Measurement of compound nuclear lifetimes by the crystal blocking technique

Abstract

The crystal blocking technique has been used to measure the lifetime of the 12.44 MeV 2 + level in 28Si excited in the 27Al(p, α) 24Mg resonance reaction at E p = 885 keV. Both 〈110〉 axial and {111} planar blocking effects in Al single crystals have been investigated. Measurements have been made for two reaction depths, 1000 and 4000 A. Various methods of extracting the lifetime, involving both analytical calculations and computer simulation, are compared. The theoretical change in volume of an axial blocking dip due to a lifetime effect has been calculated in the continuum approximation. The results obtained from the different methods of analysis agree, the average value of the lifetime being 28 as. Although the results show no systematic dependence on reaction depth, pronounced depth effects are evident in computer simulations of the planar blocking dips.