Attempt to Detect a Neutral Particle of Small Mass

Editor’s Note

In 1930, Wolfgang Pauli hypothesized that nuclear beta decay might involve a second particle being emitted from the nucleus in addition to the electron. He pointed out that the puzzling continuous variation in energy of beta-decay electrons could be understood if a second, electrically neutral particle carries away a varying amount of energy. Fermi named the proposed particle the neutrino, and here Nature reports on a failed attempt by Chadwick and colleagues to detect it. If such particles do exist, they found, they must have very small mass. Indeed they do, and because they interact so weakly with other particles, neutrinos are enormous difficult to detect. This was finally achieved in 1956. Physicists later discovered that neutrinos come in three flavours.　　中文

CHADWICK and Lea have recently published the negative result of an experiment designed to examine the possibility that the continuous β-ray spectrum is accompanied by the emission of penetrating neutral particles (Proc. Camb. Phil. Soc., 30, Part 1). The energies of these particles might be distributed in such a way that they combine with those of the β-particles to form a constant energy of disintegration, a low energy β-particle being associated with a high energy “neutrino”. A strong source of radium D + E + F (radium E gives a well-marked continuous β-ray spectrum) was placed near a high-pressure ionisation chamber and an absorption curve was taken with lead screens. The radiation was all identified with the radium E and polonium γ-rays. If neutral particles are emitted, it is calculated that they cannot produce more than 1 ion pair in 150 kilometres path in air. A consideration of the possible nature of the particle shows that, if it exists, it must have small mass and zero magnetic moment.　　中文

(133, 466; 1934)