Mathematics – Logic
Scientific paper
Mar 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993gecoa..57.1053e&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 57, Issue 5, pp.1053-1069
Mathematics
Logic
16
Scientific paper
U-rich minerals were investigated for the products of radioactive decay, fission and specific nuclear reactions induced thereby. Geologically undisturbed uranium minerals with concordant U-Pb ages were used to determine the product of the 238 U spontaneous fission decay constant sf and the yield i Y sf of a specific Xe or Kr isotope, the isotopic ratios of spontaneous fission xenon and krypton and the 136 Xe / 86 Kr spontaneous fission ratio. Values of (5.7 ±0.4) · 10 -18 / a and 6.1 ± 0.1 were obtained for sf · 136 Y sf and ( 136 Xe / 86 Kr ) sf , respectively. With our result for sf · 136 Y sf and literature data on 238 U spontaneous fission yields, we propose that the proper value for sf is around 8.6 · 10 -17 /a rather than the 6.4 · 10 -17 / a as mainly proposed by fission track investigators. Isotopic ratios of neon and argon differ significantly from atmospheric composition. No evidence for nucleogenic neon and argon from strongly asymmetric fission or from ( n , ) or ( n , ) reactions was found. These gases are produced by the nuclear reactions 18 O ( , n ) 21 Ne , 19 F ( , n ) 22 Ne , 35 Cl ( , p ) 38 Ar and 35 Cl ( n , ) 36 Ar as already proposed in 1954 by Wetherill. For these reactions the production ratios P(21) norm , P (22) norm and P(38) norm of 21 Ne nuc , 22 Ne nuc and 38 Ar nuc relative to the -dose and the target element concentrations in the minerals were deduced. The problem of diffusional 4 He losses was circumvented by using fissiogenic Xe as a measure of the -dose. The contributions of 22 Ne nuc and 38 Ar nuc to the Earth's atmosphere are negligible, whereas up to 2.4% of 21 Ne in the atmosphere may be nucleogenic.
Eikenberg Jost
Signer Peter
Wieler Rainer
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