Experimental observation of long delay times in the reaction induced by oxygen ions on nickel crystals

Abstract

The crystal blocking technique has been used to measure nuclear time delays in the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(135 MeV)${+}^{\mathrm{nat}}$Ni 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 ${10}^{\mathrm{-}18}$ 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 included 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 measure time delays in decay chains.