Reconstruction of high-energy part of gamma-ray spectrum in thermal neutron capture by $^{113}$Cd

Average gamma-ray spectrum from $^{114}$Cd after thermal neutron capture in $^{113}$Cd was evaluated in units of mb/MeV. Two approaches are considered for estimation of average gamma-ray spectrum with normalization of the experimental data: mean spectra for all gamma-energies were found by averaging frequency polygon for experimental data histogram, and mean spectra were estimated as combination of theoretical values at low gamma-ray energies and averaging experimental data in high-energy range. The experimental spectra were evaluated from the gamma-intensities given by Mheemeed et al [A. Mheemeed et al., Nucl. Phys. A 412 (1984) 113] and Belgya et al [T. Belgya et al., EPJ Web Of Conf. 146 (2017) 05009]. They were normalized to average theoretical spectrum which were calculated by EMPIRE and TALYS codes with default input parameters. Procedure of normalization of high-energy part of the spectrum was described. As for now, the most reliable estimated $gamma$- spectrum for $^{113}$Cd(n,{x$gamma$}) reaction induced by thermal neutrons was presented.

Verification of Models for Calculation of E1 Radiative Strength

Photoabsorption cross sections and gamma-decay strength function are calculated and compared with experimental data to test the existing models of dipole radiative strength functions (RSF) for the middle-weight and heavy atomic nuclei. Simplified version of the modified Lorentzian model are proposed. New tables of giant dipole resonance (GDR) parameters are given. It is shown that the phenomenological closed-form models with asymmetric shape can be used for overall estimates of the dipole RSF in the gamma -ray energy region up to about 20 MeV when GDR parameters are known or the GDR systematics can be adopted. Otherwise, the HFB-QRPA microscopic model and the semi-classical approach with moving surface appear to be more adequate methods to estimate the dipole photoabsorption RSF.

Comparison of Analytical Methods of E1 Strength Calculations in Middle and Heavy Nuclei

Simple analytical models for E1 strength function calculations of the $gamma$-decay are investigated.

Shape of Dipole Radiative Strength Function for Asymmetric Nuclei

The semiclassical method for description of the radiative strength function is used for asymmetric nuclei with $N e Z$. The theory is based on the linearized Vlasov-Landau equations in two-component finite Fermi liquid. The dependence of the shape $E1$ strength on the coupling constant between proton and neutron subsystems was studied.

Dependence of Nuclear Level Density on Vibrational State Damping

The response function approach is proposed to include vibrational state in calculation of level density. The calculations show rather strong dependence of level density on the relaxation times of collective state damping.

Non-Markovian Collision Integral in Fermi-systems

The non-Markovian collision integral is obtained on the base of the Kadanoff-Baym equations for Green functions in a form with allowance for small retardation effects. The collisional relaxation times and damping width of the giant isovector dipole resonances in nuclear matter are calculated. For an infinite Fermi liquid the dependence of the relaxation times on the collective vibration frequency and the temperature corresponds to the Landaus prescription.

Two-body relaxation times in heated nuclei

The retardation and temperature effects in two-body collisions are studied. The collision integral with retardation effects is obtained on the base of the Kadanoff- Baym equations for Green functions in a form with allowance for reaching the local equilibrium system. The collisional relaxation times of collective vibrations are calculated using both the transport approach and doorway state mechanism with hierarchy of particle-hole configurations in heated nuclei. The relaxation times of the kinetic method are rather slowly dependent on multipolarity of the Fermi surface distortion and mode of the collective motion. The dependence of the relaxation times on temperature as well as on frequency of collective vibrations is considered and compared. It is shown that variations of the in-medium two-body cross-sections with energy lead to non-quadratic dependence of the collisional relaxation time both on temperature and on collective motion frequency.

Testing and improvements of gamma-ray strength functions for nuclear model calculations of nuclear data

A closed-form thermodynamic pole approach,TPA, is developed for average description of the E1 radiative strength functions using the microcanonical ensemble for initial states. A semiclassical description of the collective excitation damping in this method is based on modern physical notion on the relaxation processes in Fermi systems.The TPA model gives rather accurate means of simultaneous description of the gamma- decay and photoabsorption strength functions in the medium and heavy nuclei. It is able to cover a relatively wide energy interval, ranging from zeroth gamma-ray energy to values above GDR peak energy, as compared with the others closed-form models for calculation of the E1 strength.

An investigation of interplay between dissipation mechanisms in heated Fermi systems by means of radiative strength functions

A simple analytical expression for the gamma-decay strength function is derived with microcanonical ensemble for initial excited states. The approach leads to both a non-zero limit of the strength function for vanishing gamma-ray energy and a partial breakdown of Brink hypothesis. It is shown that the low energy behaviour of the gamma-decay strength functions is governed by the energy behavior of the damping width. It may provides a new tool for study of the interplay between different relaxation mechanisms of the collective excitations.