Charge distribution and recoil properties in the fission of 208Pb by 11·5 GeV protons

Abstract

Cross-sections and thick-target recoil properties have been determined for a number of products in the mass region 100–113 from the interaction of 208Pb with 11·5 GeV protons. The recoil ranges of the neutron deficient products are approximately a factor of two smaller than those of the neutron excessive products are approximately a factor of two smaller than those of result a charge dispersion curve consisting of two gaussians, peaking at N Z = 1·24 and 1·34 , was constructed to fit the measured cross-sections of the A = 111 isobars. The resulting curve is single-peaked but has a pronounced shoulder on the neutron excessive side. The curve for the neutron excessive products is very similar to that obtained in the fission of 208Pb by 450 MeV protons except for a reduction in the value of the integrated cross-section. The values of the average deposition energy, average total kinetic energy of the primary fragments, and average separation distance at scission obtained for these products from their recoil properties are nearly equal to the corresponding values at 450 MeV. Integration of the charge dispersion curve for the neutron deficient products indicates a 82 per cent contribution to the total isobaric cross section at A = 111. Comparison of the properties of the neutron deficient products with similar results previously obtained for a 238U target as well as with evaporation calculations indicates that only a fragmentation mechanism can explain all the experimental results.