Statistical giant dipole resonance decay of highly excited states of 63Cu.

Abstract

Continuum \ensuremath{\gamma}-ray spectra from decays of $^{63}\mathrm{Cu}$ formed at initial excitation energies of 22.5 to 77.4 MeV and maximum spin up to 40\ensuremath{\Elzxh}, using $^{4}\mathrm{Co}$, $^{6}$Li${+\mathrm{}}^{57}$Fe, $^{12}$C${+\mathrm{}}^{51}$V, and $^{18}$O${+\mathrm{}}^{45}$Sc entrance channels, have been measured and analyzed. The parameters of the giant dipole resonance strength function have been extracted using a statistical code in a nonlinear least-squares fitting routine. Except for the cases of $^{4}\mathrm{He}$ and $^{6}\mathrm{Li}$ at the highest bombarding energies, which show evidence for nonstatistical effects, spectra are well reproduced by statistical calculations. The mean energy and strength of the giant dipole resonance built on excited states of $^{63}\mathrm{Cu}$ are close to the ground-state values, while the width varies smoothly from \ensuremath{\sim}5 MeV for the ground-state giant dipole resonance up to 10.6\ifmmode\pm\else\textpm\fi{}0.6 MeV in the temperature range up to 1.9 MeV and mean spin in the range 0--23\ensuremath{\Elzxh}. The large range of energies studied permitted different level density formulations to be tested. Measured spectra from $^{6}$Li${+\mathrm{}}^{98}$Mo and $^{6}$Li${+\mathrm{}}^{181}$Ta at ${E}_{\mathrm{lab}{(\mathrm{}}^{6}\mathrm{Li})=36}$ MeV show a strong nonstatistical enhancement at high \ensuremath{\gamma}-ray energies.