Article,
Decay of quadrupole-octupole 1(-) states in Ca-40 and Ce-140
Phys. Rev. C, (March 2016)
DOI: 10.1103/PhysRevC.93.034311
Abstract
Background: Two-phonon excitations originating from the coupling of two
collective one-phonon states are of great interest in nuclear structure
physics. One possibility to generate low-lying E1 excitations is the
coupling of quadrupole and octupole phonons.
Purpose: In this work, the gamma-decay behavior of candidates for the
(2(1)(+) circle times 3(1))(1)-state in the doubly magic nucleus Ca-40
and in the heavier and semimagic nucleus Ce-140 is investigated.
Methods: ((gamma) over bar,gamma') experiments have been carried out at
the High Intensity gamma-ray Source (HI gamma S) facility in combination
with the high-efficiency gamma-ray spectroscopy setup gamma(3)
consisting of HPGe and LaBr3 detectors. The setup enables the
acquisition of gamma-gamma coincidence data and, hence, the detection of
direct decay paths.
Results: In addition to the known ground-state decays, for Ca-40 the
decay into the 3(1) state was observed, while for Ce-140 the direct
decays into the 2(1)(+) and the 0(2)(+) state were detected. The
experimentally deduced transition strengths and excitation energies are
compared to theoretical calculations in the framework of EDF theory plus
QPM approach and systematically analyzed for N = 82 isotones. In
addition, negative parities for two J = 1 states in Ca-44 were deduced
simultaneously.
Conclusions: The experimental findings together with the theoretical
calculations support the two-phonon character of the 1(1)(-) excitation
in the light-to-medium-mass nucleus Ca-40 as well as in the stable
even-even N = 82 nuclei.
