The production of positive pions by protons on protons has been studied at 00, 350 and 580 to the beam of 341 Mev protons produced by the Berkeley ayncbro-cyclotran. In the collision of two protons, two reactions are possible which lead to a w+_me eon: (1) P + p1+ + D and (2)? + + N +P. The experimental results at 00 show an energy spectrum from 0 to 70 Mev which is farily flat except for a large peak at the high energy end. The flat portion of the spectrum can only be due to reactIon (2). A comparison of the shape of the peak with the results of the phenomenological theory of Brueckner and Watson shows that the peak is due solely to reaction (1). This fact, together with a measurement of the energy of the beam and of the energy of the pions from reaction (1), gives the value 275.1±2. 5 electron masses for the mass of the positive pion. The angular distribution in the center of mass system for reaction (1) as obtained from the data at the above three angles, is 3. 3*1. 2 1.11±. 06 + cos 2 Q]. 10 29 cm2 st erad.-1 and the total cross section for reaction (1) is 1. 8*0. 6 10 28cm2. These results have been compared with the results obtained by Durbin. Loar, and Steinberger and by Clark, Roberts, and Wilson on the inverse reaction, it + D.-P + P. UsIng the theorem of detailed balancing, these experiments lead to the value zero for the spin of the positive pion with good certainty.

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Since the magnetic field is everywhere in phase in the mode used here, N can be defined uniquely as the surface integral of the crest value of the magnetic induction. ** IKS units are used throughout.

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