更多的熔化壳结构，12Be最近被发现是一个失去磁性的核。然而，14&gt；Be的变形参数比12Be的小。这可能被理解为壳体稳定性的恢复。这一有趣的发现将用包括这些原子核的壳层熔化或团簇性质在内的理论来进一步研究。对于其他原子核，我们也观察到了一种新的状态。我们现在计划使用阿尔法靶的不同探测器，一种理想的等标量探测器。这可能会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，我们预计会出现更多的去耦合情况，即中子的运动不依赖于质子。研究这种非常奇特的激发对于理解非常富含中子的核的行为很重要。较少

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