Physics Question #396

Roman, a 15 year old male from the Internet asks on June 17, 1998,

How do scientists detect nutrinos when they have no mass and no charge?

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The answer

Chris Waltham answered on June 17, 1998

Neutrinos behave like chargeless electrons. Electrons are affected by the electromagnetic (EM) and the weak forces (although the latter is hard to see against the more powerful EM force). Neutrinos only have weak interactions, which actually have a similar strength to the EM interaction but they exert it over a very small distance. Neutrinos interact with all atomic nuclei (to varying degrees), and with electrons, but getting close enough to interact is so improbable that an individual neutrino can pass through enormous thicknesses of material (like light-years) with only a tiny chance of interaction. We can see interactions of solar and cosmic-ray-induced neutrinos only because

  • the fluxes are huge (10^15 per m^2 per s for solar neutrinos)
  • our detectors are huge (1000 tons or 10^33 target atoms)

If you are interested further, see the Sudbury Neutrino Observatory homepage.

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