We report on the first determination of the nuclear ground-state spin of 33Mg, I=3/2, and its magnetic moment, mu= -0.7456(5) mu(N), by combining laser spectroscopy with nuclear magnetic resonance techniques. These values are inconsistent with an earlier suggested 1 particle-1 hole configuration and provide evidence for a 2 particle-2 hole intruder ground state with negative parity. The results are in agreement with an odd-neutron occupation of the 3/2 [321] Nilsson orbital at a large prolate deformation. The discussion emphasizes the need of further theoretical and experimental investigation of the island of inversion, a region previously thought to be well understood.
Charge radii of all magnesium isotopes in the sd shell have been measured, revealing evolution of the nuclear shape throughout two prominent regions of assumed deformation centered on (24)Mg and (32)Mg. A striking correspondence is found between the nuclear charge radius and the neutron shell structure. The importance of cluster configurations towards N=8 and collectivity near N=20 is discussed in the framework of the fermionic molecular dynamics model. These essential results have been made possible by the first application of laser-induced nuclear orientation for isotope shift measurements.
We report the first confirmation of the predicted inversion between the 2p 3=2 and 1f 5=2 nuclear states in the g 9=2 midshell. This was achieved at the ISOLDE facility, by using a combination of insource laser spectroscopy and collinear laser spectroscopy on the ground states of 71;73;75 Cu, which measured the nuclear spin and magnetic moments. Much of the current effort in nuclear physics is focused on determining how the nuclear shell structure is changing in neutron-rich nuclei. This has been triggered by the observation of unexpected phenomena in several neutronrich isotopes, since radioactive ion beams of such nuclei became available more than three decades ago. In the lighter elements (e.g., He, Li, Be), neutron halos and skins were observed. Around the neutron-rich 32 Mg region an ''island of inversion'' was discovered. In the neutron-rich region towards doubly magic 78 Ni, a sudden drop in the position of the first excited 5=2 À state in 71;73 Cu isotopes was observed more than a decade ago [1]. The lowering of the 5=2 À energy from above 1 MeV in 69 Cu to 166 keV in 73 Cu suggested that this state might become the ground state in 75 Cu. The migration of this level, associated with the occupation of the 1f 5=2 single-particle orbital, was attributed to a strong attractive monopole interaction that becomes active when neutrons occupy the 1g 9=2 orbital [2]. Such monopole interactions exist also in near-stable nuclei, but their impact on the evolution of shell structure and shell gaps in far-from-stability nuclei remained unnoticed until recently [3]. Also in other neutron-rich regions dramatic monopole shifts were observed when valence neutrons and protons are occupying orbits having their orbital and spin angular momentum, respectively, aligned and antialigned. It is now understood that one of the physics mechanisms driving these monopole shifts is the tensor part of the residual nucleon-nucleon interaction [4]. A steep lowering of the 1=2 À level from about 1 MeV in 69 Cu down to 135 keV in 73 Cu has also been observed [5,6]. Thus this level is also a potential ground-state candidate in 75 Cu. While most shell-model interactions do reproduce a lowering of the 5=2 À level and predict an inversion with the normal 3=2 À ground state somewhere between 73 Cu and 79 Cu [4,[7][8][9][10], none of them reproduce the lowering of the 1=2 À state. Some significant physics mechanism is either omitted or seriously underestimated in each of the recently developed shell-model interactions. Therefore, experimental establishment of ground-and excited-state nuclear spins and the properties of their wave function (through spectroscopic factors, magnetic moments, transition moments, etc.) is a crucial step in PRL 103,
Measurements of the ground-state nuclear spins and magnetic and quadrupole moments of the copper isotopes from 61 Cu up to 75 Cu are reported. The experiments were performed at the CERN online isotope mass separator (ISOLDE) facility, using the technique of collinear laser spectroscopy. The trend in the magnetic moments between the N = 28 and N = 50 shell closures is reasonably reproduced by large-scale shell-model calculations starting from a 56 Ni core. The quadrupole moments reveal a strong polarization of the underlying Ni core when the neutron shell is opened, which is, however, strongly reduced at N = 40 due to the parity change between the pf and g orbits. No enhanced core polarization is seen beyond N = 40. Deviations between measured and calculated moments are attributed to the softness of the 56 Ni core and weakening of the Z = 28 and N = 28 shell gaps.
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