Ⅱ-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 47 (2014)

Skyrme-RPA calculation for octupole vibrations of rotatingsuperdeformed nuclei
M. Yamagami, ∗1 and K. Matsuyanagi∗2
fectively treat the conﬁgurations involving unboundsingle-particle states.
We show the isoscalar octupole transition strengths
for K π = 0− and 1− excitations of the triaxial SD stateof 44 Ti in Figs. 1 and 2. The results with ωrot = 0.0
and 0.6 MeV/h̄ are compared.
In the K π = 1− case, an octupole instability ofthe SD yrast states toward a reﬂection-asymmetricshape (banana-like shape) is suggested to take place at
ωrot > 0.6 MeV/h̄ (corresponding to the total angularmomentum I > 5h̄) because of the Coriolis eﬀect.

The superdeformed (SD) shell structure is signiﬁcantly diﬀerent from that of normal deformation. Eachmajor shell at the SD shape consists of about equal
numbers of positive- and negative-parity levels. Thisis a favorable situation for the appearance of negativeparity vibrations. In fact, low-frequency octupole vibrations have been predicted by random phase approximation (RPA) calculations with the Nilsson potential1) and discovered in several experiments for SD nuclei in Dy and Hg-Pb regions.
One of the central issues concerning the collective
motions of SD nuclei is the octupole instability (appearance of the static shape) depending on angular momentum. Several authors have already demonstrated
the importance of the Coriolis force at low-spin bandhead states of octupole vibrational bands.
Recently, SD bands were discovered in 36,40 Ar, 40 Ca,and 44 Ti. In this mass-number region, we can expect rich experimental information on the collectivemodes of SD nuclei because the observation of rotational bands starting from the 0+ state and the linking
transition between the SD bands and low-lying normal
deformed bands are unique features characterizing theSD states in the region around mass number A ∼ 40(for example, see Ref.2) ).
In this study, we investigate the rotational eﬀect on
the ocutpole vibrations of SD states in the A ∼ 40 region. We have already demonstrated the low-frequency
octupole vibrations of the 0+ SD states through RPAcalculations with the Skyrme force (Skyrme-RPA)3) .
For the excitations from the SD yrast bands, on theother hand, the Skyrme-RPA calculation has not yet
been performed owing to computational limitations.
We develop a new framework of the Skyrme-RPA
calculation. The single-particle Hamiltonian describing independent-particle motion in the triaxially deformed particle–hole potential that is uniformly rotating with rotational frequency ωrot about the x-axis isadopted; h′ = h − ωrot jx . The Skyrme SkM* interaction is employed for the h. The particle–hole residualinteraction is derived from the Skyrme force throughthe Landau–Migdal approximation:stateFig. 1. Isoscalar octupole transition strength for K π = 0−excitation of the SD state in 44 Ti. The results withωrot = 0.0 and 0.6 MeV/h̄ are compared. The deformation is almost constant at (β2 , γ) = (0.58, 9.4◦ ) in bothcases. B(IS3) is shown in Weisskopf units (W.u.).

state

Fig. 2. The same as Fig. 1 but for K π = 1− excitation.

Vph (r, r′ ) = N0−1 [F0 + F0′ τ · τ ′+ (G0 + G′0 τ · τ ′ ) σ · σ ′ ] δ(r − r′ ).

References

The single-particle wave functions φk and the twoparticle wave functions Ψkk′ = φ†k φk′ are represented
by the Fourier-series expansion method in order to ef∗1∗21) T. Nakatsukasa et al.: Phys. Rev. C 53 , 2213 (1996).
2) E. Ideguchi et al.: Prog. Theor. Phys. Suppl. 196, 427(2012).
3) T. Inakura et al.: Nucl. Phys. A768, 61 (2006).

Department of Computer Science and Engineering, University of Aizu
RIKEN Nishina Center- 60 -