This date list contains the results of 14C determinations of archaeologic samples from Spain and Portugal obtained at the Laboratory mostly from 1983 to July 1986. Preparation and measurements were made in the same manner as previously reported (R, 1982, v 24, no. 2, p 217–221; R, 1985, v 27, no. 3, p 610–615; R, v 28, no. 3, p 1200–1205).

Measurements have continued with the same proportional counter system, pretreatment procedure, methane preparation and measurement, and calculation, as described previously (R, 1970, v 12, no. 1, p 298–318). Uncertainties quoted are single standard deviations. No 13C/12C ratios were measured. Sample descriptions have been prepared in cooperation with submitters. Some dates have been calibrated using the correction tables of Klein et al (1982) and are reported as “cal” ages in the comment.

Graphite in various forms has become the standard target for accelerator 14C dating. Graphite has been made by catalytic graphitization of charcoals (Lowe, 1984). Thin films of graphite have also been produced by thermal cracking (Beukens & Lee, 1981), electric discharge (Andrée et al, 1984; Wand, Gillespie & Hedges, 1984). Vogel et al (1984) pointed out the ease of graphite formation on iron from CO2 and H2 mixtures at ca 600°C. The deposition reactions of carbon from the CO, H2, and CO2 equilibria are well known (Wagman et al, 1945) and well studied. Formation of graphite from CO2 was discussed extensively by Boudouard (1902) and Schenck and Zimmerman (1903), and was known to chemists in France in 1851. We have used a related method, where graphite forms away from the iron, by using a higher temperature, and reduction of CO2 to CO over Zn in the presence of H2 (Jull et al, 1986) as an alternative to the use of Fe alone. The object of this paper is to point out an even simpler graphite preparation system, which eliminates hydrogen. The decomposition reaction of CO (Boudouard, 1902) takes place according to reaction (1).

The following list consists of dates for archaeologic samples mostly measured from June 1984 to June 1985. The dates were obtained by liquid scintillation counting of benzene using the laboratory procedures outlined in previous lists (see, eg, BM-VIII, R, 1976, v 18, p 16). Dates are expressed as suggested by Stuiver and Polach (1977), ie, in 14C years relative to AD 1950, based on the Libby half-life for 14C of 5570 yr, and corrected for isotopic fractionation (δ13C values are given relative to PDB). No corrections have been made for natural 14C variations. The modern reference standards are the NBS oxalic acids (SRM 4990 and RM 49). Errors quoted are the counting error for the sample, combined with an estimate of the errors contributed by the modern and background samples. This estimate includes both counting and non-counting errors, and is computed from differences in the overall count rates observed among the individual backgrounds and moderns. The overall error is given as ± 1 standard deviation (± 1σ). Descriptions, comments, and references to publications are based on information supplied by submitters.

Procedures and equipment used in the University of Wisconsin laboratory have been described in previous date lists. Except as otherwise indicated, wood, charcoal, and peat samples are pretreated with dilute NaOH—NA4P2O7 and dilute H3PO4 before conversion to the counting gas methane; when noted, marls and lake cores are treated with acid only. Very calcareous materials are treated with HCL instead of H3PO4. Pretreatment of bone varies with the condition of the bone sample; solid bone with little deterioration is first cleaned manually and ultrasonically. The bone is treated with 8% HCL for 15 minutes, then dilute NaOH—Na4P2O7 for 3 hours at room temperature, washed until neutral, and the collagen extracted according to Longin (1971). Charred bone is treated with dilute HCL, NaOH—Na4P2O7, and then dilute HCL again.

The results presented in this list include some recently measured samples (1984) but mostly ones from our earlier years of operation which had not been previously published in RADIOCARBON. It is the first of a number of special lists prepared over the last year so that the backlog of unpublished dates of this laboratory will be cleared. The samples are all archaeologic from the United Kingdom most of which have originated from “rescue”-type excavations.

Samples of inshore marine shell species (various taxa, see description below) were collected from controlled excavation of ceramic-bearing strata of two archaeologic sites in the Manu'a Island group, American Samoa. Located on the closely adjacent islands of Ta'u and Ofu (14° 14’ 30” S, 169° 30’ 40” E and 14° 10’ 55” S, 169° 39’ 0” E, respectively), these sites represent human occupation along shorelines undergoing a parallel depositional sequence of calcareous sand dune development and concomitant seaward progradation. Our primary objective was to obtain an initial age estimate for prehistoric ceramics from eastern Samoa. On stylistic and technologic criteria, the ceramics recovered from our excavations can be classified as thick-coarse Polynesian Plainware. Based on previous studies in Western Samoa, Polynesian Plainware represents a terminal phase of prehistoric pottery manufacture in the Samoan Islands, believed to date from ca 200 bc to ad 300 (Green & Davidson, 1974).

This list contains results obtained between 1981 and 1985. Since the first description of the laboratory (Carmi, Noter & Schlesinger, 1971) the following changes were made. Two proportional counters are now used: 1) 0.5L volume, 0.865 ± 0.023 cpm background, 12.830 ± .134 cpm NBS oxalic acid standard (old); 2) 0.25L volume, 0.484 ± 0.023 cpm background, 6.185 ± .123 cpm NBS oxalic acid standard (old). The passive shield has been increased by 2cm of mercury next to the counters. For anticoincidence, a modular, hand-made gas counter is used. The laboratory was transferred to the ground floor of a 7-storey building. Data acquisition and processing are done with a sealer/buffer built at the institute and an IBM PC computer. Samples are filled into the counters and counted for ca 1000min at least twice. The sample preparation method and counter filling pressure have not been changed.

The following radiocarbon date list contains dates of samples from Plitvice Lakes measured since our previous list dealing with tufa from this region (Srdoč et al, 1982). Tufa measurements from the Knin area in S Croatia and some localities in Bosnia are also listed. Age calculations are based on the Libby half-life (5570 ± 30) yr and reported in years before 1950. Reported ages are based on the initial activity of 85% except for lake sediments where calculations of initial activity have been performed. The modern standard is 0.95 of the NBS oxalic acid activity. Sample pretreatment and counting technique are essentially the same as described in R, 1971, v 13, p 135–140, supplemented by new techniques for groundwater processing (R, 1979, v 21, p 131–137). Statistical processing of data has been computerized (Obelić & Planinić, 1977; Obelić, 1980). The errors quoted correspond to 1 σ variation of sample net counting rate and do not include the uncertainty in 14C half-life.

The following radiocarbon date list contains dates of samples measured since our previous list (R, 1984, v 26, no. 3, p 449–460). As before, age calculations are based on the Libby half-life (5570 ± 30) yr and reported in years before 1950. The modern standard is 0.95 of the NBS oxalic acid activity. Sample pretreatment, combustion and counting technique are essentially the same as described in R, 1971, v 13, no. 1, p 135–140, supplemented by new techniques for groundwater processing (R, 1979, v 21, no. 1, p 131–137).

We strongly welcome the investigation by Geyh and Hennig (1986) and agree with their conclusion that the boundaries of the interglacial periods cannot be determined exactly using the methods applied so far in the Heggen cave. However, since we have been engaged for several years in the application of these methods (except 14C), and since the paper gives a very different interpretation of the ESR results from that presented by one of us (Grün, 1985), we feel the need to make some comments on this paper.