Astrophysics and Space Science

, Volume 144, Issue 1–2, pp 337–346 | Cite as

Temporal variations of low-energy cosmic-ray protons on decadal and million year time-scales: Implications to their origin



We discuss the present day information on the prehistoric proton radiation in the solar system at 1 AU based on activation of lunar surface materials, in relation to our present day knowledge of their contemporary fluxes in solar flare events and during quiet time. The bulk of the prehistoric radiation can be attributed to its origin in solar flares. Its energy spectrum is, however, harder than the solar flare radiation observed during solar cycles 19, 20, and 21 (1954–1986). The implications of the data to other sources of particles and/or acceleration mechanisms in the interplanetary region are discussed.


Radiation Temporal Variation Flare Energy Spectrum Solar System 
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Copyright information

© Kluwer Academic Publishers 1988

Authors and Affiliations

  • D. Lal
    • 1
    • 2
  1. 1.Scripps Institution of OceanographyLa JollaUSA
  2. 2.Physical Research LaboratoryAhmedabadIndia

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