Inversion doublets of reflection-asymmetric clustering in Si28 and their isoscalar monopole and dipole transitions

Abstract

Background: Various cluster states of astrophysical interest are expected to exist in the excited states of 28 Si. However, they have not been identified firmly, because of the experimental and theoretical difficulties. Purpose: To establish the 24 Mg + α, 16 O + 12 C, and 20 Ne + 2α cluster bands, we theoretically search for the negative-parity cluster bands that are paired with the positive-parity bands to constitute the inversion doublets. We also offer the isoscalar monopole and dipole transitions as a promising probe for the clustering. We numerically show that these transition strengths from the ground state to the cluster states are very much enhanced.

Isoscalar monopole and dipole transitions inMg24,Mg26, andSi

“…by the softness of these nuclei and related shape coexistence [4]. The low-energy isoscalar monopole (IS0) and dipole (IS1) states in light nuclei can serve as fingerprints of clustering [5,6] one of the basic features of light nuclei. IS1 states can also deliver important information on some mean-field features, such as vorticity [7][8][9][10][11][12][13][14].…”

Enhanced monopole and dipole transitions in nuclei induced by α cluster structures

“…In addition, we have also calculated the continuum strength of the isoscalar dipole (IS1) transition for the α + 40 Ca system, which has been proposed as a effective probe for the asymmetric cluster system [9]. The matrix element of the IS1 transition is prominently increased in the low excitation region, and this result is similar to the result in the IS0 transition.…”

“…The continuum strength function for the transition from the ground state to the unbound continua, which is induced by the external field, is calculated from the ABC calculation [14]. As for the operator of the external field, we consider the monopole (λ = 0) and dipole (λ = 1) operators, which are basically written in the nucleon degree of freedom like [8,9]…”

“…The latter state corresponds to the negative parity partner of the parity doublet with the ground 0 + state. Recently, the isoscalar (or electric) monopole and dipole transitions have been proposed as effective probes to identify the cluster excitation [8,9]. The monopole transition is strongly increased for the radial excitation in the relative wave function of the α cluster and a resitudal nucleus, while the dipole operator strongly responds to the dipole excitation in asymmetric * e-mail: itomk@kansai-u.ac.jp cluster systems with an α particle plus a heavy core.…”

Clustering Probed by Nuclear Responses

“…Recently, the isoscalar monopole/dipole transitions attract much interest as they may overcome this difficulty. It was shown that these transitions strongly populate the cluster resonances and enable us to investigate their properties [1][2][3][4]6]. As an example of such cases, we have theoretically investigated the cluster resonances in 20 Ne, 44 Ti [4] and 24 Mg [5], which I report in this contribution.…”