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The transfer of neutrons onto 24 Ne has been measured using a reaccelerated radioactive beam of 24 Ne to study the ðd; pÞ reaction in inverse kinematics. The unusual raising of the first 3=2 þ level in 25 Ne and its significance in terms of the migration of the neutron magic number from N ¼ 20 to N ¼ 16 is put on a firm footing by confirmation of this state's identity. The raised 3=2 þ level is observed simultaneously with the intruder negative parity 7=2 À and 3=2 À levels, providing evidence for the reduction in the N ¼ 20 gap. The coincident gamma-ray decays allowed the assignment of spins as well as the transferred orbital angular momentum. The excitation energy of the 3=2 þ state shows that the established USD shell model breaks down well within the sd model space and requires a revised treatment of the proton-neutron monopole interaction. DOI: 10.1103/PhysRevLett.104.192501 PACS numbers: 21.10.Hw, 21.10.Jx, 23.20.Lv, 25.60.Je The monopole part of the nucleon-nucleon interaction is now recognized as having a major effect on nuclear shell structure far from stability [1,2]. The interaction between valence protons and neutrons is sufficient to alter the energies of single-particle levels so that different magic numbers (or shell gaps) appear, and this can substantially affect the collective [3] and magnetic [4] properties and basic quantities such as the lifetime [5]. Nucleon transfer reactions induced by light ions are an established experimental tool for studying single-particle structure [6]. Here we employ the ðd; pÞ reaction in inverse kinematics to explore the disappearance of the N ¼ 20 magic number (and its replacement by N ¼ 16) in the neutron-rich neon isotones. As will be shown, the measurement of the differential cross sections of the light ejectiles plus the coincident gamma decays of the residual nucleus brings a new power to this type of study.Recent work using other techniques has provided evidence for the emergence of N ¼ 16 as a magic number in this region, but has not identified the single-particle structure in an unambiguous manner through measurements of the spectroscopic factors and spins. In a study of the decay of 25 F [7] the increased energy of the 0d 3=2 neutron orbital was inferred. This made use of a preliminary analysis of the present work [8] and concluded that the energy shift was consistent with the monopole effect [7]. In a study of 27 Ne using the ðd; pÞ reaction but without detecting the protons [9], a reduced gap between the 0d 3=2 and higher negative parity orbitals was deduced. This agreed with nucleon removal studies [10]. Finally, in recent studies of 23 O by transfer [11] and 25 O by proton removal [12] the 0d 3=2 state was found to have an increased excitation energy, but the required modifications to the shell-model interaction were not mutually consistent [11,12]. While an extensive review including the emergence of the N ¼ 16 magic number has recently been published [2], further quantitative data are needed in order to understand this monopole effect properly....

An in-beam study of excited states in the transfermium nucleus 252 No has been performed using the recoil separator RITU together with the JUROSPHERE II array at the University of Jyväskylä. This is the second transfermium nucleus studied in an in-beam experiment. Levels up to spin 20 were populated and compared to levels in 254 No. An upbend is seen at a frequency of 200 keV/ប corresponding to spin 16. We also use an improved systematics to connect the energy of the lowest 2 ϩ state with its half-life and find that the deformation of both 252,254 No is slightly larger than previously assumed.

Prompt and delayed ␥ rays from 191,193 Bi have been identified using the recoil-decay tagging, isomer tagging, and recoil gating techniques, resulting in extensive level schemes for both nuclei. Excitation energies of the isomeric 13/ 2 + states have been established and oblate strongly coupled bands built on them have been observed. The nearly spherical 9 / 2 − ground-state bands appear to be crossed by more oblate-deformed lowlying structures. The properties of the bands feeding the 1 / 2 + intruder states indicate some structural change between 193 Bi and 191 Bi. The deformation associated with each of these states has been extracted from total Routhian surface calculations which also reveal the development of prolate minima with decreasing neutron number. B͑M1͒ / B͑E2͒ ratios have been measured for the observed strongly coupled bands in order to resolve the intrinsic excitations. The observed quasiparticle structures in 193 Bi and high-spin isomers both in 193 Bi and 191 Bi are interpreted based on the coupling of the odd proton to the even-even Pb core.