Neutron pumping of active medium formed by gadolinium isotopes Gd155 and Gd156 pair

The possibility of accumulation of excess energy in the active medium formed by the gadolinium isotopes Gd-155 and Gd-156 possible due to the formation and accumulation of Gd-156m nuclei in the isomeric state during radiation capture of neutrons by the nuclei of a stable isotope with a lower mass is shown. A numerical simulation of the dynamics of the energy levels population of Gd-156 nuclei at repetitively-pulsed pumping of the active medium formed by isotope-modified gadolinium oxide was carried out. The calculation for various combinations of neutron duty cycle of pulses, flux density, and neutron energy spectrum in pulses was performed. It was established that combinations of these parameters, which provide the possibility of inverting the population of the excitation levels of Gd-156 isotope nuclei were largely determined by the energy neutron flux spectrum in pulses. •The possibility of accumulation of excess energy in the active medium composed of Gd at the neutron pumping are reviewed.•The results of modeling the dynamics of the energy levels population of nuclei at repetitively-pulsed pumping are presented.•The channel of nucleus formation in the isomeric state as a daughter nucleus is taken into account for the first time.•The results of this study allow to technologically implement the concept of a nuclear-pumped laser.•A variant of creating an active medium based on sintered ceramics of Gd2O3 enriched with the 155th isotope is proposed.