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In Brief

Recent advances in the understanding of neutrinos and improved detection instruments have recently given an intriguing glimpse into the deep interior of the Earth, says Roger Mason.

Geoscientist 20.6 June 2010

An article in the May 2010 issue of Scientific American1 included the comment: “Our Earth glows feebly in neutrinos”. Neutrinos are the most elusive nuclear particles and most of them travel right through the Earth. A few interact with matter, giving brief flashes of light and a stream of neutrinos from the core of the Sun was detected several decades ago. Detection systems are often buried deep in disused mines where the majority of cosmic ray particles have been stopped by overlying rocks. Identification of neutrino interactions requires large volumes of matter such as water or ice to interact, very sensitive detectors, long periods of measurement, and many careful checks to eliminate flashes from particle interactions that do not involve neutrinos.

Detection systems have recently improved and even better detectors are on the way, either under construction or at the planning stage. Neutrinos change their energy, mass and a property called ‘flavour’ as they travel, but it is possible to identify some of the nuclear reactions that released them. For instance, neutrinos from the Sun are produced by the standard solar nuclear fusion reaction. Gelmini and her colleagues describe other extra-terrestrial neutrino sources and their nuclear reactions, for example supernova explosions.

In a paper submitted to Elsevier in March 2010, Bellini2 and a large team of colleagues who operate the Borexino neutrino detector at Laboratori Nazionali del Gran Sasso in Italy explain how they have detected neutrinos generated within the Earth. They were able to tell the difference between neutrinos released by natural nuclear decay and those formed in artificial nuclear reactors. The natural neutrinos’ characteristics suggest that most of them formed by nuclear decay reactions of uranium and thorium isotopes, familiar to Earth scientists from geochronology. The system does not detect neutrinos from potassium decay. Although only a small number of neutrinos were found, there are more than standard estimates of Earth composition would indicate, raising the intriguing possibility that there may be some other type of nuclear reaction occurring in the deep Earth, possibly interaction between mysterious dark matter and the core.


  1. Graciela B. Gelmini, Alexander Kusenko and Thomas J. Weiler, 2010. Through Neutrino Eyes, Scientific American 302, 20-27 (May 2010).
  2. G. Bellini and other members of the Borexino Collaboration Team, 2010. Geo-neutrinos, manuscript Geo-Nus-1003.0284v2[1] [in press].