Determination of the Energy Distribution of Bremsstrahlung from 19.5-Mev Electrons

Abstract

The conventional target of a 22-Mev betatron has been replaced by a 0.005-in. platinum target and the intensity spectrum of x-rays produced in the platinum by betatron-accelerated electrons has been measured. The kinetic energy of the monoenergetic electrons at the time of expansion was 19.5 Mev. The x-rays were collimated and observed in the forward direction by studying the electron-positron pairs produced in a cloud chamber filled with air. About 1300 pairs were measured. The intensity spectrum of x-rays is calculated from the pair energy distribution and is compared with the bremsstrahlung theory of Bethe and Heitler. The experimental intensity in the region of 10 Mev is found to be higher than the theoretical value by an amount which is larger than the statistical uncertainty of the experiment. Some details of the pair production process are given, and methods of correcting for instrumental discrimination are discussed and applied.