Fission and gamma-ray decay of the 238U shape isomer

The decay of the 238U superdeformed shape isomer has been reinvestigated by detecting for the first time simultaneously the fission and the gamma-back decay. An electrostatic deflection system has been used to transport the 238mU recoils, produced in a 238U(d, pn) reaction with a pulsed beam of 18 MeV deuterons, in front of a detector set-up consisting of three ion-implanted solid-state detectors and a Ge(Li) gamma-detector. The gamma-back decay has been measured in coincidence with conversion electrons of the 2+→0+ transition deexciting the first rotational state in 238U. Two gamma-transitions of 2.513 MeV and 1.878 MeV have been observed with half-lifes consistent with the result obtained for the decay by delayed fission T1/2=(298±18) ns. (orig.)