CRYSTAL BLOCKING - EXPERIMENTAL-EVIDENCE OF LONG DELAY TIMES IN THE REACTION INDUCED ON NICKEL BY OXYGEN IONS

The crystal blocking technique has been used to measure nuclear time d elays in the O-16 (135 MeV) + Ni-nat reaction. From the axial blocking patterns the time delays for the production of fragments with Z from 13 to 18 have been extracted. Times of the order of 10(-18) s for even Z and less than the sensitivity of the method for odd Z have been fou nd. Two interpretations of these findings have been discussed. The fir st one seems to indicate that nucleus-nucleus dynamics has to be inclu ded in simple statistical models to understand the time scale of fusio n-fission processes. In the second interpretation, an explicit model f or dechanneling shows how the blocking technique can be extended to me asure time delays in decay chains.