Properties of the 158Gd compound state gamma-decay cascades

Photon spectra from thermal neutron capture in natural gadolinium were measured, using the technique of summed amplitudes of coinciding pulses, to study the compound state decay in the 158Gd nucleus and to reveal its main peculiarities. The two-step cascades leading to the first three levels of the rotational band Kπ = 0+ based on the ground state are reported, and differences from previously published data are noted. Decay modes for many levels up to the excitation energy of ≅ 4 MeV are established for the first time. Experimental cascade intensity distributions as a function of the primary transition energy are compared with calculations using different model predictions for level density. Conclusions about the γ-decay characteristics of complex nuclei, which form the beginning of the region of the 4s-maximum neutron resonance strength function, are drawn. (author)