Radiocarbon measurements in this list were made from Sept. to Dec., 1968. They are based on acetylene counting in an Oeschger-Houtermans-type proportional counter (1 L) at pressure 1 atm. All data are based on duplicated measurements. For calculation of ages, 95% activity of NBS oxalic acid is used as the modern standard and value of 5570 + 30 years is used for the half-life of C14. Dates are expressed in years B.P. (before A.D. 1950). Error corresponds to 1σ deviation of sample net counting rate as well as modern standard and background. Details of procedures are given in previous reports (R., 1968, v. 10, p. 144–148; 1969, v. 11, p. 509–514)

This list includes age measurements carried out from November 1969 to December 1970. All archaeologic and geologic samples come from Italian territory. Laboratory equipment, largely unchanged, has been described (Alessio et al., 1970).

The C14 measurements reported here were made in this laboratory between January 1969 and July 1970. Details of our apparatus, sample preparation, and measuring procedure were described in R., 1968, v. 10, p. 144–148. A change has been made since January 1969: strontium carbonate is reduced to strontium carbide with a mixture of 60g of SrCO3 to 40g of Mg-powder (<200 mesh) instead of 60g of SrCO3 to 50g of Mg-powder (<50 mesh).

The Rehovot Radiocarbon Laboratory was established in 1968, as an extension of a low-level tritium laboratory, which has been in operation many years. Intended to be a supporting facility in geohydrological studies, the laboratory now offers general services in carbon dating.

The dating equipment in the Palaeoecology Laboratory remains essentially as described in R., 1970, v. 12, p. 285–290, and the operating conditions as described in R., 1970, v. 12, p. 291–297. Small samples, however, have been counted at a filling pressure equivalent to 152 cm Hg at 20°C. Charcoal samples pretreated by nitration have been treated as described in R., 1970, v. 12, p. 285–290. Other charcoal samples have been pretreated using the following technique developed by P. Q. Dresser: samples are washed in 5% sodium hydroxide; this is followed by treatment in a solution composed of 8% potassium permanganate and 10% sulphuric acid, at 80°C for 20 mins, to remove residual rootlets and organic matter. Unless specifically stated, the samples have been collected by the authors and other members of the Laboratory: M. G. L. Baillie, P. Q. Dresser, Adelaide Goddard, and I. Goddard. Where a sample has been collected for a specific research project the collector's initials are given. Routine operation of the dating apparatus has been carried out by Mrs. Marilyn Carse and Mrs. Florence Qua to whom we are much indebted.

The following list of dates was compiled since 1967 (R., 1967, v. 9, p. 382-386). Procedures of measurements are essentially unchanged from those reported previously (R., 1964, v. 6, p. 31-36; 1966, v. 8, p. 423-429). The only major change in procedure is that the practice adopted in previous date lists of widening the errors due to fluctuations in C14 content of the exchange reservoir has been discontinued. This leaves the users free to apply the necessary corrections as they become available, e.g., Stuiver and Suess (1966) and Ralph and Michael (1969). The two gas proportional counters were rebuilt in 1968. It was found that outgassing the polytetrafluoroethylene insulators at 100°C under vacuum for 48 hours prior to reassembling the counters considerably hastened attainment of stable operating conditions.

Measurements have continued with the same proportional counter system, the same procedure in sample pretreatment, methane preparation and measurement, and the same age calculation using a half-life of 5568 ± 30 yr as described previously (R., 1970, v. 12, p. 298–318).

The C14 measurements reported here were made in this laboratory between July 1969 and September 1970. The dating system consists of a 0.55 L copper-walled proportional counter (adapted from östlund and Engstrand, 1963, constructed by Outokumpu Oy, Research Lab., Tapiola, Finland) surrounded by a lead cylinder, 1.5 cm thick, placed within an anticoincidence meson detector. The system is encased in selected lead 1.5 cm thick, 7 cm of paraffin wax with ca. 10% boric acid and ca. 20 cm iron. Counter gas is CO2 with which the counter is filled to 228.6 m Hg at a detector temperature of 20°C. Background is 1.50 cpm and net contemporary value is ca. 10.0 cmp.

The C14 dates given below are in years b.p. calculated on the basis of τ1/2 = 5568 years. For converting to a.d./b.c scale, 1950 was used as reference year. Ninety-five per cent activity of NBS oxalic acid was used as a modern standard.

The routine processing and measurement of samples in our Radiocarbon Laboratory began early in 1970 following a one-year testing period during which standard samples (anthracite and NBS oxalic acid) as well as samples of known age were prepared and measured. Our system is based on the studies of de Vries and Barendsen (1953), Fairhall et al. (1961) and Olson and Nickoloff (1965). However, several modifications of the cited methods were introduced and are briefly discussed below. A detailed description of the whole system will be published elsewhere (Srdoč et al., 1970).

The dating equipment and operating conditions remain essentially as previously described. All samples in this list have been counted at a filling pressure equivalent to 152 cm Hg at 20°C. The proportional counter has recently been re-wired, resulting in a lowering of the operating voltage. Electron-microscopic examination of the old counter wire showed considerable thickening due to the accumulation of fine dust particles. A filter is being installed in the filling line to minimize this effect. Pretreatments are as given in previous date lists unless otherwise stated.

The Geochronology Laboratory of the University of Georgia was established in the fall of 1969. The laboratory is housed in the basement of the Geology Building and is under the direction of the General Research Department. Radiocarbon dating facilities are the first to be developed in the laboratory. Other methods will be employed to date a wide spectrum of samples over extensive age ranges. Facilities of the laboratory are also available to colleges, universities, and institutions for teaching and research.

Radiocarbon dates obtained since December, 1969, are summarized here. Procedures and equipment have been described previously (R., 1966, v. 8, p. 522). Wood, charcoal, and peat samples are pretreated with dilute NaOH and dilute H3PO4 before conversion to the counting gas, methane; marls and lake cores are treated with acid only. Very calcareous materials are treated with HCl instead of H3PO4.