Use of Blocking in Crystals to Study the Lifetime for Fission ofU238BY 12-MeV Protons

Abstract
Plastic detectors were used to observe angular distributions of fission fragments emerging from a UO2 single crystal. In fission induced by thermal neutrons and by 12-MeV protons, characteristic blocking patterns were observed, showing strong attenuations along major crystal axes. This shows that fission occurred while the nuclei were within 0.1 Å of a lattice site and indicates that the total lifetime in 12-MeV proton fission is less than 2×1017 sec.