Energy dependence of GAMMA/sub f//GAMMA/sub n/ for the nucleus $sup 216$Rn

The /sup 209/Bi + /sup 7/Li reaction was used to determine experimentally GAMMA /sub f// GAMMA /sub n/ for the initial compound nucleus / sup 216/Rn. Cross sectio ns for the (/sup 7/Li,f) reaction were measured at bombarding energies between 24 and 34 MeV by detecting coincident fiasion fragments. All the other components of the total reaction cross section are due to (/sup 7/Li,xn), (/sup 7/Li,txn) and (/sup 7/Li, alpha xn) reactions. They wer e determined by observing known energy alpha particles from the short lifetime decays of various Rn, At and Po isotopes. The background due to prompt reaction particles was eliminated by using a pulsed (/sup 7/Li-beam and detecting the decay particles between beam pulses. Correction for the effects of second chance fission was obtained from measurements of cross sections for the (/sup 6/Li,f) and (/sup 6/Li,xn) reactions at approximate energies. The results give a direct measurement of GAMMA /sub f// GAMMA /sub n/ since both fission and neutron evaporation cross sections were determined. The experimental values of GAMMA / sub f// GAMMA /sub n/ for /sup 216/Rn and eariler data fo r /sup 210/Po are analyzed with a J dependent statistical model and the effect of incorporating an enhancement of the level density at the saddle point due to coupling to collective rotations is investigated. Fission barriers extracted with a variety of assumptions about the level densities are compared with theoretical predictions. (auth)