Bogoliubov Laboratory of Theoretical Physics

Low-Energy Nuclear Physics Department Seminar

Date and Time: Friday, 15 April 2022, at 2:30 PM

Venue: Blokhinstev Conference Hall (4th floor), Bogoliubov Laboratory of Theoretical Physics; online on Zoom

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Seminar topic: “On decay widths of giant dipole resonances in the lead region”

Speaker: Rashid Nazmitdinov

Abstract:

The description of giant dipole resonance (GDR) decay width requires to trace the spreading of the highly excited, collective one-phonon dipole state along the hierarchy of particle-hole configurations with various degree of complexity. Our microscopic calculations (based on the Skyrme forces) demonstrate that Landau damping of the one-phonon states is the basic mechanism of the decay widths of the GDR in heavy nuclei around ²⁰⁸Pb. On the other hand, the microscopic coupling between the one- and two-phonon components of the wave function (responsible for the spreading width) is quite prominent on the redistribution of the dipole strength, obtained in the one-phonon approximation. We suggest the hybrid model of the decay width, in which the strength function is built on the microscopic one-phonon strength distribution folded with the energy-dependent Lorentzian. By means of the two-phonon density, provided by the modified Fermi gas model with uniformly spaced states, and the weak constant interaction between the one-phonon states and these two-phonon states, we obtain analytically: (i) the energy-dependent smearing parameter; and (ii) the energy-dependent shift of the one-phonon states in this Lorentzian. Estimating the coupling from the Random Matrix Theory approach, we reproduce with a good accuracy the gross structures of the dipole decay widths obtained microscopically.