Two-phonon γ-vibrational strength in osmium nuclei

Abstract

Collective E2 strengths were measured to probe the two-phonon ␥-vibrational character of I K ϭ4 4 ϩ states for 188,190 Os. Lifetimes for states with spin up to 8 ϩ of the ground-state band, 6 ϩ of the ␥ band, and the 4 ϩ state of the K ϭ4 ϩ band were measured by the recoil-distance method following Coulomb excitation by a 58 Ni projectile at E lab ϭ275 MeV. These lifetime data are compared with the electromagnetic matrix elements measured by previous Coulomb excitation experiments. The good agreement between these independent measurements supports the conclusion, made by the Coulomb excitation work, that the electromagnetic properties of these osmium nuclei are consistent with the description of ␥-soft collective models. In addition, it supports the evidence that the two-phonon ␥-vibration configuration is the dominant component for the lowest-lying I K ϭ4 4 ϩ states in osmium nuclei.

Microscopic structure of low-lying states inOs188,190,192

“…It was also found that the ratio of the intrinsic E2 matrix elements between the 4 + 3 and the 2 + γ bandhead approaches the harmonic limit [6]. The two-phonon γ -vibrational nature of the 4 + states found further confirmation in recent lifetime measurements, which produced E2 strengths consistent with the data obtained in the Coulomb excitation experiments [7].…”

“…In principle, the strength gets contribution from both the "allowed" transitions involving the one-phonon components |i, K π = 0 + of the QPM state (7) and the "forbidden" transitions from the ground to the twophonon components |[v 1 v 2 ] 0 + . In practice, the two-phonon contribution is negligible, so that the full strength is carried by the one-phonon allowed transitions, whose amplitudes are given by…”

New high-spin isomer and quasiparticle-vibration coupling inIr187

“…In this context, the even-even 186−192 Os isotopes have been the subject of a long-standing controversy regarding the character of their low-lying excited states. In a large number of studies employing different experimental techniques such as Coulomb excitation [1][2][3], (p, p ) and (α,α ) scattering [4][5][6][7], and ( 3 H,α), ( 3 He,d), and (d, 3 He) reactions [8][9][10], apparently conflicting results have been obtained, indicating, respectively, a multiphonon quadrupole, proton two-quasiparticle, and hexadecapole character of the low-lying 4 + 3 states in these nuclei. From the theoretical side, very recently the triaxial rotor model [11], the Bohr-Mottelson collective model for a soft triaxial nucleus [12], and the quasiparticle-phonon model [13] have been employed to shed light on the nature of these states; in particular, the latter study came to the conclusion that the 4 + 3 states are indeed of a mixed nature and that all experimental results can be explained naturally in a consistent way.…”

Structure of theKπ=4+bands inOs186,Phillips1, Garrett2, Iudice3 et al. 2010Phys. Rev. CSelf Cite21010View full textAdd to dashboardCite

“…An earlier single-proton transfer study did not perform angular distributions and published a single spectrum from the 187 Re( 3 He, d) 188 Os reaction at 40 • [7]. The B(E2) values were confirmed through lifetime measurements [19], and they sparked considerable debate [7,20,21] over which component in the wave function is dominant. This debate has been dormant for several years, but recent theoretical developments may provide vital clues to the understanding of the 4 + 3 levels.…”