Proton Spectra from Reactions Induced by 30.5-MeV Alpha Particles

The ($\alpha ,p$) reaction has been studied at 30.5 MeV for the targets ${\mathrm{Al}}^{27}$, ${\mathrm{Ti}}^{48}$, ${\mathrm{V}}^{51}$, Fe, ${\mathrm{Co}}^{59}$, ${\mathrm{Ni}}^{58}$, ${\mathrm{Ni}}^{60}$, ${\mathrm{Ni}}^{61}$, ${\mathrm{Ni}}^{62}$, ${\mathrm{Cu}}^{63}$, ${\mathrm{Cu}}^{65}$, ${\mathrm{Zn}}^{67}$, ${\mathrm{Nb}}^{93}$, Mo, ${\mathrm{Rh}}^{103}$, Pd, ${\mathrm{Cd}}^{113}$, ${\mathrm{Cd}}^{114}$, ${\mathrm{Sn}}^{119}$, ${\mathrm{Sn}}^{120}$, ${\mathrm{Sn}}^{124}$, ${\mathrm{Ta}}^{181}$, ${\mathrm{Pt}}^{195}$, and ${\mathrm{Au}}^{197}$. Proton evaporation spectra were measured at 30, 60, 90, 120, and 150° up to excitation energies of 25 MeV in the residual nucleus. The spectra have been compared with statistical-model predictions and the parameters $a$ and $T$ obtained. The lack of mass dependence of these parameters and the average low value of the level-density parameter $a=5.5\mathrm{}$ ${\mathrm{MeV}}^{-1\mathrm{}}$ add evidence for a nuclear-temperature anomaly. The anomaly is discussed in terms of recent intermediate-resonance models.