Scintillation Counter
The ability of radiation to produce luminescence in certain types of materials was recognized by Antoine Henri Becquerel (1852-1908) in 1899. The first application of the principle in a detecting device was made by William Crookes in 1903 with the invention of the spinthariscope. Crookes' spinthariscope consisted of a brass tube with a zincsulfide screen at one end and a magnifying lens at the other end. A tiny crystal of a radioactive salt was mounted on a pin about a millimeter from the zinc sulfide screen. Radiation from the salt struck the screen, producing tiny flashes of light that could be viewed through the lens.
The potential for using such a device as a radiation detector and counter was noted by a number of investigators. Ernest Rutherfordwrote in 1904 that the Crookes device "would offer a very convenient means of actually counting the number of particles... if each particle gave rise to a flash of light." Working with Hans Geiger (1882-1945), Rutherford showed that such a method could be used for counting alpha particles and was as accurate as was the Geiger counter. The first working scintillation counter was apparently made at about this time, however, by the German physicist Ernst Regener (1881-1955), who used diamond rather than zinc sulfide as the scintillation source.
A number of early researchers used primitive scintillation counters in their work on nuclear reactions. A fundamental drawback of the instrument, however, was the difficulty of observing and counting individual flashes of light. As a result, scintillation counters became less popular than Geiger counters, cloud chambers, and other instruments that were easier to use.
By the 1930s, a solution to the problem of observing flashes—the photomultiplier tube--had been invented. In the photomultiplier tube, a single flash of light falls on a metal plate, causing the emission of a number of electrons. These electrons, in turn, are accelerated towards other metal plates, resulting in the release of even larger quantity of electrons. After a number of repetitions, the single flash of light has been multiplied enough times to produce an electrical current that can be easily read and recorded.
Scintillation counters are now used in a wide variety of applications in nearly every field of science. They can be produced with very small dimensions, making them useful in situations where other detectors might be too bulky. Where conditions demand, they can be made very large in order to scan a broad area of an experiment. Since scintillations occur very quickly (as fast as 10-9 second), they are sometimes more efficient at recording all the events that occur in a particular experiment, a characteristic not shared by some other types of detectors.
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