Angular distributions and differential ranges of Ba products from the interactions ofU238with 0.8-400-GeV protons

Abstract

Angular distributions and differential ranges at ${90}^{0}$ to the beam of $^{128}\mathrm{Ba}$, $^{131}\mathrm{Ba}$, $^{135}\mathrm{Ba}^{m}$, and $^{140}\mathrm{Ba}$ emitted in the interaction of $^{238}\mathrm{U}$ with 0.8-400 GeV protons have been measured. The angular distributions of $^{128}\mathrm{Ba}$ and $^{131}\mathrm{Ba}$ change from forward-peaked to sideward-peaked between 3 and 11.5 GeV, while those of $^{135}\mathrm{Ba}^{m}$ and $^{140}\mathrm{Ba}$ are sideward-peaked and independent of bombarding energy in the above regime. Momentum distributions of all products are Gaussian at 0.8 GeV with a mean value increasing from 120 ${(\mathrm{M}\mathrm{e}\mathrm{V}\phantom{\rule{0ex}{0ex}}\mathit{A})}^{1/2}$ for $^{128}\mathrm{Ba}$ to 139 ${(\mathrm{M}\mathrm{e}\mathrm{V}\phantom{\rule{0ex}{0ex}}\mathit{A})}^{1/2}$ for $^{140}\mathrm{Ba}$. The momenta of the neutron-deficient products decrease by nearly a factor of 2 with increasing proton energy and the distributions broaden and become asymmetric. On the other hand, the momentum distributions of $^{135}\mathrm{Ba}^{m}$ and $^{140}\mathrm{Ba}$ are independent of proton energy. The results are analyzed with the two-step model and compared with the kinematics of the coherent interaction model. The implications of the results and comparisons for the reaction mechanism are considered.NUCLEAR REACTIONS $^{238}\mathrm{U}(p,X)^{128}\mathrm{Ba}$, $^{131}\mathrm{Ba}$, $^{135}\mathrm{Ba}^{m}$, $^{140}\mathrm{Ba}$. ${T}_{p}=0.8\ensuremath{-}400$ GeV. Measured angular distributions and differential ranges at 90\ifmmode^\circ\else\textdegree\fi{} to the beam, deduced two-step model parameters.