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The proton-proton differential scattering cross section has been measured at 105 Mev and at 75 Mev by using the internal beam of the Harvard cyclotron. Scintillation counters detected the scattered and recoil protons in coincidence while the beam current was monitored by measuring the absolute activity of C^11 formed in the polyethylene scattering foil. The cross section as a function of angle in the center-of-mass system appears to be isotropic within statistical deviation. It has the values 5. 410^-27 cm^2 and 6. 610^-27 cm^2 at 105 Mev and 75 Mev respectively, with an estimated error of twenty percent.
Birge et al. (Sun,) studied this question.