ABSOLUTE PAIR PRODUCTION CROSS SECTION OF LEAD AT 2.76 MEV.

Abstract
A value has been obtained for the absolute pair production cross section of lead for the 2.76 Mev. gamma rays of Na24. A collimated beam of these gamma rays was made to fall on a specially constructed target and the positrons produced in the target were detected by counting two-quanta annihilation events by means of two scintillation spectrometers in coincidence. The strength of the Na24 source was measured by a coincidence counting technique and the counter detection efficiency for annihilation radiation was measured with a calibrated Na22 source. The effect of absorption of the 0.511 Mev. annihilation radiation in the target was measured in a separate experiment. The value obtained for the cross section was 2.38 ± 0.62 barns.

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