Proton-Proton Interactions at 810 Mev

244 examples of proton-proton scattering have been observed by using the hydrogen-filled diffusion cloud chamber of the Brookhaven cloud chamber group. The mean energy of the incident protons was measured to be 810±100 Mev. The reactions observed were (1) $p+p\to p+p$, 126 examples, (2) $p+p\to p+n+{\pi }^{+}$, 84 examples, (3) $p+p\to d+{\pi }^{+}$, 1 example, and (4) $p+p\to p+p+{\pi }^0$, 5 examples, with 28 examples which can be either reaction (2) or (4). The total proton-proton cross section was determined to be 45±6 mb. The ratio $R$ of the cross section for ${\pi }^{+}$ production to that for ${\pi }^0$ production is 17±8. An elastic differential distribution strongly peaked in the forward direction was obtained. Angle and momentum distributions of particles and angular correlations between pairs of particles from reaction (2) are presented. No interactions leading to the production of more than one meson or of heavy unstable particles were identified.