Radiative Alpha-Particle Capture inNi58andXe136at Higher Energies

Abstract

The cross sections of the ($\alpha , \gamma$) reaction have been measured as a function of bombarding energy in ${\mathrm{Ni}}^{58}$ and ${\mathrm{Xe}}^{136}$ up to about 35 Mev. In both cases the capture events were identified by means of the specific radioactivity produced in the reaction. In the bombardment of ${\mathrm{Ni}}^{58}$ it was necessary to make use of the tight angular spread of recoils in the capture reaction to distinguish these recoils from those of the ${\mathrm{Ni}}^{60}(\alpha , 2\mathrm{n})$ reaction. Both measured capture cross sections rise to a maximum value (${\mathrm{Ni}}^{58}$: 400 μb, ${\mathrm{Xe}}^{136}$: 60 μb) at an excitation energy of about 20 Mev. A comparison of the observed cross sections with those obtained in ($p, \gamma$) reactions at similar energies suggests that these higher energy capture reactions take place largely through the formation of a compound nucleus rather than by any "direct" mechanism.