Observation of a constant average angular momentum for fusion at sub-barrier energies.

Abstract

The cross sections for the fusion reaction $^{128}\mathrm{Te}(^{12}\mathrm{C}, 3n)^{137}\mathrm{Ce}$ were measured from ${E}_{\mathrm{c}.\mathrm{m}.}=34.5 \mathrm{to} 50$ MeV by observing the decay of the ground (${J}^{\ensuremath{\pi}}={\frac{3}{2}}^{+}$, ${t}_{\frac{1}{2}}=9.0$ h) and isomeric (${\frac{11}{2}}^{\ensuremath{-}}$, 34.4 h) states in $^{137}\mathrm{Ce}$. The isomer ratio decreases rapidly from a value of \ensuremath{\simeq}34 at 47 MeV to an essentially constant value of \ensuremath{\simeq}1.5 below 38 MeV. This confirms the prediction of an approximately constant value for the average angular momentum for fusion of heavy ions at energies well below the fusion barrier.