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

通过质子非弹性散射研究沿中子滴线的核变形

• 批准号: 15540257
• 负责人: NAKAMURA Takashi
• 金额: $ 2.37万
• 依托单位: Tokyo Institute of Technology
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2003
• 资助国家: 日本
• 起止时间: 2003 至 2004
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-15540257/
• 关键词: Radioactive Beam; Inelastic scattering; Drip-line nuclei; Nuclear Deformation; 中性子ハロー; 魔法数の破れ; 中性子ハロー核; 殻構造の変化

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

本文研究了滴线核^<11>Be、^Be<14>、^<15>B、^<17>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，我们的目的是激发主要的第一激发态，其中有这些核的变形信息。由于极端的中子质子比可能引起核壳层结构的变化（表现为磁性损失），甚至价中子的退耦效应，这类核的形变引起了人们的广泛关注.本文不仅讨论了能用在束γ谱测量的束缚激发态，而且讨论了能用不变质量谱测量的非束缚态.对于后者，我们已经开发了一种新的漂移室，它可以测量角度的弹射器具有非常高的精度（小于0.1度）。我们还发展了一个新的分析双中子事例的方案，这对确定双中子晕核^&lt;1的激发态是必要的 ...更多信息 4&gt;Be。在RIKEN加速器研究所进行了一系列实验，那里有强放射性束。滴线核由抛射产生，通过碎片分离器RIPS破碎和纯化。用上述两种方法求得激发能，并首次观察到了束缚激发态的^ B的1 <st>~ 3激发态<17>和<14>在Ex=1.56 MeV处的粒子衰变阈以上的^ Be的1 ~ 3激发态。在^ B和^ B中产生第一激发态的截面<17><15>表明，与常规值相比，这些核的有效电荷非常小。这可能与相邻核^ C的退耦效应有关<16>。而^<14>Be的第一激发态位于1.56 MeV，低于<12>其2.1 MeV。这表明，^<14>Be比12 Be具有更多的熔化壳层结构，12 Be是最近发现的失去磁性的核。然而，对于12 Be提取的变形参数<14>小于12 Be。这可以理解为恢复外壳稳定性。这一有趣的发现将进一步研究的理论，包括壳熔化或集群性质的这些核。对于其他原子核，我们也观察到了一种新的状态，我们现在正计划使用不同的α靶探针，一种理想的等压线探针。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，我们期望更解耦的情况下，中子独立于质子移动。研究这种非常奇特的激发对于理解非常丰中子核的行为是很重要的。少

项目成果

Y.Yanagisawa,..., T.Nakamura et al.: "The first excited state of 30Ne studied by proton inelastic scattering in reverse kinematics"Physics Letters B. 566. 84-89 (2003)

Y.Yanagisawa,..., T.Nakamura 等人：“通过反向运动学中的质子非弹性散射研究 30Ne 的第一激发态”物理快报 B. 566. 84-89 (2003)

Observation of strong low-lying El strength in the two-neutron halo nucleus ^<11>Li

双中子晕核中强低位El强度的观测^<11>Li

• 发表时间: 2006
• 期刊: Phys. Rev. Lett. (印刷中)
• 作者: T.Nakamura et al.

Anomalously Hindered E2 Strength B(E2,2^+_1 to 0^+)

异常阻碍 E2 强度 B(E2,2^ _1 到 0^ )

• 发表时间: 2004
• 期刊: Phys.Rev.Lett. 92
• 作者: N.Imai;T.Nakamura;T.Motobayashi;et al.
• 通讯作者: et al.

S.Shimoura,..., T.Nakamura et al.: "Isomeric 0+ state in 12Be"Physics Letters B. 560. 31-36 (2003)

S.Shimoura,..., T.Nakamura 等人：“12Be 中的异构 0 态”Physics Letters B. 560. 31-36 (2003)

Isomeric O^+ state in ^<12>Be

^<12>Be 中的异构 O^ 状态

• 发表时间: 2003
• 期刊: Phys. lett. B 560
• 作者: K.Hamada;S.Horata;T.Yukawa;S.Shimoura et al.
• 通讯作者: S.Shimoura et al.