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Дата изменения: Unknown Дата индексирования: Fri Dec 21 22:03:42 2007 Кодировка: Поисковые слова: arp 220 |
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#13. Energetic ParticlesIn the cathode-ray tube of a color TV (gradually being now replaced by flat screen, based on different principles), electrons are accelerated by about 30,000 volts, so that their energy when they hit the screen is about 30,000 ev. That is actually quite a lot: those electrons move at about 1/3 the velocity of light. But then, a TV picture tube is a quite sophisticated instrument. In a doctor's x-ray machine electrons are accelerated to energies 2-3 times higher, after which they hit a target and produce a spray of x-rays.
Particle Energies in NatureHow does nature compare?
Hold it!We need bigger units:
Note on RelativityWhile the theory of relativity allows no particle with mass to move with a velocity exceeding (or even equaling) that of light, there is no limit on its energy. Close to the speed of light, however, the addition of energy only slightly increases the velocity. An ion accelerating from 0.9 to 0.99 times the speed of light needs several times more energy than the amount it needed to reach 0.9 times in the first place, though its energy makes it considerably heavier.
Why and HowWhere do single electrons and ions acquire such high energies? Excellent question. We guess magnetic and electric fields may be involved, and have learned a great deal in that direction, but the exact processes (probably more than one) remain to be nailed down. Acceleration takes place in solar flares and CMEs (see Sun) but, like a clever conjuring trick, although it happens right in front of our eyes, we still don't get it.Powerful shocks--abrupt discontinuities piled up in front of rapidly moving gas--can also do it, and at least one interesting event of this sort was observed in the Earth's magnetosphere. The most powerful shocks occur in the envelope of gas expanding from the site of supernovas, and it is widely believed that such shocks (which carry a great amount of energy) are the source of most cosmic ray particles. All those are good reasons to study the acceleration of particles in the aurora and radiation belts. The energies are more moderate, but the processes occur in a region of space which instrumented satellites can probe. As we study such acceleration processes we gradually learn how plasmas and magnetic fields interact in space, and that experience can then be applied to the rest of the universe.
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Next Stop: #14. Synchronous Orbit
Author and Curator: Dr. David P. Stern
Mail to Dr.Stern: education("at" symbol)phy6.org
Co-author: Dr. Mauricio Peredo
Spanish translation by J. Méndez