Isobaric yield distribution in fission of uranium by 20-85 MeV protons.

The independant format ion cross-sections of ^139Ba, ^139ce, ^141La , ^141ce, and ^143ce and the cumulative formation cross-sections of ^139Cs, ^141Ba, and ^143La produced in the fission of natural uranium by protons of energies 20-85 MeV have been measured radiochemically. Excitation functions were constructed and the proton energies at which the excitation functions reach their maxima fall on a smooth curve when plotted against neutron-to-proton ratio of the product. Nuclear charge dispersion curves were constructed at 20, 30, 40, 50, 60, 70, 80, and 85 MeV. The general behaviour is similar to that observed by previous workers. With increasing proton energy the curves broaden and the most probable charge approaches the line of beta-stability. These phenomena are qualitatively explained in terms of neutron evaporation. Experimental yields showed good agreement when compared with Wahl's empirical charge distribution curve. It seems that charge dispersion can be very adequately represented in the form of a Gaussian distribution. [...