Quartetting in odd–odd self-conjugate nuclei

Abstract

We provide a description of odd-odd self-conjugate nuclei in the sd shell in a formalism of collective quartets and pairs. Quartets are four-body structures carrying isospin T = 0 while pairs can have either T = 0 or T = 1. Both quartets and pairs are labeled by the angular momentum J and they are chosen so as to describe the lowest states of 20 Ne (quartets) and the lowest T = 0 and T = 1 states of 18 F (pairs). We carry out configuration interaction calculations in spaces built by one quartet and one pair for 22 Na and by two quartets and one pair for 26 Al. The spectra that are generated are in good agreement with the shell model and experimental ones. These calculations confirm the relevance of quartetting in the structure of N = Z nuclei that had already emerged in previous studies of the even-even systems and highlight the role of J > 0 quartets in the composition of the odd-odd spectra.

Quartet structure of N = Z nuclei in a boson formalism: The case of 28Si

“…By quartets we denote here alpha-like four-body correlated structures formed by two protons and two neutrons coupled to total isospin T = 0. Recently, microscopic quartet models have been successfully employed to describe the proton-neutron pairing [7][8][9][10][11][12] as well as general two-body interactions [13][14][15][16] in N = Z nuclei. As a basic outcome, the J = 0 quartet has been found to play a leading role but other low-J quartets have also been found essential to describe the spectra of N = Z nuclei.…”

Isovector and isoscalar pairing in odd–odd N = Z nuclei within a quartet approach

“…In brackets are given the errors relative to the exact results. One can observe that the smallest errors correspond to the approximations (10,11) in which the contribution of the In column 6 are shown the results corresponding to the approximations (12,13) in which the isovector quartet is taken out from the even-even core. We can see that in this case the errors are much bigger than in the case when the isoscalar pairs are neglected.…”

Band-like structures and quartets in deformed N=Z nuclei

“…The use of quartets has not been limited to the analysis of the ground state only. A more elaborate quartet formalism, involving quartets other than the single J = 0, T = 0 one of the QCM approach, has been developed to describe the spectra of N = Z systems [30][31][32].…”

“…A crucial aspect of the QM approach consists in the definition of the quartets to involve in the calculations. In all the cases studied so far we have adopted the criterion of assuming as T = 0 quartets those defining the low-lying eigenstates of the nearest T = 0 one-quartet systems [30][31][32]. While having the advantage of being straightforward, this "static" definition of the quartets is clearly not the most appropriate one since it fully neglects the effect of the Pauli principle on the amplitudes of the quartets when two or more of these quartets have to coexist in the same nucleus.…”