The Birth of Nuclear Physics

Abstract

The next reading selection, which is divided between the next two chapters of this volume, originally appeared in 1906 in the Philosophical Journal. Herein, Rutherford addresses the question: what is the identity of the newly-discovered α-particle? In order to answer this question, Rutherford first needed to determine the properties of the α-particle—specifically its speed and charge-to-mass ratio. After all, this is how his mentor, J.J. Thomson, characterized the unique properties of the electron a few years earlier. Rutherford was not the first to attempt such measurements on α-particles. What difficulties did previous researchers encounter? And how were Rutherford’s experiments different?

The $\alpha$ radiation from radium is very complex, and consists of four groups of $\alpha$ particles, each of which is made up of $\alpha$ particles which escape at widely different velocities.

—Ernest Rutherford