Internal-source method of measuring absolute pair-production cross sections

The history, detailed description and results obtained using a unique but simple method of measuring absolute pair-production cross sections is reviewed. These activities which occurred between 1973 and 1985 yielded results for photons on targets of Z=26,29,50,82, and 92 for photons with energies of 1.1205,1.3325,1.8362, and 2.6145MeV. They were measured for these energies and for 1.077MeV for targets up to Z=82. The cross sections deviated significantly from theoretical calculations for energies near threshold. The discrepancy was later confirmed and an explanation suggested.