Fission of lead induced by 600 MeV protons

Abstract Absolute radiochemical fission yields have been measured for 12 nuclides of Rb, Ag, Cd and Cs and relative fission yields measured for seven Kr-isotopes and eight Xe-isotopes produced by fission of natural lead induced by 600 MeV protons. The relative Kr- and Xe-yields have been determined using the ISOLDE-facility at CERN. It is suggested that the production rate of a nuclide per m.b. of nuclear reaction cross section should be used as a figure of merit for on-line facilities like Isolde. During the present experiment 3·4 × 10 6 nuclei/sec. m.b. and 2·0 × 10 6 nuclei/sec, m.b. were obtained for Kr- and Xe-isotopes, respectively. Charge and mass distributions and charge dispersion for fission of lead with 600 MeV protons are determined using our measured fission yields and some yields measured by other groups. The most probable charge Z p , for a given mass and the width (FWHM) of the charge dispersion, both increase linearly with mass number. The integrated mass distribution curve gives a fission cross section of 149±6 m.b. Elemental yield distribution is constructed and shows a most probable atomic number of 40·0, giving Mercury as the most probable fissioning element. Assuming no proton evaporation from fission fragments, it is suggested that elemental yield distributions and isotopic yield distributions should be used rather than mass distribution and charge distribution and dispersion for the purpose of obtaining information on the fissioning nuclei. The elemental yield distribution is discussed on the bases of the liquid drop model for fission giving an average nuclear temperature at saddle point of 2·09 MeV, and a total number of neutrons evaporated after fission of about 13. Estimates of most probable cascade residuals for each residual element based on Monte Carlo intranuclear cascade calculations at 380 MeV together with presently observed most probable isotopes for each product Z , are used to predict average cascade deposition energies for events leading to specific products. The agreement with literature values from recoil experiments is good.