Statistical gamma decay of the giant dipole resonance in highly excited 46Ti and 52Cr.

Abstract

We have measured inclusive \ensuremath{\gamma}-ray spectra from the reactions \ensuremath{\alpha}${+}^{48}$Ti${\ensuremath{\rightarrow}}^{52}$Cr and $^{19}\mathrm{F}$${+}^{27}$Al${\ensuremath{\rightarrow}}^{46}$Ti, populating final states at moderate temperature and spin. These spectra were analyzed using a statistical model including giant resonance strength functions in the \ensuremath{\gamma}-decay width. The parameters of the giant dipole resonance (GDR) strength function were varied to fit the data. Two different level-density formulations were utilized---one (P\uhlhofer) in which the level-density parameters were adjusted to obtain the best overall fit to the data, and the other (Reisdorf) which contained no free parameters. While the magnitudes of the extracted GDR parameters differed in the two cases, their dependence on final-state energy was similar. The GDR energy was observed to be nearly constant with the final-state energy, and the GDR strength exhausted nearly a full E1 sum rule. In the \ensuremath{\alpha}${+}^{48}$Ti reaction, the GDR width was observed to increase slightly with increasing bombarding energy. In the $^{19}\mathrm{F}$${+}^{27}$Al reaction, a pronounced GDR width increase was observed with increasing bombarding energy and was attributed to an increase in compound nucleus spin. These results are consistent with current calculations based on the rotating liquid-drop model and with recent experimental reports.