Scanning Earth’s Radioactive Core By Conserved Scattering

The importance of the Sun in our solar system cannot be overstated. When considered, it is quickly realised that almost all sources of energy on this planet come from the Sun. For solar power it is obvious, but wind power is caused by the temperature gradient the Sun produces and fossil fuels originally started out as plants absorbing energy through photosynthesis. The two main exceptions are tidal power, which is a conversion of the Earth and Moon’s rotational kinetic energy, and geothermal power, which is gained from nuclear decay in the Earth’s core.

This nuclear decay is producing a considerable amount of power. This paper states that 40% of the heat flow to the Earth’s surface from the interior is actually produced in radioactive decays in the crust and mantle (the rest is residual from the original formation). The main sources are potassium-40, thorium-232 and uranium-235 and 238, which all together are estimated to produce 19 terajoule (19×1012 joule) a second. It is possible to observe the antineutrinos given off by these decays, called geoneutrinos, in order to gain some understanding about the Earth’s interior.

Image result for inverse beta decay
The inverse beta decay; thank you to Annenberg Learner, for this image

Observing these antielectron-neutrinos is done through the reverse beta process shown on the left (the antineutrino combines with the proton to produce a neutron and positron). One of the main problems is that the threshold energy for this interaction,  1.8 MeV, is above the energy spectra for the potassium-40’s neutrinos. This means that although potassium may have been and still is a dominating factor in the energy given out from nuclear decay, it isn’t being recorded properly. Another feature is that the neutrino measurements we do have for uranium-238 and thorium-232 are non directional and so locating the radioisotope distributions within the crust and mantle isn’t possible.

This paper’s solution is the suggestion of using an elastic scattering between the neutrinos and electrons which would allow for the detection of neutrino flux from potassium-40 and also, depending on the detecting equipment, track the direction. Elastic scattering has no threshold energy as well as conservation laws meaning the directional information being conserved. This method would require some massive and expensive equipment, but it would allow for unprecedented scanning of the Earth’s radioactive interior and develop the field of georadiogenic heating to a new level.

Paper links: Exploring the hidden interior of the Earth with directional neutrino measurements


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