The Absorption of High Energy Electrons

Author: Neddermeyer, Seth Henry

Year: 1935

Degree: Dissertation (Ph.D.)

Advisors: Millikan, Robert Andrews; Anderson, Carl D.

Committee Member: Unknown, Unknown

Option: Physics

DOI: 10.7907/1fva-rs09

Abstract

A study of about 10,000 photographs of cosmic ray electron tracks, taken by means or the counter controlled cloud chamber -magnet apparatus, has been made with the purpose of observing the interaction of these high energy particle with atomic nuclei and their external electrons. Four main types of interaction are known to occur, viz. (1) Ionization and excitation of atoms. (2) Large energy transfers to extranuclear electrons. (3) Production of positron-negatron pairs. (4) Radiation, presumably in nuclear encounters. Data obtained in the present investigation supply a means for making independent qualitative estimates of the contributions made by each of the above tour processes to the energy lost per cm, in lead by cosmic ray electrons. It is found that the loss by ionization and production of high energy negatron secondaries, as well as the distribution in energy among these secondaries, are in rough agreement with existing theory, except that the ionization does not apparently increase w1th energy as the theory requires. 166 direct measurements of the loss of energy in a 0.35 cm. lead plate, undergone by electrons in the energy range below 150 mev. show that these losses are subject to very large fluctuations which must necessarily be attributed to radiation of high energy photons, and that these radiative losses constitute the major part of the energy loss in lead. The mean total loss per cm. for a group of electrons with a mean initial energy of 28 mev. turns out to be about 51 mev., and 90 mev for a group with a mean initial energy of 124 mev. A comparison between these values and those computed theoretically by Bethe and Heitler, viz. 60 mev./cm. and 230 mev./cm. respectively, indicates at least a qualitative agreement between theory and experiment in the low energy range, but a complete breakdown of theory in the range above a hundred mev.

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