Direct observation of first-chance fission of No 258

The multiplicities, angular correlations, and energy spectra of the neutrons associated with fission were measured for the reactions of {sup 25,26}Mg+{sup 232}Th at {sup 25}Mg and {sup 26}Mg projectile energies of 132 and 148 MeV, respectively. From these data, we extracted a value of {gamma}{sub n}/{gamma}{sub f} for the first-chance fission of {sup 258}No at an excitation energy of 61 MeV. The implications of this result for understanding the survival probabilities of excited heavy nuclei formed in ''hot'' fusion reactions are discussed.