Equal electrical charges repel each other, and an electroscope is a time-honored instrument for measuring charge by the distance to which two equally charged light objects will repel each other against some other force (such as gravity). Until they are discharged by a conductor, they should stay in their position forever.
Well, they don't. The charge gradually disappears, and for more than a century, physicists could not understand why. The puzzle was solved in 1911: The charge leaks away through ionized air (a partial conductor), and what ionizes it are cosmic rays¾radiation from interstellar space, mainly from our own home galaxy, the Milky Way. Nuclei of hydrogen and helium (mostly) with enormous energies shoot into the atmosphere, where they cause secondary radiation from the atoms they hit, and this cascade continues until the energy of the primary particles is dissipated. The intensity of this radioactivity decreases as the atmosphere gets denser and absorbs it; that is the reason why Colorado and other mountain states have roughly double the natural background radioactivity of regions at sea level. (Colorado, with double the national average in radioactivity, haha, has 70% of the national average in cancer incidence.)
But back to the computer: Just as cosmic radiation discharges electroscopes, so can it very occasionally turn a 1 into a 0 in a computer memory location and cause an error. How often? In a given location, roughly once every 7.5 million years, but since the total number of such locations in a mainframe computer is of the order of 64 million (64 megabits), the time between such "soft fails" is reduced to something like 6 weeks. Countermeasures: Run the computer at lower altitudes behind thick concrete shielding (however, concrete gives rise to other special effects).
[More: "Effect of cosmic rays on computer memories" by Ziegler and Lanford, Science, 16 Nov. 79, pp.776-788.]
All this is getting a bit far away from energy, but we have some clearing up to do on a related subject. Why is it, asks a reader, that killing bacteria by strong radiation to preserve food will leave the food unharmed (AtE Apr.79), whereas, say, the inside walls of the containment building at TMI-2 have become strongly radioactive?
The answer is that radioactivity is a nuclear phenomenon, and to induce it in originally stable atoms, one has to get inside their nuclei. This can be done with heavy, energetic particles (usually neutrons, but also alpha or even beta particles), but not with gamma rays, which are electromagnetic radiation of the same type as light. They cannot make the nucleus of the atom disintegrate, they can only tear off electrons from its shell, i.e., ionize it. (This is how they kill cells, and ultimately bacteria.) The food is irradiated, from a distance, with gamma rays that ionize, but cannot penetrate the nuclei. If a source of neutrons or alpha rays were buried in the food, the immediately neighboring matter could indeed become radioactive, just like the walls at TMI-2.
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Vol. 7, No. 8
Newsletter: Access to Energy Newsletter Archive Volume: Volume 7 Issue/No.: Vol. 7, No. 8 Date: April 01, 1980 03:23 PM (For actual publication date see newsletter.) Title: Anniversary of the Grand Disaster
Copyright © 2004 - Access to Energy Newsletter Archive
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