从对³⁰F的研究看²⁸O周围的幻数与超流性

Magicity versus Superfluidity around ^{28}O viewed from the Study of ^{30}F.

作者信息

Kahlbow J, Aumann T, Sorlin O, Kondo Y, Nakamura T, Nowacki F, Revel A, Achouri N L, Al Falou H, Atar L, Baba H, Boretzky K, Caesar C, Calvet D, Chae H, Chiga N, Corsi A, Delaunay F, Delbart A, Deshayes Q, Dombrádi Z, Douma C A, Elekes Z, Gašparić I, Gheller J-M, Gibelin J, Gillibert A, Harakeh M N, Hirayama A, Holl M, Horvat A, Horváth Á, Hwang J W, Isobe T, Kalantar-Nayestanaki N, Kawase S, Kim S, Kisamori K, Kobayashi T, Körper D, Koyama S, Kuti I, Lapoux V, Lindberg S, Marqués F M, Masuoka S, Mayer J, Miki K, Murakami T, Najafi M, Nakano K, Nakatsuka N, Nilsson T, Obertelli A, Orr N A, Otsu H, Ozaki T, Panin V, Paschalis S, Rossi D M, Saito A T, Saito T, Sasano M, Sato H, Satou Y, Scheit H, Schindler F, Schrock P, Shikata M, Shimada K, Shimizu Y, Simon H, Sohler D, Stuhl L, Takeuchi S, Tanaka M, Thoennessen M, Törnqvist H, Togano Y, Tomai T, Tscheuschner J, Tsubota J, Uesaka T, Wang H, Yang Z, Yasuda M, Yoneda K

机构信息

Institut für Kernphysik, <a href="https://ror.org/05n911h24">Technische Universität Darmstadt</a>, 64289 Darmstadt, Germany.

<a href="https://ror.org/05tqx4s13">RIKEN Nishina Center</a>, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.

出版信息

Phys Rev Lett. 2024 Aug 23;133(8):082501. doi: 10.1103/PhysRevLett.133.082501.

DOI:10.1103/PhysRevLett.133.082501

PMID:39241734

Abstract

The neutron-rich unbound fluorine isotope ^{30}F_{21} has been observed for the first time by measuring its neutron decay at the SAMURAI spectrometer (RIBF, RIKEN) in the quasifree proton knockout reaction of ^{31}Ne nuclei at 235 MeV/nucleon. The mass and thus one-neutron-separation energy of ^{30}F has been determined to be S_{n}=-472±58(stat)±33(sys) keV from the measurement of its invariant-mass spectrum. The absence of a sharp drop in S_{n}(^{30}F) shows that the "magic" N=20 shell gap is not restored close to ^{28}O, which is in agreement with our shell-model calculations that predict a near degeneracy between the neutron d and fp orbitals, with the 1p_{3/2} and 1p_{1/2} orbitals becoming more bound than the 0f_{7/2} one. This degeneracy and reordering of orbitals has two potential consequences: ^{28}O behaves like a strongly superfluid nucleus with neutron pairs scattering across shells, and both ^{29,31}F appear to be good two-neutron halo-nucleus candidates.

摘要

在日本理化学研究所的放射性同位素束流工厂（RIBF）的SAMURAI光谱仪上，通过测量235 MeV/核子的31Ne核的准自由质子敲出反应中的中子衰变，首次观测到了富含中子的非束缚氟同位素30F21。通过测量其不变质量谱，确定了30F的质量以及单中子分离能为Sn = -472±58(统计)±33(系统) keV。Sn(30F)没有急剧下降，这表明在接近28O时，“幻数”N = 20的壳层间隙没有恢复，这与我们的壳模型计算结果一致，该计算预测中子d和fp轨道近乎简并，1p3/2和1p1/2轨道比0f7/2轨道更束缚。这种轨道的简并和重新排序有两个潜在后果：28O表现得像一个强超流核，中子对在壳层间散射，并且29,31F似乎都是很好的双中子晕核候选体。