Paul Villard

Today is the birthday of Paul Villard, the discoverer of gamma rays. He was born in Saint-Germain-au-Mont-d’Or, near Lyon, France, in 1860. Villard is often forgotten for his contributions to the understanding of radioactivity and the electromagnetic spectrum, overshadowed by Henri Becquerel (who discovered radioactivity) and Wilhelm Röntgen (the discoverer of x rays). Around 1900 Villard began studying the radiation emitted by radium salts, including some provided by Marie and Pierre Curie. He quickly identified beta radiation, which had been discovered by Ernest Rutherford in 1899. Because beta rays are actually negatively charged particles, they get deflected by a magnetic field. But Villard also observed another kind of radiation that was unaffected by a magnetic field and was able to penetrate a 0.2 mm thick layer of lead foil. His discovery, which he presented in April and May of 1900, didn’t get much attention at first. But scientists would later confirm that Villard had discovered a new variety of electromagnetic radiation, with more energy than even x rays. Following the Greek letter notation of Rutherford, it was called gamma radiation. Today astronomers use specialized telescopes to observe gamma rays emitted by mysterious cosmic explosions that are hundreds of times as bright as supernovas. (Photo courtesy of the Archives de l’Academie des Sciences, Paris, France)

Date in History: 28 September 1860