Ⅱ-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 47 (2014)

RIKEN Accel. Prog. Rep. 00 (0)Shape evolution of giant resonances in Nd and Sm isotopes †K. Yoshida∗1 and T. Nakatsukasa∗2A giant resonance (GR) is a typical high-frequency
collective mode of excitation in nuclei. Eﬀects of nuclear deformation on GRs have been investigated bothexperimentally and theoretically. Among them, thedeformation splitting of the isovector giant dipole resonance (GDR), due to diﬀerent frequencies of oscillations along the major and minor axes, is well established. Emergence of a double-peak structure of
the photoabsorption cross section of 150 Nd and 152 Sm
clearly indicates the onset of the deformation in theground state. For the GRs with higher multipolarity, although deformation splitting is less pronounced,
peak broadening has been observed. The detailed andsystematic investigations of GRs would give us uniqueinformation on the shape transition in nuclei.
In contrast to low-energy modes of excitation, GRs
substantially reﬂect bulk nuclear properties. Thus,
their studies may provide information on nuclear matter. Although various macroscopic models have been
applied to GRs, a quantitative description of GRs requires a microscopic treatment of nuclear response.
For heavy deformed open-shell nuclei, the leading theory currently for this purpose is the quasiparticlerandom-phase approximation (QRPA) based on thenuclear energy-density-functional (EDF) method. The
QRPA based on the deformed ground-state conﬁguration with superﬂuidity can treat a variety of excitationsin the linear regime.
We develop a new calculation code of the deformed
HFB and QRPA for use in the massively parallel computers to examine the applicability of the SkyrmeEDF-based QRPA to the excitation modes in heavy
deformed systems. Using this new parallelized code,
the deformation eﬀects on the GRs in Nd and Sm isotopes are investigated. We perform numerical analysis for GRs with a multipolarity L = 0 − 3 with bothisoscalar (IS) and isovector (IV) characters, and examine the incompressibility and the eﬀective mass bothin spherical and deformed nuclei.
Figure 1 shows the strength distributions of IS
monopole and quadrupole excitations in the Sm isotopes. We discuss ﬁrst the giant quadrupole resonance(GQR). With an increase in the mass number, the peakenergy of the ISGQR becomes smaller. This is consistent with the experiment on the systematic observation1),2) . The K splitting, EK=2 − EK=0 , for theISGQR is 2.8 MeV in 154 Sm. This is consistent withthe experimental observation. Since the energy split†∗1∗2Fig. 1. Strength distributions (shifted) of (a) ISGMR and(b) ISGQR in Sm isotopes.

ting associated with deformation is comparable to thesmearing parameter of 2 MeV, the deformation splitting, which is clearly visible in the photoabsorption
cross sections does not appear in the ISGQR.
Next, let us discuss the giant monopole resonance(GMR). In the spherical nuclei, we can see a sharp
peak at around 15 MeV which is identiﬁed as the ISGMR. The ISGMR in deformed nuclei has a doublepeak structure. The higher-energy peak of the IS
monopole strength is identiﬁed as a primal ISGMR
and the lower-energy peak is associated with the coupling to the K π = 0+ component of the ISGQR. Thelower peak of the ISGMR around 11 MeV is locatedat the peak position of the K π = 0+ component of theISGQR.
For the ISGMR in 154 Sm, the SkM* functional gives
the excitation energy, which is very close to the observed value1) . However, in 144 Sm, the SkM* underestimates the observation, and the SLy4 gives the reasonable energy. The present calculation suggests that thenuclear-matter incompressibility corresponds to about
230 MeV, as deduced from the comparison of the GMR
excitation energy for 144 Sm, and 210 MeV for 154 Sm.
References1) M. Itoh et al.: Phys. Rev. C 68, 064602 (2003).
2) D. H. Youngblood et al.: Phys. Rev. C 69, 034315(2004).

Condensed from the article in Phys. Rev. C. 88, 034309(2013)
Graduate School of Science and Technology, Niigata University
RIKEN Nishina Center- 51 -1