‘1932’

Abstract

In January 1932, a young British researcher, James Chadwick, read a paper published in the journal of the French Academy of Sciences, Comptes Rendus by a husband-and-wife team, Frederick and Irene1 Joliot-Curie. In that paper, they described how they had bombarded a piece of the gray, toxic metal beryllium with α (alpha) particles² shot out of a sample of the radioactive element polonium. What emerged from the experiment was a highly energetic yet intangible form of radiation. Although they couldn’t detect the radiation directly, they were able to detect protons punched out of a range of materials placed in the path of the new radiation. What puzzled them was this new form of radiation passed through almost anything more freely than any other form of radiation they had previously encountered. Earlier experiments by Walter Bothe and his student Herbert Becker in Germany had shown that the radiation would pass through 200mm of lead. Not bad, considering it takes less than 1 mm of lead to stop the most energetic form of energy then known, y (gamma) rays.³ This new radiation was ‘so hard that one can hardly doubt their nuclear origin’.⁴ Both teams assumed that the unknown radiation must in fact be an even more energetic form of gamma rays; after all, it was known that gamma rays could knock electrons out of metals, so why not protons out of the nuclei of other materials? But this was only part of the story; Chadwick knew the rest. He knew what they had found but had not identified. Electrified into action, he repeated and extended the experiments and, in the course of three weeks of frantic, intense experimentation, demonstrated the existence of the third component of the atom, the neutron. The discovery was to have profound consequences for events in the heavens and here on Earth.