A series of scientific papers “Method of separable approximation for Skyrme force and effects of complex configurations in the structure of exotic nuclei” received the JINR Encouraging Prize for 2021. The works of the series were written by an international group of scientists, including three authors from the nuclei structure sector of the Bogoliubov Laboratory of Theoretical Physics JINR Nikolay Arsenyev, Viktor Voronov, and Alexey Severyukhin.

The study of the properties of medium-heavy and heavy nuclei far from the stability line requires the development of new theoretical approaches. In the series of works, making use of the energy density functional authors suggest a new method allowing to the separable form of the Hamiltonian. The method enables one to perform the calculations in very large configurational spaces.

The generalised equations of the quasiparticle-phonon model have been applied to the study of low-energy spectra of neutron-rich nuclei, in particular, the mixed-symmetry states. The self-consistency condition in the particle-particle channel gave an opportunity to study the role of the surface interaction for the g-factor description in the case of the 2⁺ states. The influence of complex configurations on the characteristics of giant and pygmy resonances was investigated. Anharmonic effects weakly affect the width of the giant dipole resonance (GDR). This effect is crucial for describing the width in the case of the isoscalar giant monopole and quadrupole resonances.

The inclusion of two-phonon configurations gives a considerable contribution to low-energy E1 strength and an essential increasing of the pygmy dipole resonance width of neutron-rich nuclei. Authors have studied for the first time the properties of the double-γ decay of the lowest quadrupole state. It is shown that the γγ-decay width is sensitive to the mixing of the simple and complex configurations. The one-phonon GDR configuration and the two-phonon configuration [GDR ⊗ 2₁⁺] play a key role in the width calculation. The generalised electric dipole polarizability is discussed as a new observable.

References

1. Van Giai Nguyen, Stoyanov Ch., Voronov V. V. Finite rank approximation for random phase approximation calculations with Skyrme interactions: An application to Ar isotopes. // Phys. Rev. C. — 1998. — Vol. 57. — P. 1204–1209.
2. Severyukhin A. P., Stoyanov Ch., Voronov V. V., Van Giai Nguyen Quasiparticle random phase approximation with finite rank approximation for Skyrme interactions. // Phys. Rev. C. — 2002. — Vol. 66. — P. 034304-1–7.
3. Severyukhin A. P., Voronov V. V., Stoyanov Ch., Van Giai Nguyen Separabelized Skyrme interactions and quasiparticle RPA. // Ядерная физика. — 2003. — Т. 66. — № 8. — С. 1480 – 1484
4. Severyukhin A. P., Stoyanov Ch., Voronov V. V., Van Giai Nguyen Nuclear structure calculations with a separable approximation for Skyrme interactions. // Nucl. Phys. A. — 2003. — Vol. 722. — P. 123c – 128c.
5. Severyukhin A. P., Voronov V. V., Van Giai Nguyen Effects of phonon-phonon coupling on low-lying states in neutron-rich Sn isotopes. // Eur. Phys. J. A. — 2004. — Vol. 22. — P. 397 – 403.
6. Severyukhin A. P., Voronov V. V., Van Giai Nguyen Effects of the particle-particle channel on properties of low-lying vibrational states. // Phys. Rev. C. — 2008. — Vol. 77. — P. 024322-1–8.
7. Severyukhin A. P., Voronov V. V., Van Giai Nguyen Description of low-lying state structures with Skyrme interaction. // Ядерная физика. — 2009. — Т. 72. — № 10. — С. 1791 – 1796.
8. Северюхин А. П., Арсеньев Н. Н., Воронов В. В., Ван Джай Нгуен “Исследование структуры ядра с сепарабелизованным взаимодействием Скирма”. // Ядерная физика. — 2009. — Т. 72. — № 7. — С. 1195 – 1199.
9. Lo Iudice N., Stoyanov Ch., Pietralla N. Splitting of the 2⁺ mixed symmetry mode in the proximity of the N = 82 shell closure. // Phys. Rev. C. — 2009. — Vol. 80. — P. 024311-1–7.
10. Severyukhin A. P., Arsenyev N. N., Pietralla N. Proton-neutron symmetry in ⁹²Zr, ⁹⁴Mo with Skyrme interactions in a separable approximation. // Phys. Rev. C. — 2012. — Vol. 86. — P. 024311-1–8.
11. Severyukhin A. P., Arsenyev N. N., Pietralla N., Werner V. Impact of variational space on M1 transitions between first and second quadrupole excitations in ^132,134,136Te. // Phys. Rev. C. — 2014. — Vol. 90. — P. 011306(R)-1–5.
12. Arsenyev N. N., Severyukhin A. P., Voronov V. V., Van Giai Nguyen Influence of complex configurations on properties of the pygmy dipole resonance in neutron-rich Ca isotopes. // Phys. Rev. C. — 2017. — Vol. 95. — P. 054312-1–10.
13. Severyukhin A. P., Arsenyev N. N., Pietralla N., Werner V. Proton-neutron structure of first and second quadrupole excitations of ⁹⁰Sr. // Eur. Phys. J. A. — 2018. — Vol. 54. — P. 4-1–8.
14. Arsenyev N. N., Severyukhin A. P., Voronov V. V., Van Giai Nguyen Low-energy E1 strength distributions of ⁶⁸Ni.// Phys. Part. Nucl. — 2019. — Vol. 50. — № 5. — P. 528–531.
15. Arsenyev N. N., Severyukhin A. P. Origin of low- and high-energy monopole collectivity in ¹³²Sn. // Universe. — 2021. — Vol. 7. — № 5. — P. 145-1–13.
16. Severyukhin A. P., Arsenyev N. N., Pietralla N. First calculation of the γγ-decay width of a nuclear 2₁⁺ state: the case of ⁴⁸Ca. // Phys. Rev. C. — 2021. — Vol. 104. — P. 024310-1–6.