EXPERIMENTAL-OBSERVATION OF LONG DELAY TIMES IN THE REACTION INDUCED BY OXYGEN IONS ON NICKEL CRYSTALS

The crystal blocking technique has been used to measure nuclear time d elays in the O-16(135 MeV)+(nat)Ni reaction. From the axial blocking p atterns 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 found . Two interpretations of these findings have been discussed. The first one seems to indicate that nucleus-nucleus dynamics has to be include d in simple statistical models to understand the time scale of fusion- fission processes. In the second interpretation, an explicit model for dechanneling shows how the blocking technique can be extended to meas ure time delays in decay chains.