Uppsala Natural Radiocarbon Measurements IV

Abstract

The following list covers most of the samples measured at the Uppsala C14 laboratory since the last list (Uppsala III) except for all the samples utilized for determining the increase of the C14/C12 ratio due to explosion of nuclear devices and the few samples measured with a new proportional counter.The technique used is the same as previously described by Olsson (1958) and the pretreatment is that which has been used earlier (wood, charcoal, peat, gyttja and other organic sediments are boiled with HC1, 1 to 2%, washed with distilled water, kept in NaOH, 1 to 2%, at +80°C over night, washed with distilled water and finally acidified to pH about 3 before being dried) except for Foraminifera tests, see below.The reference sample is 95% of the activity of the NBS oxalic-acid standard. Any corrections for apparent water ages are thus not included here, but will be discussed in later papers dealing with the marine samples. Corrections for deviations from the normal C13/C12 ratio (-2S.0% in the PDB scale) are applied for the unknown samples. Our oxalic acid was measured by Craig (1961) and has a C13/C12 ratio of -18.97% and corresponds to the accepted standardized value, -19%, which should be used for age determinations (Editorial Statement in Radiocarbon, v. 3). Two new combustions of oxalic acid have not shown any significant difference in their C13 content relative to the oxalic acid 1 sample measured by Craig.The value 5570 yr has been used for the half-life of C14. Results are expressed in years before 1950 (b.p.). Errors include the standard deviations (a) of the counted particles as well as the error in the δC13 values. When the activity is very low, so that 2σ corresponds to a possibility of infinite age, 2σ has been used instead of σ.Several samples had to be diluted with CO2 from an old source to bring them to the normal working pressure of 3 atm.