The decay of quadrupole-octupole $1^{-}$ states in ${}^{40}$Ca and ${}^{140}$Ce

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 $(2_1^{+}\otimes 3_1^{-}{)}_{1^{-}}$ state in the doubly-magic nucleus ${}^{40}$Ca and in the heavier and semi-magic nucleus ${}^{140}$Ce is investigated. Methods: $(\vec{\gamma },{\gamma }^{\prime })$ 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 LaBr${}_3$ 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 ${}^{40}$Ca the decay into the $3_1^{-}$ state was observed, while for ${}^{140}$Ce 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 ${}^{44}$Ca 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 ${}^{40}$Ca as well as in the stable even-even $N=82$ nuclei.

arXiv comment11 pages, 6 figures, as accepted in Phys. Rev. C

References in corpus (25)

• Complete electric dipole response and the neutron skin in 208Pb
• Pygmy dipole resonance as a constraint on the neutron skin of heavy nuclei
• Investigation of Pygmy Dipole Resonances in the Tin Region
• Concentration of electric dipole strength below the neutron separation energy in N = 82 nuclei
• Probing the Nuclear Neutron Skin by Low-Energy Dipole Modes
• Low-lying dipole response: isospin character and collectivity in ${}^{68}$Ni, ${}^{132}$Sn and ${}^{208}$Pb
• Information content of the low-energy electric dipole strength: correlation analysis
• Low-energy isovector and isoscalar dipole response in neutron-rich nuclei
• Fragmentation and systematics of the Pygmy Dipole Resonance in the stable N=82 isotones
• On the toroidal nature of the low-energy E1 mode
• Low-energy electric dipole response in 120Sn
• Population of dipole states via isoscalar probes: the splitting of pygmy dipole resonance in ${}^{124}$Sn}
• Level densities and $\gamma$-ray strength functions in Sn isotopes
• The high-efficiency γ-ray spectroscopy setup γ3 at HIγS
• Isospin properties of electric dipole excitations in 48Ca
• Relativistic two-phonon model for low-energy nuclear response
• Origin of Low-Lying Enhanced E1 Strength in Rare-Earth Nuclei
• Pygmy Quadrupole Resonance in Skin Nuclei
• Low-energy electric dipole response of Sn isotopes
• Interrelation between the isoscalar octupole phonon and the proton-neutron mixed-symmetry quadrupole phonon in near spherical nuclei
• Low-energy dipole strength and the critical case of 48Ca
• Two-phonon 1- state in 112Sn observed in resonant photon scattering
• Q-phonon description of low lying 1^- two-phonon states in spherical nuclei
• Lifetime measurement of excited low-spin states via the $(p,p^{\prime }\gamma$) reaction
• Effects of phonon-phonon coupling on properties of pygmy resonance in ${}^{124-132}$Sn

Cited by in corpus (3)

• Shape coexisistence and collective low-spin states in ${}^{112,114}$Sn studied with the $(p,p^{\prime }\gamma )$ DSA coincidence technique
• Influence of complex configurations on properties of pygmy dipole resonance in neutron-rich Ca isotopes
• Direct demonstration of the two-phonon structure of the $J^{\pi }=1_{4742\mathrm{keV}}^{-}$ state of ${}^{88}$Sr