Monopole strength as a measure of nuclear shape mixing

Abstract

A survey of observed EO transition strength shows that some of the largest strength occurs for transitional nuclei whenever large mixing between almost spherical and largely deformed shapes results. This leads to the conclusion that large EO strength is not an indication of coexisting shapes but of strong mixing between nuclear states with largely different radii. In addition, we discuss the variation of EO transition rates in regions where intruder states become the nuclear ground state.We illustrate this by recent results in the A =100 region concentrating especially on the anomalously large monopoles strength and its variation in the even-even N =60 isotones as compared with the N =58 isotones.

Electric monopole transitions from low energy excitations in nuclei

“…In the present study we explore the relationship between E0 transition strength, ρ 2 (E0), and shape isomerism (or shape coexistence, see, e.g., 5 ) in nuclei. The association of E0 transitions with shape coexistence is a relatively recent development 3,6 . Some preliminary surveys have been made [7][8][9] , but the association between ρ 2 (E0) and different shapes was only qualitative.…”

E0transitions in deformed nuclei

“…The results will depend on the total boson number, N . We will show the results for SU (3) and O(6) in two forms: in terms of a symmetric matrix of ρ 2 (E0) values where the columns and rows are labeled by their quantum numbers, and pictorially in terms of a level scheme diagram of the ground and excited 0 + states and the allowed transitions between them. Figure 2 shows the results for O(6) nuclei for N = 6 bosons.…”

“…Figure 1 illustrates the three dynamical symmetries of the IBA in terms of the symmetry triangle and the allowed E0 transitions to the ground state for the SU(3) and the O(6) symmetries. The lowest excited 0 + states in each corner of the triangle for U(5), SU (3) and O(6) are labeled with their quantum numbers, n d for U(5), (λ, µ) for SU(3) and (σ, τ ) for O (6) where N in the SU(3) and O(6) cases is the total number of bosons. The red and green dots in Fig.…”

“…There have been a number of theoretical treatments of these transitions. Although a consensus on their interpretation has sometimes been lacking [1][2][3][4], it is clear that they are particularly sensitive to changes in nuclear shape, growing rapidly in strength in spherical-deformed shape/phase transition regions. They have been predicted, in the context of the Interacting Boson Approximation (IBA) model [5], to remain large throughout the deformed region [4].…”

“…We start with the dynamical symmetries O(6) and SU (3) [all E0 transitions are identically zero in U(5)] and then look at cases in the interior of the symmetry triangle of the IBA, including a calculation along the arc of regularity [9]. We will do the calculations for different numbers of valence nucleons to check for consistency of the results.…”