Saturday, January 05, 2008
RATE Diamond Results Duplicated and Reported
According to the paper, AMS systems should in theory be capable of detecting apparent ages of up to 100,000 years. In order to minimize sample contamination, Taylor and Southon used diamonds which are impervious to most types of contamination which had been removed from paleozoic strata.
This is related to the ability of diamonds to repel and exclude water from adhering to its surface, a very unusual property for a mineral. It was this unique physical characteristic of diamond that was the basis of our hypothesis that this surface would eliminate or significantly reduce the adhesion of carbon or carbon-containing molecules from the ion source of an AMS spectrometer that would contribute to a trace memory or sample cross talk effect.
The really interesting part is when you compare the results from multiple cuts of a single diamond compared with other diamonds. The cuts from the single diamond shows a range of 14C content between 0.00015-0.00018 fm (fm=fraction of modern - 69,000-70,000 yrs apparent age). The range from different diamonds is 0.00005-0.00021fm (68,000 - 80,000 yrs apparent age). This indicates that the differences are due to real C14 differences in the diamonds, not in instrumentation. If the problem was instrumentation, then both the split sample and the individual samples should have about the same variance, especially since (by long-age assumptions) both should be C14-dead. Instead, the carbon seems to be intrinsic to the diamonds themselves.
According to the paper:
Our measurements have confirmed our hypothesis that diamonds represent a much "cleaner" surface with respect to adhesion of carbon-containing molecules from the ion source that contribute to trace memory or sample "cross talk" effect. At this time, it is not clear to us what factors might be involved in the greater variability in the apparent 14C concentrations exhibited in individual diamonds as opposed to splits from a single natural diamond. Possible factors suggested to us are greater variability in the orientation of the crystal facies and microfractures in individual diamonds.
They also mention at the end that they plan on carrying out future experiments on artificial diamonds (in order to control introduction of C14) to see the differences in the machine output.
Anyway, it's a very interesting paper, especially since it essentially duplicates the RATE results, but done using a different laboratory and even for a different purpose (the authors did not give any indication that they doubted the long presumed age of the diamonds).