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GR9277 #25 |
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Problem
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\prob{25}
In experiments located deep underground, the two types of cosmic rays that most commonly reach the experimental apparatus are
- alpha particles and neutrons
- protons and electrons
- iron nuclei and carbon nuclei
- muons and neutrinos
- positrons and electrons
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Advanced Topics }Particle Physics
Choice (A) and (C) involve atoms, which are quite massive. Choice (B) involves protons, which are also pretty massive. Massiveness eliminates three choices, leaving just (D) and (E).
Neutrinos are massless, but muons aren't. Both positrons and electrons have the same mass. Massiveness has lost its charm. (No pun intended.)
According to David Schaich, the Super-Kamiokande
and the Antarctic Muon and Neutrino Detector Array (AMANDA) are both located deep down underground to avoid interaction with other particles. Thus, with the hindsight of this bit of trivia, choice (D) is correct.
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Alternate Solutions |
Shoshe
2006-11-03 11:18:36 | Neutrinos only experience the weak interaction, which makes them hard to detect. If you try to do a neutrino experiment on the Earth's surface, you'll have a horrible signal-to-noise ratio. Neutrino detectors are generally located underground because as cosmic rays go through the Earth, most of the particles other than neutrinos (pions, muons, antiprotons, etc.) will interact with "stuff" and not reach the detector. The deeper underground the detector is, the fewer false positives. In general, "underground particle experiment" = "neutrino experiment". Choice (D) is the only one that mentions neutrinos. |  |
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Comments |
sirius
2008-11-04 00:13:23 | this problem is almost pure trivia. while one can spend time thinking about it, i'm positive ETS put it in there for trivia's sake. |  | HariSeldon
2008-06-29 11:30:45 | You can also eliminate E with the knowledge that electrons have a relatively short interaction length, while muons travel much farther before interacting. | | sharpstones
2007-03-26 17:50:04 | it's worth noting as well that Positrons are antimatter particles which tend to have a short lifespan in any place with matter. (remember matter & antimatter = boom! energy) So they would no be able to penetrate the earth from outer space. | | Shoshe
2006-11-03 11:18:36 | Neutrinos only experience the weak interaction, which makes them hard to detect. If you try to do a neutrino experiment on the Earth's surface, you'll have a horrible signal-to-noise ratio. Neutrino detectors are generally located underground because as cosmic rays go through the Earth, most of the particles other than neutrinos (pions, muons, antiprotons, etc.) will interact with "stuff" and not reach the detector. The deeper underground the detector is, the fewer false positives. In general, "underground particle experiment" = "neutrino experiment". Choice (D) is the only one that mentions neutrinos. | |
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