Single-phonon and multi-phonon excitations of the γ vibration in rotating odd-A nuclei

Masayuki Matsuzaki
Phys. Rev. C 90, 044313 – Published 16 October 2014

Abstract

Background: Collective motions in quantum many-body systems are described as bosonic excitations. Multi-phonon excitations in atomic nuclei, however, were observed very rarely. In particular, the first two-phonon γ vibrational (2γ) excitation in odd-A nuclei was reported in 2006 and only a few have been known so far. Two theoretical calculations for the data on Nb103 were performed, one of which was done by the present author within a limited model space up to 2γ basis states. Quite recently, conspicuously enhanced B(E2)s, reduced E2 transition probabilities, feeding 2γ states were observed in Nb105 and conjectured that their parent states, called band (4), are candidates of 3γ states.

Purpose: In the present work, the model space is enlarged up to 4γ basis states. The purpose is twofold: One is to see how the description of 2γ eigenstates in the previous work is improved, and the other is to examine the existence of collective 3γ eigenstates, and when they exist, study their collectivity through calculating interband B(E2)s.

Method: The particle-vibration coupling model based on the cranking model and the random-phase approximation is used to calculate the vibrational states in rotating odd-A nuclei. Interband B(E2)s are calculated by adopting the method of the generalized intensity relation.

Results: The present model reproduces well the energy spectra and B(E2)s of 0γ2γ states in Nb103 and Nb105. For 3γ states, calculated spectra indicate that the most collective state with the highest K at zero rotation feels strong Coriolis force after rotation sets in and consequently is observed with lowered K, where K is the projection of the angular momentum to the z axis. The calculated states account for the observed enhanced B(E2)s within factors of 2–3.

Conclusions: The present calculation with the enlarged model space reproduces the observed 0γ2γ states well and predicts properties of collective 3γ states. The most collective one is thought to be the main component of the observed band (4) from the analyses of the energy spectra and interband B(E2)s although some mixing with states that are not included in the present model would be possible.

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  • Received 12 June 2014

DOI:https://doi.org/10.1103/PhysRevC.90.044313

©2014 American Physical Society

Authors & Affiliations

Masayuki Matsuzaki*

  • Department of Physics, Fukuoka University of Education, Munakata, Fukuoka 811-4192, Japan

  • *matsuza@fukuoka-edu.ac.jp

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Vol. 90, Iss. 4 — October 2014

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