9 when does carbon 14 dating become impractical
The invention also includes a method for measuring the ratio of one isotope to another in a carbon containing composition with a statistical precision of better than 5% in less than 5 minutes.
The method for measuring the ratio comprises producing the carbon compound from the carbon in the carbon containing composition.
Sufficient C ions of both isotopes are then produced and detected from the carbon compound to provide a sufficient number of counts of each carbon isotope by mass spectrometry to determine the ratio of the isotopes which is the same as the ratio of the number of counts.
When the quantity of one of the isotopes is known prior to analysis by the method in accordance with the present invention, the quantity of the other isotope can, of course, be readily calculated from the quantity of known isotope.
Furthermore, when better analytical precision is desired (e.g., a statistical precision better than 5%), even higher quantities of carbon 14 must be injected.
All of the carbon 14 injected into the person would almost certainly not become concentrated in the sample taken from the person and, in addition, since the sample being considered must be adjusted for the biological half life of the compound, a substantial excess of carbon 14 would initially be required to compensate for loss due to biological excretion or biochemical transformation.Since the producing efficiency can vary with time due to possible changes in the ion producing conditions, and even in the ion detecting conditions, an unknown quantity of an isotope is usually calculated as a ratio to a simultaneously detected quantity of a different known carbon isotope.The ratio of one carbon isotope to another can be determined even if the producing and detecting efficiency is not known since the same producing and detecting efficiency will apply to both isotopes.A method for detecting and quantifying a carbon isotope at quantities of less than 1×10-12 gram at a statistical precision of better than 5% in a time period of less than 5 minutes by producing a carbon compound, selected from CO, CS2, CO2 and elemental carbon, from the carbon containing composition to...gram at a statistical precision of better than 5% within a time period of less than about five minutes, said method comprising producing a carbon compound selected from the group consisting of elemental carbon, CO, CS11.