The dependence of cosmogenic isotope production on solar modulation and on geomagnetic field intensity has been calculated, and spallation yields based on the Silberberg-Tsao formalism have been determined. The stratospheric inventory of 7Be during the period 1970--1974 has been calculated to be about 4.5mCi, in good agreement with measured values. The calculated radiocarbon reservoir of 1.75 cme-2 s-1 (where results are integrated over the whole earth) is in good agreement with experimental value of 1.8. Geomagnetic and solar effects were taken into account.