The Wilson cloud chamber was superseded by the bubble chamber, in which a superheated liquid (hydrogen, propane and others) replaces the supercooled vapor. When an atom is hit by an elementary particle, the extra local energy vaporizes the liquid, and a tiny bubble appears at the point of collision, again making the path of the particle visible.
In recent years chemists have developed compounds (polymers, or very long molecular chains of identical building blocks) that re-main superheated at room temperatures and can be carried about in sealed test tubes in one's breast pocket. They are little bubble chambers producing small bubbles when hit by particles of a cer-tain energy, in particular neutrons. The reason why this is impor-tant is that the number of bubbles is directly proportional to the dose received by the wearer of this dosimeter. He can count the bubbles on the spot (for example, by xeroxing the tube and count-ing them on the projection).
Current dosimeters have to be evaluated by special, expensive equipment to which the dosimeter (in the form of a badge, or for radon detection, a canister or other object) must be taken
¾and often sent by mail. Directly reading radiometers do not have this drawback, but are usually very insensitive. They are often plugged by ads in hobbyist magazines, sometimes headed by a panicky "If you live within 100 miles of a nuclear plant . . . " Some of them start reading only at 50 mR/hr, which would have been quite useful to all around Chernobyl who had not yet noticed the plant was on fire. (Natural background is about 0.01 mR/hr).Moreover, these instruments will detect only the alpha, beta and gamma radiation emanating from radioactive sources, but not neutrons, which have hitherto needed more complicated monitors. The pocket-sized neutron bubble detectors have now become commercially available (Siemens Gammasonics Inc, Health Phys-ics Div., Des Plaines, Ill., tel. 800-323-6015).
Comparatively few people, mainly in the nuclear industry, aca-demic research and the military, are exposed to neutron radiation, and a gamma-ray detector of this type would be more useful. It was announced as "almost ready" in May, but it seems that a hitch has developed and the release has been indefinitely postponed.
Bubble, bubble, toil and trouble... and Macbeth, of course, was a Scotsman, too!
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Vol. 16, No. 3
Newsletter: Access to Energy Newsletter Archive Volume: Issues Issue/No.: Vol. 16, No. 3 Date: December 01, 2004 02:09 PM (For actual publication date see newsletter.) Title: A tale of two gases
Copyright © 2004 - Access to Energy Newsletter Archive
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