ATTENUATION OF PHOTONS AT 3-14-KEV ENERGIES IN HELIUM

We have measured the total photoattenuation cross section of helium for photons in the energy range of 314 keV. At these energies, the photoionization cross section is rapidly decreasing, so that Compton scattering is significant at 4 keV and dominates at the highest energies. Our measurements verify the dominance of Compton scattering in this energy range, and its importance in recent measurements of the ratio of double to single photoionization of helium. The measured cross sections are close to the combined calculated cross sections for Compton scattering and photoionization; we are able to distinguish the contributions of the two effects. © 1995 The American Physical Society.