Positive mesons produced by 380 Mev alpha-particles in the 184-inch Berkeley cyclotron have been detected by means of photographic plates. The experimental arrangement is similar to that used for detecting negative mesons except that the plates are placed in a position to receive positive instead of negative particles from the target. Heavy positive mesons are observed to decay into secondary mesons in the manner described by Lattes, Occhialini and Powell. Relative numbers of positive aid negative me sons coming from a target are found by placing plates symmetrically on opposite sides of the target. Preliminary results indicate that for a 1/16 inch carbon target there are about one fourth as many heavy positive mesons as heavy negative ones for meson energies of 2-3 Mev in the laboratory system.

Positive mesons produced by 380 Mev alpha-particles in the 184-inch Berkeley cyclotron have been detected by means of photographic plates. The experimental arrangement is similar to that used for detecting negative mesons except that the plates are placed in a position to receive positive instead of negative particles from the target. Heavy positive mesons are observed to decay into secondary mesons in the manner described by Lattes, Occhialini and Powell. Relative numbers of positive aid negative me sons coming from a target are found by placing plates symmetrically on opposite sides of the target. Preliminary results indicate that for a 1/16 inch carbon target there are about one fourth as many heavy positive mesons as heavy negative ones for meson energies of 2-3 Mev in the laboratory system.

The authors have observed traks which they believe to be due to mesons in photographic plates placed near a ta5rget bombarded by 380 Mev alpha particles. The plates used were Ilford Nuclear Research Plates, type C.2. the identification of the particles responsible for the tracks was first made on the basis of the appearance of the tracks; they show the same type of scattering and variation of grain density with residual range found in cosmic ray meson tracks and about two-thirds of them produce observable stars at the end of their range. For a 10-minute exposure in the cyclotron, about 50 meson tracks are found along the 3-inch edge of a photographic plate. Carbon, beryllium, copper, and uranium have been used so far as target materials, and all are found to give mesons. When a carbon target was bombarded with 300 Mev alpha particles, mesons were found but with reduced yield.

Consists of AECD 1-2023 (no. 1-1779 called MDDC).