When does carbon 14 dating become impractical
The carbon isotopes which are usually detected and quantified, in accordance with the present invention, are carbon 12 ( gram.
In addition, such quantities can be quantified at a statistical precision of better than 5% and usually better than 1% within a time period of less than about 5 minutes and even substantially less than 1 minute.
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.
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.
The ion producing efficiency can then be calculated for the known quantity of the isotope other than the isotope to be quantified.
The detection and quantification of carbon 14 in an amount even as low as 1×10 gram are quantities which are undesirably high to permit the use of carbon 14 as an in vivo biological radioactive tracer in humans.Furthermore, the method of the invention can be used for measuring the ratio of one carbon isotope to another in a carbon containing composition with a statistical precision of better than 5% and usually easily better than 1% at ratios of one isotope to another of 1:1,000,000 or better.Furthermore, such ratios can be determined in less than 1 minute at a statistical precision of 1% or better.In accordance with the present invention, a carbon compound selected from the group consisting of elemental carbon, carbon monoxide (CO), carbon disulfide (CS ions are then produced and detected from the carbon compound at a known producing and detecting efficiency to provide a sufficient number of counts per minute by mass spectrometry of ions of the carbon isotope to be detected and quantified.The detecting efficiency is a known characteristic of the detector employed and the producing efficiency is usually determined by simultaneously producing ions from a known quantity of an isotope other than the isotope to be quantified.