Statistical properties of excited nuclei in the mass range 47 ≤ A ≤ 59

摘要

Level densities and their energy dependences for nuclei in the mass range of 47 ≤ A ≤ 59 were determined from the results obtained by measuring neutron-evaporation spectra in respective (p, n) reactions. The spectra of neutrons originating from the (p, n) reactions on (47)~Ti, (48)~Ti, (49)~Ti, (53)~Cr, (54)~Cr, (57)~Fe, and (59)~Co nuclei were measured in the proton-energy range of 7-11 MeV. These measurements were performed with the aid of a fast-neutron spectrometer by the time-of-flight method over the base of the EGP-15 pulsed tandem accelerator installed at the Institute for Physics and Power Engineering (Obninsk, Russia). A high resolution of the spectrometer and its stability in the time of flight made it possible to identify reliably discrete low-lying levels along with the continuum part of neutron spectra. Our measured data were analyzed within the statistical equilibrium and preequilibrium models of nuclear reactions. The respective calculations were performed with the aid of the Hauser-Feshbach formalismof statistical theory supplemented with the generalized model of a superfluid nucleus, the back-shifted Fermi gas model, and the Gilbert-Cameron composite formula for nuclear level densities. Nuclear level densities for (47)~V, (48)~V, (49)~V, (53)~Mn, (54)~Mn, (57)~Co, and (59)~Ni and their energy dependences were determined. The results are discussed and compared with available experimental data and with recommendations of model-based systematics.