The fission time scale measured with an atomic clock

We present a new direct method of measuring the fission absolute time scale using an atomic clock based on the lifetime of a vacancy in the atomic K-shell. We studied the reaction Ne-20 + Th-232 -> O-16 + U-236* at 30 MeV/u. The excitation energy of about 115 MeV in such a reaction is in the range where a fission lifetime of the order of 10(-18) s has been suggested on basis of blocking experiments. The lifetime of the K-shell hole for U is about 6x10(-18) s. The reaction channel is detected by a forward hodoscope, operated in coincidence with detectors for fission fragments and with Germanium detectors. The latter detectors allow one to detect the characteristic K x rays. The K-shell ionization probability due to the projectile and the projectile-like fragment is about 2%. Depending on the fission lifetime of the U nuclei, either a continuum (short lifetimes) or an explicit characteristic K x-ray spectrum of U (long lifetimes) can be observed. First analysis indicates a x-ray yield in the U energy region.