Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27r.289s&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 289-289
Other
2
Scientific paper
In [1] we reported on the first long-sought evidence for live 60Fe in the early solar system. 60Fe decays with T(sub)1/2 = 1.5 My [2] and forms, via 60Co, the stable nuclide 60Ni. The importance of the 60Fe-60Ni system is determined by the fact that it could serve as a sensitive chronometer for early solar system events and, if 60Fe was present in sufficient amounts, as a heat source for melting and differentiation of early formed planetesimals. To search for the presence of 60Fe in the early solar system we have chosen the relatively unbrecciated eucrite Chervony Kut (CK) whose igneous origin is well established [3]. Their extremely high Fe/Ni ratio clearly suggests that eucrites are the basaltic products of planet-wide melting and differentiation and, together with an old age, are prerequisites for the detection of effects from the decay of 60Fe and for the demonstration of its large-scale occurrence. The first analysis of a fine-grained "bulk" sample of CK with 56Fe/58Ni = 3.4 x 10^4 revealed a distinct and well resolved excess of 60Ni of 6.6 +- 0.6 epsilon units [1]. Considering several potential sources for this effect it has been concluded that this excess is due to the decay of 60Fe and represents the first clear evidence for the existence of live 60Fe in the early solar system [1]. We calculated the 60Fe/56Fe ratio at the time of Ni depletion as ~7.5 x 10^-9. It was also shown that the decay of 60Fe could provide considerable amounts of heat within planetesimals during the very early stages of accretion. After this original discovery we set out to a) provide corroborating evidence from other samples of CK and b) ascertain whether 60Fe was still alive at the time of solidification of CK and if so, attempt to determine the 60Fe/56Fe ratio at that time. It was found that Ni is very heterogeneously distributed within the meteorite and may reside mainly within tiny metal grains rather than within the major mineral phases. For example, several 'bulk' samples had Ni concentrations ranging from >6 ppm down to 0.5 ppm. Mild HCl washes of Px separates contained more Ni than the actual Px fractions. Nevertheless, all samples with sufficient amounts of Ni for isotopic analysis showed excess 60Ni ranging from 2 to about 14 epsilon units, clearly confirming the earlier result. However, no correlation exists between excess 60Ni and Fe/Ni. If we assume that CK represents a closed system with respect to Ni, and 60Fe was 'dead' at the time of solidification, we should expect the same 60Ni excess in all samples analyzed regardless of Fe/Ni, which is obviously not the case. Different 60Ni excesses can be understood only if some 60Fe was still alive at the time of crystallization of CK. Post-crystallization mobilization of Ni caused redistribution of Ni relative to Fe at a later time and, thus, obliterated any correlation of 60Ni excesses with Fe/Ni. A metamorphic event is also indicated by earlier Rb-Sr and 40Ar/39Ar results [4]. Unfortunately, the incompatibility of Ni and its mobility during metamorphic disturbances may hamper the future usefulness of the 60Fe-60Ni system as a chronometer. [1] Shukolyukov A. and Lugmair G.W. (1992) Lunar Planet. Sci. 23, 1295. [2] Kutschera W. et al. (1984) Nucl. Instrum. Methods B5, 430. [3] Gooding J.L. et al. (1979) Lunar Planet. Sci. 10, 446. [4] Wooden J.L. et al. ( 1979) Lunar Planet. Sci. 10, 1379.
Lugmair Guenter W.
Shukolyukov Alex
No associations
LandOfFree
60Fe -- Light My Fire does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with 60Fe -- Light My Fire, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and 60Fe -- Light My Fire will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1209921