Dipole strength in Se-78 below the neutron separation energy from a combined analysis of Se-77(n, gamma)and Se-78(gamma, gamma ') experiments
Abstract
The dipole strength function and the nuclear level density of the compound nucleus Se-78 were studied in a combined analysis of a cold neutron capture experiment on Se-77 performed at the research reactor in Budapest and a photon-scattering experiment on Se-78 performed at the electron linear accelerator ELBE with bremsstrahlung produced at a kinetic electron energy of 11.5 MeV. In the combined analysis we developed the extreme statistical code gamma DEX for the simulation of radiative cascade deexcitations occurring in neutron capture and photon scattering.
Comparisons of experimental and simulated neutron capture spectra allow us to estimate a temperature of T = 900 keV for the level density according to the constant-temperature model for Se-78. Using gamma DEX, we were also able to estimate ground-state branching ratios and intensities of inelastic transitions for states in Se-78 excited via photon scattering.
In this way, we derived the photoabsorption cross section from 4 MeV up to the neutron separation energy from the measured photon-scattering data. The results obtained match the photoabsorption cross section derived from (gamma, n) measurements and show an enhancement of dipole strength around 9 MeV.