The Absorption of High Energy Quanta. I.

Abstract

The absorption of quanta between 11 and 20 Mev has been measured with the x-rays from the 22-Mev betatron as a source. The high energy tip of the x-ray spectrum has been isolated for these measurements by using a threshold detector method. The detectors used were copper, iron, and carbon, with which absorption coefficient values were obtained at 11.04, 13.73, and 19.10 Mev, respectively. Aluminum, iron, copper, and lead were used as absorbers. The observed absorption coefficients are in good agreement with existing theory except in the case of lead. The absorption in lead is smaller than predicted. This is probably due to the failure of the Born approximation in the calculation of the pair-production cross section.