LEVEL DENSITY OF DEFORMED RARE-EARTH NUCLEI

The energy spectra of neutrons inelastically scattered at 90° by 15 elements between In and Bi have been measured for incident neutron energies 5.0, 6.0 and 7.0 MeV using time-of-flight techniques. The energy dependence of the level density has been obtained for each element, and the data are fitted quite well by the independent-particle model w(U) ∝ U-2exp 2(aU) 1 2, although nuclei near shell closures are better described by a constant nuclear temperature. The level density parameters a obtained are in agreement with theoretical expectations, but are significantly lower than those obtained from slow neutron resonance spacings for the deformed nuclei studied, although reasonable agreement is obtained for nuclei outside the deformed region. This conflict is resolved if a modification to the independent-particle model proposed by Ericson is adopted to explain the close resonance spacings observed in the deformed nuclei. © 1968.