Direct Measurement of Alpha Particle Activities of Rocks and Determination of Thorium

Author: Raitt, Russell Watson

Year: 1935

Degree: Dissertation (Ph.D.)

Advisor: Millikan, Robert Andrews

Committee Member: Unknown, Unknown

Option: Physics

DOI: 10.7907/3h26-dk66

Abstract

The most important applications of the measurements of radioactivity in rocks require knowledge of only one quantity, the rate of production of alpha particles.

The common procedure has been to calculate this quantity from the radium and thorium concentrations determined by emanation methods. This procedure involves considerable experimental difficulties, and the result is de pendent on an accurate knowledge of the decay constants of radium and thorium.

The method herein described measures the total alpha activity directly and simply, by counting the alpha particles emitted into an ionization chamber from a layer of finely powdered rock whose thickness is small compared to the ranges of alpha particles in the rock. Counting of the alpha particles is accomplished by means of an FP-54 electrometer tube set at a sensitivity great enough to reveal single alpha particles, which are recorded as sudden deflections of the recording galvanometer.

This method was applied to fourteen cosmic ray rocks whose radium content was determined by the direct fusion method. Measurement of the total alpha activities of the se rocks has yielded their thorium content and enabled a correlation with local ionization to be made based on both the uranium and the thorium series.

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