Isomer Ratio ofCe137m to Ce137gProduced in Several Charged-Particle Reactions

The ${\mathrm{Ce}}^{137m}-{\mathrm{Ce}}^{137g}$ isomer ratio is studied to obtain information on the effect of angular momentum in the de-excitation of a compound nucleus. The ratio of the formation cross section of the high-spin isomer to that of the low-spin isomer is measured as a function of energy for reactions induced by ${\mathrm{He}}^3$, ${\mathrm{He}}^4$, ${\mathrm{Li}}^7$, and ${\mathrm{C}}^{12}$. The ratio is seen to increase with increasing projectile energy and is shown to correspond to an increase in the average angular momentum. The isomer-ratio results are compared with calculations using the Huizenga-Vandenbosch theory. Using the nuclear temperature based on the Fermi-gas model and the spin cutoff factor calculated with 0.5 of the rigid-body moment of inertia, reasonable agreement was obtained with experimental results in all four reactions studied.