13th APCTP - BLTP JINR Joint Workshop "Modern Problems in Nuclear and Elementary Particle Physics"

Pygmy and giant dipole resonances in 48,50Ca and 68,70Ni

17 Jul 2019, 15:00

20m

International Conference Hall, Dubna, Russia

Modern problems in nuclear and elementary particle physics

Speaker

Dr Nikolay Arsenyev (Bogoliubov Laboratory of Theoretical Physics, JINR, Dubna, Russia)

Description

The structure of exotic neutron-rich nuclei is one of the main science drivers in contemporary nuclear physics research. An attention has been devoted to effects of varying the ratio between the proton $Z$ and neutron $N$ numbers on different nuclear structure characteristics of nuclei deviated from their valley of $\beta$-stability. One of the phenomena associated with the change in $N/Z$ ratios is the pygmy dipole resonance (PDR) [1]. One of the successful tools for describing the PDR is the quasiparticle random phase approximation (QRPA) with the self-consistent mean-field derived from Skyrme energy density functionals (EDF) [2]. Such an approach can describe the properties of the low-lying states reasonably well by using existing Skyrme interactions. Due to the anharmonicity of the vibrations there is a coupling between one-phonon and more complex states [3]. The main difficulty is that the complexity of calculations beyond standard QRPA increases rapidly with the size of the configuration space, and one has to work within limited spaces. Using a finite rank separable approximation for the residual particle-hole interaction derived from the Skyrme forces one can overcome this numerical problem [4-6]. In the present report, we analyze the effects of phonon-phonon coupling (PPC) on the $E1$ strength distributions of neutron-rich calcium and nickel isotopes. Using the same set of the EDF parameters we describe available experimental data for ${}^{48}$Ca, ${}^{68}$Ni and give prediction for ${}^{50}$Ca, ${}^{70}$Ni. The inclusion of the PPC results in the formation of low energy $1^{-}$ states of ${}^{48}$Ca. There is an impact of the PPC effect on low-energy $E1$ strength of ${}^{48}$Ca [7]. The effect of the low-energy $E1$ strength on the electric dipole polarizability is discussed. We predict a strong increase of the summed $E1$ strength below 10 MeV (12 MeV), with increasing neutron number from ${}^{48}$Ca (${}^{68}$Ni) till ${}^{50}$Ca (${}^{70}$Ni) [8]. This work is partly supported by CNRS-RFBR agreement No. 16-52-150003. 1. D. Savran, T. Aumann, A. Zilges // Prog. Part. Nucl. Phys. 2013. V. 70. P. 210. 2. N. Paar, D. Vretenar, E. Khan, G. Colò // Rep. Prog. Phys. 2007. V. 70. P. 691. 3. V.G. Soloviev // Theory of Atomic Nuclei: Quasiparticles and Phonons. 1992. Bristol/Philadelphia. 4. Nguyen Van Giai, Ch. Stoyanov, V.V. Voronov // Phys. Rev. C. 1998. V. 57. P. 1204. 5. A.P. Severyukhin, V.V. Voronov, Nguyen Van Giai // Phys. Rev. C. 2008. V. 77. P. 024322. 6. A.P. Severyukhin, V.V. Voronov, Nguyen Van Giai // Eur. Phys. J. A. 2004. V. 22. P. 397. 7. N.N. Arsenyev, A.P. Severyukhin, V.V. Voronov, Nguyen Van Giai // Phys. Rev. C. 2017. V. 95. P. 054312. 8. N.N. Arsenyev, A.P. Severyukhin, V.V. Voronov, Nguyen Van Giai // in preparation.

Presentation materials

Slides

Arsenyev.pdf