Charge Dispersion and Recoil Properties atA=131from the Interaction ofU238with 11.5-GeV Protons

Abstract

Independent and cumulative yields have been measured for eight $A=131$ nuclides formed in the interaction of $^{238}\mathrm{U}$ with 11.5-GeV protons. A good fit to the cross sections was obtained with a charge dispersion consisting of two overlapping Gaussians peaking at $Z=52.2 \mathrm{and} 56.5$. The neutron-excessive curve accounts for about 40% of the total isobaric yield of 23.3\ifmmode\pm\else\textpm\fi{}0.4 mb. Thick-target recoil properties were determined for all the nuclides. The recoil ranges are characteristic of fission fragments for $^{131}\mathrm{Sb}$ through $^{131}\mathrm{Cs}$ but decrease by a factor of 2 between $^{131}\mathrm{Cs}$ and $^{131}\mathrm{La}$. This decrease occurs some two $Z$ units beyond the minimum between the two humps in the charge dispersion. The deposition energies derived from the recoil data exhibit a similar trend as the ranges, increasing in the manner expected for fission products up to barium but not beyond. The transformation of isotopic to isobaric yield distributions is considered and it is concluded that the use of $\frac{N}{Z}$ as the composition variable gives the best agreement with experiment.