Axial radioactivity distributions in 60Co source pencils were measured with a lead collimator and a cavity ionization chamber. Axial γ-ray intensity distributions in the irradiation canister sorrounded by the pencils were measured with a dosimeter consisting of a silicon diode and a charge integrator. The latter distributions well agreed with those calculated from the former distributions by assuming the linear source model. The optimum radioactivity distributions for some arrangement diameters were searched from a point of view of the homogeneity in γ-ray intensity.