Two Topics in Pion Physics. [Part] 1. Photoproduction of Neutral Pions From Complex Nuclei and the Pair-Correlation Function. [Part] 2. The Relative Rate of Absorption of Negative Pions in Hydrogen and Deuterium

A simple theory of the photoproduction of pi /sup 0/ mesons from complex nuclei based on the impulse and closure approximation is studied. The theory is compared with an experiment of Goodwin, Anderson, and Kenney that shows the dependence of the number of decay gammas from pi /sup 0/ mesons photo- produced from various nuclei as a function of the atomic number at 45, 90, and 135 degrees for incident photon energies from threshold to 350 Mev. The dependence measured near threshold and at 45 degrees does not agree with the simple theory nor is it consistent with partial elastic production. By a method of Placzek and Wick the corrections to the simple theory are estimated, and found to be large near threshold. These corrections may explain the discrepancy between the theory and the experimental results. No information about the nuclear-pair correlation function is obtained. The impulse approximation is used to calculate the relative ratio of the radiative absorption rate of pi /sup -/ mesons absorbed in hydrogen and deuterium from an atomic s state. The calculated value of the ratio T = R( pi /sup -/ + d yields 2n + gamma )/R( pi /sup -/ + p yields n + gamma ) is 0.83 plus or minus 0.08. The experimental value is 0.41 plus or minus 0.06. The closure approximation is used to evaluate T. By a method due to Placzek the error due to the closure approximation is shown to be small. (auth