World of Scientific Discovery on Julius Ester and Hans Friedrich Geitel
After Antoine Becquerel's discovery of radioactivity in 1896, there was much speculation as to the nature of the phenomenon. For one thing, it was unclear whether this was an effect produced only by uranium (and, as later discovered by Pierre and Marie Curie, radium), or whether it could be found elsewhere in nature. The two men most responsible for revealing the truth about radioactivity--that is, that it can be found at varying levels nearly everywhere in the universe--were the German physicists Julius Elster and Hans Geitel.
Elster and Geitel met in the physics department of the University of Heidelberg; later they would teach physics together at a local secondary school. While they are most famous for the experiments they performed together, each conducted important research on his own as well. Elster built the first practical photoelectric cell (confirming many of the theories of Heinrich Hertz and James Clerk Maxwell), a photometer, and the Nikola Tesla (1856-1943) transformer. Geitel designed the photocell (no doubt inspired by his friend's work), built the first cathode ray tube, and constructed a photometer of his own.
Of the earliest collaborations between Elster and Geitel came in 1880, when they attempted to study the relationship between electricity and temperature. As in many of their future experiments, this research led to the development of new devices for accurately measuring physical effects.
Probably the most important work conducted by these two men was on the subject of radioactivity. In 1901, the German physicists discovered that radioactivity could be elicited from the very atmosphere simply by exposing a highly charged positive terminal to the (negatively-charged) air. This seemed to indicate that just about any atomic nucleus--including those in the Earth's atmosphere--could be made unstable, and thus could produce radiation.
To better observe radioactive effects, Elster and Geitel constructed a scintillation counter in 1903. This device operated on the principle that tiny crystals of zinc sulfide would emit a bright flash when exposed to radioactive alpha particles. They prepared a screen by coating it with zinc sulfide crystals; the screen was small enough to be placed under a microscope set to about 30 times magnification. As they watched, tiny scintillations would appear against the glass. Because each flash is caused by a single alpha particle, Elster and Geitel were able to count the number of particles that bombarded their screen each minute.
What Elster and Geitel confirmed with their scintillation counter was that radioactivity existed everywhere. Once this had been established, scientists began to look for radioactive sources elsewhere--often using the scintillation counter as a detection device. The efforts that followed Elster and Geitel's work led directly to the establishment of radioactive dating as a science, as well as the practice of using radiation tracing to locate uranium deposits. It was Geitel who, after years of research, suggested that the energy locked inside the atom could be a nearly inexhaustible supply for human use.
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