Observations of Slow Mesons and Nuclear Disintegrations in Photographic Plates exposed under Carbon Absorbers

The exposure was made at the Jungfraujoch, altitude 3,457 m., using Ilford type C2 nuclear research emulsions. The frequency of stars under thicknesses of carbon up to 220 gm/cm 2 was measured, the experimental value of the absorption length of the radiation causing them being 166±8 gm/cm 2 . The proportion of the stars due to fast π-mesons has been evaluated and, on subtracting this proportion, the absorption length of the radiation responsible for the remainder is found to be 143±10 gm/cm 2 . The energy distribution of the stars having from 3 to 20 tracks is found to be of the form dE/E 2.6 , with no apparent discontinuity. The frequencies of slow π- and π-mesons at various depths is reported. The π-mesons exhibit a transition effect which is interpreted in terms of their production in stars occurring in the carbon absorber. The ratio of negative to positive π-mesons is found to be 3.1 to 1.