Neutron Spectrum Formation under Neutron Pumping of the Active Medium Formed by Two Stable Gadolinium Isotopes

Due to the possibility of neutron pumping of the active medium formed by Gd¹⁵⁵ and Gd¹⁵⁶ gadolinium isotopes, neutron spectral parameters in the active medium are numerically and theoretically studied. The active medium is placed in a tungsten cylindrical volume. Several versions of a tungsten bulb filled with compact gadolinium oxide with graphite reflectors and without reflectors are considered. It is found that the neutron spectrum in the active medium makes possible population inversion of excitation levels of Gd¹⁵⁶ isotope nuclei at certain combinations of geometrical parameters of the cylindrical volume.