Screening effects in pair production by 10-MeV photons on uranium atoms.

Abstract

With a partial-wave interpolation method we calculated the positron energy spectra of pair production in the field of uranium atoms for photons of energy [ital k]=10 MeV, permitting a comparison of theory with the recent experiment. Our results show that the atomic-electron screening effect decreases the cross section for the main region of the positron energy spectra which contributes to the total pair-production cross section, and the effect can be as large as about 9% for the region of low positron energies which contributes little to the total pair-production cross section. The screening effect to the total pair-production cross section is about 3.5%. Our results also indicate that the approximate treatment of screening through energy-shift screening theory becomes inadequate at this intermediate photon energy, while the approximate treatment of screening through form-factor screening theory is quite good. Our result for the total pair-production cross section is compared with the experimental result.