Studies of the Recoil Properties of Products of the Interaction ofU238with 11.5-GeV Protons

The thick-target thick-catcher recoil properties of 23 rare-earth nuclides, produced in the interaction of 11.5-GeV protons with uranium, were measured in the mass range 135 to 165. The ratio of the range of a product from multi-GeV protons to that from 450-MeV protons, called the "relative range", was calculated for all nuclides studied in the mass region 82-165. For neutron-excess products, the relative range was around 0.95 and dropped sharply over two $Z$ units to 0.48 for very neutron-deficient products. This relative range behavior was used to analyze isobaric charge dispersion curves into three individual charge dispersion curves corresponding to two fission mechanisms (a low-excitation energy process, fission I, and a high-excitation energy process, fission II) and a nonfission (spallation) mechanism. The fractional isobaric cross section for the spallation process decreases with decreasing mass number from 0.98 at mass 170 to about 0.14 at mass 111 and then increases with decreasing mass number to 0.49 at mass 74. The products are neutron deficient, of low range, and with forward-to-backward recoil ratios (F/B) close to unity. The range values increase almost linearly with $\Delta A$ (mass difference from the target nucleus) from 2.2 ${\mathrm{m}\mathrm{g}/\mathrm{c}\mathrm{m}}^2$ U at $\Delta A$ of 70 to 5.6 ${\mathrm{m}\mathrm{g}/\mathrm{c}\mathrm{m}}^2$ U at $\Delta A$ of 160. The value of $v_{\parallel }$, the velocity imparted to the target nucleus in the beam direction as a result of the intranuclear cascade, decreases from 0.04 ${\mathrm{}(\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{a}\mathrm{m}\mathrm{u})\mathrm{}}^{1/2}$ at $\Delta A$ of 70 to 0.01 ${\mathrm{}(\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{a}\mathrm{m}\mathrm{u})\mathrm{}}^{1/2}$ at $\Delta A$ of 100 and then increases to 0.02 ${\mathrm{}(\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{a}\mathrm{m}\mathrm{u})\mathrm{}}^{1/2}$ at $\Delta A$ of 160. The fractional isobaric cross section for the fission II process is roughly constant with a maximum value of 0.17 for mass number 131. The relative range values for these products are about 0.9 and the F/B values are also close to unity.