Shell model calculations within SDPF-U Hamiltonian around N=20 region in "Island of inversion" / Firas Abed Ahmed Al-Ezzi

Firas Abed , Ahmed Al-Ezzi (2022) Shell model calculations within SDPF-U Hamiltonian around N=20 region in "Island of inversion" / Firas Abed Ahmed Al-Ezzi. PhD thesis, Universiti Malaya.

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Abstract

The N=20 island of inversion is a fascinating region of experimental and theoretical studies that consists of three nuclei chains; neon (Ne), sodium (Na), and magnesium (Mg). A feature of this region is the deformation of nuclei in the ground state which is evident during inversion between intruder and normal configurations. The spin-flip interaction, tensor interaction and correlation energy (Ecorr) play a central role in shape deformation and in the vanishing of the N=20 shell gap; thereby leading to an inversion in energy levels. SDPF-U; based on the sd-pf model space with two main shells and seven subshells; was one of the Hamiltonians used to describe and understand the N=20. Restriction was used to reduce the dimensionality of the calculations and to create intruder states. Unmixed intruder configurations (1p-1h), (2p-2h) and (3p-3h) were studied for the N=20 region within the SDPF-U Hamiltonian. Restricted configurations were applied to calculate the low-lying states and the transition probabilities ( ) with effective charges ep=1.32 and en=0.421 for the 32-36Mg chains and ep=1.3 and en=0.537 for the 31,33,35Na chains. The best proton distributions in this work were found to be: (1) (d5/2) -2, (s1/2) +2 in sd-shell for positive-parity in the 32,34,36Mg isotopes, (2) (d5/2) -2, (d3/2) +2 in sd-shell for negative-parity in the 32Mg isotope, (3) (d5/2) -2, (d3/2) +2 in sd-shell for positive-parity in the 33,35Mg isotopes, (4) (d5/2) -2, (s1/2) +2 in sd-shell for negative-parity in the 33,35Mg isotopes, and (5) (d5/2)-1, (d3/2) +1 in sd-shell for positive-parity in the 31,33,35Na isotopes. Energy levels and transition probabilities were then calculated using the OXBASH code and compared with recent experimental data and previous theoretical calculations of different methods and models. The goodness of fit between the theoretical and experimental values confirmed the existence of intruder configurations in these nuclei. The theoretical results validated that an SDPF-U Hamiltonian, with restricted configurations, was able to describe the structure of 32-36Mg and 31,33,35Na nuclei within the N=20 region. Moreover, the SDPF-U Hamiltonian results confirmed the existence of many energy states and suggested other states as well.

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