Title: Ground state properties near the N = 20 and N = 40 islands of inversion
Other Titles: De eigenschappen van grondtoestanden rond het N = 20 en N = 40 eiland van inversie
Authors: Heylen, Hanne
Issue Date: 21-Sep-2016
Abstract: In this work, nuclear spins, magnetic moments, quadrupole moments and mean-square charge radii were measured to explore the changing nuclear structure in the islands of inversion around N = 20 and N = 40. These ground state properties are excellent probes to study the observed structural changes as they are sensitive to the interplay between single-particle and collective effects governing the dynamics in these regions.
Located above the deformed Mg isotopes, the neutron-rich Al (Z = 13) isotopes constitute the northern border of the island of inversion around N = 20. Their structure is investigated in two -NMR/NQR experiments at the LISE-GANIL facility. The quadrupole moment of the 33Al is measured with a 5 times higher precision than the previous value. Only due to this high precision, it could be unambiguously concluded that there is a significant amount of intruder configurations in the ground state wave function, placing 33Al inside rather than outside of the island of inversion. Furthermore, the g-factor and quadrupole moment of the recently discovered 1+ isomer in 34Al is discussed. While so far, 2p-2h (and 4p-4h) excitations are found to dominate the low-energy structure in the island of inversion, this 1+ isomer is proposed to have a 1p-1h configuration. Its g-factor and quadrupole moment, in comparison with the 1+ normal ground state of 32Al, enable the verification of this proposed intruder nature and offer the unique opportunity to study the increase in deformation due to these particular 1p-1h excitations.

The region below 68Ni is characterised by a rapid onset of collectivity. The neutron-rich Mn (Z = 25) isotopes lie in the middle of this region of collectivity, sometimes also called an island of inversion in view of the parallels with the situations around N = 20. Two collinear laser spectroscopy experiments have been performed at ISOLDE-CERN to study the ground state properties along the Mn isotopic chain. In a first experiment, the spins and magnetic moments between N = 26 and N = 39 were extracted. Previously, all spins beyond N = 34 were only tentatively assigned. By our direct measurement we firmly establish a I = 5/2 ground state spin for 59,61,63Mn and a I = 1 low-spin state and I = 4 high-spin state in the 58,60,62,64Mn. Via a comparison of the magnetic moments to large-scale shell model calculations, the
significance of neutron excitations across N = 40 as well as proton excitations across Z = 28 in the structure of the neutron-rich Mn can be established. In a second experiment, the successful application of optical pumping in ISCOOL enabled the measurement of the quadrupole moments of the odd-even 53−63Mn isotopes. The observed rise in quadrupole moments illustrates the development in quadrupole collectivity towards N = 40. In particular, it was demonstrated that both the g9/2 and d5/2 orbitals are necessary to reproduce this collectivity. Additionally, the onset of deformation was confirmed by the mean-square charge radii which show a strong increase towards N = 40. More generally, the results of the two collinear laser spectroscopy experiments in combination with large-scale shell model calculations, enable a systematic
investigation of the evolution of nuclear structure between N = 26 and N = 39.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Nuclear and Radiation Physics Section

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