Facts and Mysteries in Elementary Particle Physics by Martinus J. G. Veltman

Facts and Mysteries in Elementary Particle Physics by Martinus J. G. Veltman

Author:Martinus J. G. Veltman
Language: eng
Format: epub
Publisher: World Scientific
Published: 2003-04-14T16:00:00+00:00


Victor Hess (1883–1964, Nobel prize 1936) and Theodor Wulf (1868–1946). These physicists discovered cosmic rays. In 1910 Theodor Wulf, a Jesuit College teacher in Valkenburg, the Netherlands, made a sensitive electroscope (Wulf’s electroscope). It was known that such an instrument, after being charged, slowly lost its charge and it was believed that this was due to radiation from the earth. It was known at the time that radio-activity would discharge such an instrument. Wulf asked the French physicist Langevin for help to do the experiment at the top of the Eiffel tower. The result, carefully analyzed, was unexpected: the electroscope discharged much faster than anticipated given the absorption of radiation by the air!

An electroscope is a very simple device of which the main part consists of two conducting leaves. When charging this setup the leaves will repel one another, and they will spread out, as in the picture. If a charged particle passes by, knocking off electrons from atoms, the resulting ions or electrons drift to the leaves, thereby discharging them, and they fall back.

Hess decided to investigate the issue in a systematic manner. He started off with some experiment in a meadow in Vienna. In order to get higher up he became a balloonist, taking Wulf’s electroscope to heights of up to 5 km. After some 8 flights (sometimes unmanned), a few of them at night and one during a solar eclipse (to eliminate the sun as a source) he established that at high altitudes the effect was stronger than near the ground, concluding that the effect was due to radiation from outer space. Millikan entered the field later on, and having a better sense of public relations coined the name cosmic rays (replacing the name ultra-radiation). At first, on the basis of his own experiments, Millikan doubted Hess’s results, but later on he turned around, and in fact became more prominent in the public eye than Hess. The Swedes however recognized the facts and awarded half of the 1936 Nobel prize to Hess for the discovery of cosmic rays (the other half to Anderson). Perhaps they should have included Wulf.



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