Examination of photon strength functions for Dy 162 , 164 from radiative capture of resonance neutrons

The gamma rays following radiative neutron capture on Dy-161,Dy-163 targets were measured with the highly segmented gamma-ray calorimeter Detector for Advanced Neutron Capture Experiments at the Los Alamos Neutron Science Center. The gamma-ray energy spectra for different multiplicities were gathered for tens of s-wave resonances of both possible spins in each nucleus. Analysis of these spectra within the statistical model enabled us to draw conclusions about dipole photon strength functions with emphasis on the scissors mode. The photon strength functions best describing Dy data are very similar to previously published results on even-even Gd isotopes. It was shown that the scissors mode plays a significant role in the decay of highly excited states up to the neutron separation energy. Measurement of multiple resonances allowed us to assess the fluctuations of experimental spectra and to compare the fluctuations with simulated ones. The size of measured fluctuations is on average smaller than predicted from simulations. However, the results are puzzling as the difference between simulations within the statistical model and experiment is not consistent for both nuclei.