One of the striking f e a t u r e s of Dirace s theory of the electron was the appearance of solutions to h i s equations which r e q u i r e d the existence of an antiparticle, l a t e r identified a s the positron.The extension of the Dirac theory to the proton r e q u i r e s the existence of an antiproton, a p a r t i c l e which b e a r s to the proton the same relationship a s the positron to the e l e c t r o n . However, until experimental proof of the existence of the antiproton was obtained, it might be questioned whether a proton i s a D i r a c p a r t i c l e in the s a m e s e n s e a s i s the electron. F o r instance, the anomalous magnetic moment of the proton indicates that the simple Dirac equation does not give a complete description of the proton.The experimental demonstration of the existence of antiprotons was thus one of the objects considered in the planning of the Bevatron. The minimum l a b o r a t o r y kinetic energy for the formation of an antiproton in a nucleon-. nucleon collision is 5. 6 Bev. If the t a r g e t nucleon i s in a nucleus and h a s sorrle momentum the threshold i s lowered. Assuming a F e r m i energy of 25 Mev, one m a y calculate that the threshold for formation of a proton-antiproton p a i r i s approximately 4. 3 Bev. Another, 2 -step, p r o c e s s that h a s been considered by ~e l d m a n ' h a s a n even lower threshold.

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