Geoneutrinos Detected

Neutrinos have very little mass and interact but rarely, but are made in large numbers inside the sun as a byproduct of fusion reactions. They are also routinely made in nuclear reactors and in cosmic ray showers. Terrestrial detectors (usually located underground to reduce the confusing presence of cosmic rays) have previously recorded these various kinds of nu’s.

Now, a new era in neutrino physics has opened up with the detection of electron antineutrinos coming from radioactive decays inside the Earth. The Kamioka liquid scintillator antineutrino detector (KamLAND) in Japan has registered the presence of candidate events of the right energy; uncertainty in the model of the Earth’s interior makes the exact number vague, but it might be dozens of geo-nu’s.

The neutrinos presumably come from the decays of U-238 or Th-232. They are sensed when they enter the experimental apparatus, where they cause a 1000-ton bath of fluid to sparkle. Scientists believe the Earth is kept warm, and tectonic plates in motion, by a reservoir of energy deriving from two principal sources: residual energy from the Earth’s formation and additional energy from subsequent radioactive decays. The rudimentary inventory of geoneutrinos observed so far is consistent with the theory. (Araki et al., Nature, 28 July 2005.)