DIFFERENTIAL RANGES AND ANGULAR-DISTRIBUTIONS OF BA FRAGMENTS FROM THE INTERACTION OF U-238 WITH 11.5-GEV PROTONS

Angular distributions and differential ranges at 90°to the beam direction have been measured for the following products from the interaction of U238 with 11.5-GeV protons: Ba128, La131, Ba131 (independent), Bam135, and Ba140. All the angular distributions peak at sideward angles. A two-parameter (n ̂> and ba) fit to the angular distributions based on the two-step model yields an anisotropy parameter, ba, of ̂> -0.2 for all products. The value of ̂>v ̂>. the mean forward component of velocity of the struck nuclei, is also insensitive to the composition of the observed products. A sharp transition in the momentum spectra derived from the differential ranges is observed just over one Z unit to the neutron-deficient side of stability. Products on the neutron-rich side of this transition have narrow, symmetric spectra, with mean values of ̂>130 ̂>(MeVA)12, that are characteristic of fission. Products on the neutron deficient side have broad, asymmetric spectra, with a mean value of only ̂>70 ̂>(MeVA)12, as expected for a deep spallation mechanism. The spectrum of independently formed Ba131, which lies in the transition region, was decomposed into fission and deep spallation contributions, with the latter accounting for most of the cross section. NUCLEAR REACTIONS U238(p,x) Ba128, La131, Ba131, Bam135, Ba140, Ep=11.5 GeV; measured angular distributions and differential ranges at 90°; inferred momentum spectra. © 1979 The American Physical Society.