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Solar-flare produced 3He in lunar samples

Nature volume 286, pages 788790 (21 August 1980) | Download Citation

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Abstract

Lunar rocks and soils undergo long-term irradiation by solar and galactic cosmic rays (SCR and GCR) leading to compositionally-distinct spallation spectra for noble gases1,2 and leaving behind fossil records characteristic of different irradiation features. Because the SCR effects are restricted to the first few millimetres of rocks and soils in contrast to GCR, various studies based on solar flare tracks3,4, thermoluminescence5, and radionuclides3,6 over the past decade have aimed to decipher these fossil records bearing the imprints of the low (SCR) and high (GCR) energy irradiation phenomena. These studies have greatly helped our understanding of the energy spectra and fluxes of charged particles streaming out of the Sun. We have already reported quantitative studies, aimed at isolating the SCR and GCR produced Ne and Ar isotopes in several lunar soils and rocks1,2 and have calculated their solar flare exposure ages which agree with the ‘surface’ exposure ages based on 26Al and particle track studies3. We describe here, for the first time, using 3He in samples from three different depths of lunar rocks, a method for deducing the absolute SCR (flare) proton fluxes in the past few million years which compare favourably with those derived from 26Al and 53Mn studies3,6 of other lunar samples.

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Author information

Affiliations

  1. Physical Research Laboratory, Ahmedabad 380 009, India

    • M. N. Rao
    •  & T. R. Venkatesan

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DOI

https://doi.org/10.1038/286788a0

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