Direct Determination of the Lifetime of Excited Compound Nuclei by Angular Distribution Measurements of Fission Fragments Emitted from Single Crystals

The lifetime for decay of excited ${\mathrm{Np}}^{238}$ compound nuclei has been determined by measuring the emission distribution of fission fragments from a uranium oxide single crystal bombarded with 10-MeV protons. The proton energy, and with this the compound nuclei excitation energies, were selected to give second-chance fission ${\mathrm{Np}}^{238}$ compound nuclei with lifetimes in the range detectable by this technique.