Department of Physics, Tokyo Institute of Technology, 2-12-1 O-Okayama, Meguro, Tokyo 152-8551, Japan.
Phys Rev Lett. 2009 Dec 31;103(26):262501. doi: 10.1103/PhysRevLett.103.262501. Epub 2009 Dec 22.
The cross sections for single-neutron removal from the very neutron-rich nucleus 31Ne on Pb and C targets have been measured at 230 MeV/nucleon using the RIBF facility at RIKEN. The deduced large Coulomb breakup cross section of 540(70) mb is indicative of a soft E1 excitation. Comparison with direct-breakup model calculations suggests that the valence neutron of 31Ne occupies a low-l orbital (most probably 2p(3/2)) with a small separation energy (S(n) approximately < 0.8 MeV), instead of being predominantly in the 1f(7/2) orbital as expected from the conventional shell ordering. These findings suggest that 31Ne is the heaviest halo system known.
利用 RIKEN 的 RIBF 设施，在 230 MeV/nucleon 的能量下，我们测量了非常中子丰富的核 31Ne 在 Pb 和 C 靶上的单中子转移的横截面积。推断出的大 540(70) mb 的库仑破裂截面表明存在软 E1 激发。与直接破裂模型计算的比较表明，31Ne 的价中子占据一个低能级轨道（很可能是 2p(3/2)），其结合能很小（S(n)约<0.8 MeV），而不是像传统壳层排序所预期的那样主要占据 1f(7/2)轨道。这些发现表明 31Ne 是已知的最重的晕核系统。
