C12(p, pn)C11Cross Section at 28 Gev

The ${\mathrm{C}}^{12}(p, pn){\mathrm{C}}^{11}$ cross section has been measured in the 28-Gev diffraction scattered proton beam of the Brookhaven AGS. Proton fluxes were determined using nuclear emulsions and the ${\mathrm{C}}^{11}$ activity induced in plastic scintillators was measured by internal scintillation counting. The cross section at 28 Gev is 25.9±1.2 mb, not significantly different from the values at 2 and 3 Gev.