Amongst accelerator laboratories there has been mooted the theoretical possibility of extended range dating to 75 000 yr , at present this seems difficult to attain because of the problems in accurately differentiating between ions that mimic the mass and charge characteristics of the C14 atom.
Beukens (1994) for instance has stated that this means the limit of the range for his Isotrace laboratory is 60 000 yr which is very similar to the conventional range.
It is vital for a radiocarbon laboratory to know the contribution to routine sample activity of non-sample radioactivity.
A copy of this paper may be found in the Radiocarbon Home Page The radiocarbon age of a sample is obtained by measurement of the residual radioactivity. T (National Institute of Standards and Technology; Gaithersburg, Maryland, USA) Oxalic Acid I (C). The activity of 1890 wood is corrected for radioactive decay to 1950.
This is calculated through careful measurement of the residual activity (per gram C) remaining in a sample whose age is Unknown, compared with the activity present in Modern and Background samples. Thus 1950, is year 0 BP by convention in radiocarbon dating and is deemed to be the 'present'.
'Normalized' means that the activity is scaled in relation to fractionation of the sample, or its delta C13 value.
All D14C values are normalized to the base value of -25.0 per mille with respect to the standard carbonate (VPDB).