A hundred years ago…

23 September 1998

In 1895, a chance discovery by Wilhelm Conrad Röntgen changed the face of science. It was the dawn of a new branch of physics ­the investigation of subatomic phenomena. Following the centenary of the Röntgen discovery in 1995, an occasional series of articles in CERN Courier looks back at what happened one century ago.


Röntgen’s discovery of X-rays in 1895 startled the world of science and immediately motivated other researchers to investigate fresh paths. In the Cavendish Laboratory in Cambridge, J J Thomson ordered a general mobilization of research effort on the new Röntgen phenomena. The result was that Thomson himself discovered the electron in 1897 and a young New Zealand student called Ernest Rutherford stopped playing about with his electromagnetic wave generator and turned to the new subatomic physics instead.

In 1896, the discovery by Henri Becquerel that uranium emitted mysterious radiation had provided fresh physics stimulation. However, in contrast to the immediate impact of the earlier Röntgen discovery, the implications of Becquerel’s radioactivity breakthough took longer to appraise. Becquerel himself turned to the investigation of another new discovery, the Zeeman effect.

In Paris, one resolute young researcher was continuing with the study of Becquerel rays ­ Marie Curie. Working with her husband, Pierre, she showed that the ability of uranium compounds to emit the rays was a property of uranium itself, and went on to coin the name “radioactive”. During 1898, in a heroic analysis of uranium-rich minerals, Marie and Pierre Curie identified two new radioactive substances ­ polonium and radium.

Marie Curie, the driving force in this work, did not finish her PhD thesis until 1903, that same year sharing the Nobel Physics prize with her husband and with Henri Becquerel for their work on radioactivity. Pierre Curie was killed in a Paris traffic accident in 1906, and Marie succeeded him as Sorbonne professor.

On the other side of the Channel, Rutherford had been working with Thomson, studying the gas ionization generated by X-rays and developing the parallel-plate electroscope. In 1898 the young New Zealand student turned to the ionization produced by Becquerel rays. While previously Rutherford had been looking at the effects of radiation (“the electrified gases from Röntgen’s rays”), this time he focused on the nature of the radiation itself.

Setting the style for his subsequent work, simple but incisive methods produced remarkable insights. By covering his sources with layers of foil, Rutherford showed that Becquerel rays were inhomogeneous, with at least two distinct components, one of which was absorbed by just a few foils, which he called alpha-radiation, the other ­ beta-radiation ­ being more penetrating.

Rutherford’s initial paper on radioactivity was completed at Cambridge on 1 September 1898, just before he left to take up the MacDonald Chair of Physics at McGill University, Montreal, where he was to continue his epic studies of radioactivity.

One hundred years later, the Curie­Rutherford nomenclature of radioactivity and alpha particles remains in everyday use.

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