Nuclear Gamma-Absorption Cross Section ofCu63

The absolute intensity of the bremsstrahlung beam from 46-Mev electrons in the Chicago betatron has been determined. Copper foil was irradiated and its activity measured with a calibrated counter. The integrated cross section for ${\mathrm{Cu}}^{63}(\gamma ,n){\mathrm{Cu}}^{62}$ was found to be (0.77±0.15) × ${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$ Mev. A Victoreen thimble, surrounded by a ¼″-thick lead wall and inserted into the beam, measured one r per minute for every 2.5×${10}^7$ Mev ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ of beam intensity.