Gamma‐Ray Measurements by the Magnetic Analysis of Compton Electrons

A magnetic spectrometer has been constructed which can be used to determine photon intensities and energies over an energy range of approximately 0.2 to 12 Mev. Over this energy range, the detection efficiency of the spectrometer is such that a monoenergetic photon flux density of the order of 105 photons per cm2 will produce one count. The instrument measures the momentum distribution of Compton electrons ejected from a thin beryllium foil into a small solid angle in the direction of the incident photon beam. A method of converting these measurements to corresponding photon intensities and energies is presented. The calculations necessary to convert to photon intensities are based on the Klein‐Nishina formula, and include the effects of scattering and energy loss of the electrons in the foil. The spectrometer was calibrated from (a) the line shapes produced when the gamma‐rays from the radioactive sources Cs137 (0.661 Mev) and Na24 (1.37 Mev, 2.76 Mev) were incident on the foil, and (b) the intensity measurements of these sources, obtained with an ionization chamber.