engleski

Rudjer Bošković Institute radiocarbon measurements II

The present list contains dates of samples measured since our previous list (R., 1971, v. 13, p. 135-140). As before, age calculations are based on the Libby half-life 5568 ± 30 yr, and reported in years before 1950. The modern standard is 0.950 of the activity of NBS oxalic acid, giving a net counting rate of 21.68cpm. The background count is measured by a series of inactive samples such as marble, anthracite, petroleum coke, and old natural methane. Background count of these samples give a mean value of 6.05cpm. It is observed that marble always gives the highest value of background count while natural methane gives the lowest. Results, however, are within ± I Q of the mean value. The reduction of nearly 3cpm in background count with respect to previous values listed in R., 1971, v. 13, p. 135-140 is obtained by adding a 10cm layer of low background lead (Melice, Yugoslavia) around the guard counter and by increasing the gas pressure in the guard counter from 0.9 to 2atm. Also, an electronic shield consisting of a steel cabinet containing the counters, the preamplifiers, and the lead shield eliminated background variations caused by electric noise. Before combustion, wood and charcoal were treated with 4°, o HC1 and 4jo NaOH. The counting method is essentially the same as described in R., 1971, v. 13, p. 135-140, using a 1.IL proportional counter at 3atm CH, pressure. Sample descriptions were prepared in collaboration with collectors and subnaitters. The errors quoted correspond to l u varia- Ctio''n h oalff -sliafme.p Dlea tnae ta rceo nunotti ncgo rrreactete da nfdo r dioso ntoopti cin fcrlaucdteio nthaeti ounn. cTerhtaei nretyc enint activity of speleothems (dripstones) is assumed to be 85j") of modern samples ; therefore 1305 yr has been subtracted from the radiocarbon age (1\1i_innich and Vogel, 1959).

Radiocarbon dating; Archaeology

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