Basic parameters of the gamma-decay process and properties of the 174Yb nucleus that manifest themselves in radiative resonance-and thermal-neutron capture

Abstract

An independent analysis of available data on the intensities of primary gamma rays from the capture of ≈2-keV neutrons by a 173Yb nucleus is performed. The distribution of the scatter of these intensities around the average value is approximated in various intervals of energies of primary gamma transitions. An extrapolation of the distributions obtained in this way to zero detection threshold for the intensity of a primary gamma transition makes it possible to estimate, independently of other experimental procedures, the expected number of levels of both parities for spins in the range J = 1–4 and the total possible sum of partial widths with respect to electric and magnetic dipole gamma transitions to levels whose excitation energies extend up to about 4 MeV. The results obtained in this way for the level density and the sum of radiative strength functions confirm the characteristic features of analogous data extracted from the intensities of two-step gamma-ray cascades initiated by radiative thermal-neutron capture by 40 ≤ A ≤ 200 nuclei and also make it possible to assess the sign and magnitude of their systematic uncertainty associated with a very strong dependence of radiative strength functions for cascade gamma transitions on the structure of the excited level, at least for excitation energies below half the neutron binding energy. A comparison with model concepts of the level density reveals that the 174Yb nucleus is in a superfluid states for the bulk of excited levels, at least below 3.5 to 4 MeV.