Low-energy Coulomb excitation of Sr96,98 beams

Abstract

The structure of neutron-rich 96,98 Sr nuclei was investigated by low-energy safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN, with the MINIBALL spectrometer. A rich set of transitional and diagonal E2 matrix elements, including those for non-yrast structures, has been extracted from the differential Coulomb-excitation cross sections. The results support the scenario of a shape transition at N = 60, giving rise to the coexistence of a highly deformed prolate and a spherical configuration in 98 Sr, and are compared to predictions from several theoretical calculations. The experimental data suggest a significant contribution of the triaxal degree of freedom in the ground state of both isotopes. In addition, experimental information on low-lying states in 98 Rb has been obtained.

Quadrupole collectivity in Ca42 from low-energy Coulomb excitation with AGATA

“…Since this information cannot be directly introduced into the GOSIA input files, an indirect method described in Ref. [85] was used: a virtual level of spin and parity 1 + , at arbitrarily chosen 1200-keV excitation energy, has been declared in addition to the known level scheme of 42 Ca, and connected to the 0 + 2 state by a M1 transition. The 1 + M1 0 + 2 was fitted so that the relative intensity of the 0…”

Nuclear-structure studies of exotic nuclei with MINIBALL

“…The excited states in these odd-A nuclei, that form rotational bands built on the ground state, were observed for the first time. The results provide clear-cut evidence for enhanced quadrupole collectivity of the 97,99 Rb nuclei and firmly identify the deformation-driving configuration of the odd proton. Detailed information on the M1 transition strengths in 97 Rb provided concrete experimental evidence for the p…”

“…This shape transition is accompanied by the appearance of low-lying + 0 states that, for < N 60, can be interpreted as a deformed configuration that becomes the ground state at N=60, while the spherical ground-state configuration of the isotopes with < N 60 becomes nonyrast for those with  N 60 (see [95] and references therein). The systematics of the excitation energies of the Clément et al [42,99] Sr underlined their similarity and establishes the shape inversion at N=60. In this work the interpretation of measured reduced E2 matrix elements using a phenomenological two-band mixing model substantiates the weak mixing between prolate and spherical configurations in the wave functions of the + 0 states in 98 Sr, in spite of their proximity in energy.…”

Shell model symmetries

“…In their Table 4 Clement et al [24] show reduced matrix elements. In our Table 5 we show rather the ratio of a given B(E2) to the intraband 0(1) −→ 2(1) B(E2).…”

“…We next make a comparison of the behavior in the Ti isotopes with what occurs in more deformed nuclei. It is convenient to choose the work of Clement et al [24] on 98 Sr because they show several measured B(E2)'s between states in the yrast band and those in the next band. The comparison is somewhat hybrid because we are listing experimental results for Sr and theoretical results for Ti.…”