Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1971
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1971ap%26ss..13..249s&link_type=abstract
Astrophysics and Space Science, Volume 13, Issue 1, pp.249-266
Astronomy and Astrophysics
Astrophysics
13
Scientific paper
The nucleus26Al(τ1/2 = 7.4 × 105 yr) has long been considered as a possible heat source during the formation of the solar system. Recent experimental work has found no evidence for26Al at the time of final solidification of the meteorites. Due to the short half-life these measurements do not rule out the possibility that26Al was a significant heat source a few million years prior to final solidification. For26Al to be an effective heat source in the early solar system it is necessary for the ratio26Al/Si to be ≳2×10-7 at the time of a solidification. The nucleosynthetic yields of26Al by silicon burning, carbon burning, and spallation are discussed. It is shown that26Al can be synthesized in carbon and/or silicon-burning supernovae. However, time scales in the early solar system make it more likely that26Al, if present in planets, was synthesized by a proton irradiation in the early solar system. An integrated proton flux >4×1018 cm-2 is shown to be necessary in order for26Al to be a significant heat source. No conclusive evidence has been observed for an irradiation of this magnitude. Therefore, unless such evidence is found, it should be assumed that26Alwas not involved in the formation of the solar system. In addition, the production of26Al in cosmic rays is discussed and it is shown that either resolution of the Al isotopes in the cosmic rays or accurate measurements of the variation with energy of the cosmic ray abundance ratios Al/Si and Mg/Si can be used to determine the ‘age’ of the cosmic rays, τC.R.. Current abundance data are extremely uncertain; however, the trend tends toward values of τC.R. ≳ 106 yr.
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