This radiocarbon laboratory was established by a grant from Brooklyn College to support the work of its archaeologists and geologists. The method of dating is that of benzene synthesis and liquid-scintillation counting developed by a number of investigators (Noakes et al, 1965; Polach and Stipp, 1967; Tamers, 1975). This list includes nearly all samples processed so far, most of which were done since September 1975.

The 14C dates listed in this report on archaeologic and geologic samples were obtained mainly from 1969 to 1974. Pretreatment of wood charcoal and carbonized fossil soil by boiling in acid, alkali, and acid, again, is standard procedure. The method employed is liquid scintillation counting of synthesized benzene using the basic techniques described by Arslanov and Gromova (1968) converting sample → Li2C2 → C2H2 → C6H6 with an overall yield to ca 90%. A vanadium-alumina catalyst is used at reduced temperature for the acetylene to benzene conversion. Anthracite coal was used for the dead carbon run.

Radiocarbon dating of many types of samples has continued at the La Jolla Radiocarbon Laboratory since the last date list was published (Bien and Pandolfi, 1972). Since the 1969 relocation of the laboratory to its present location on Mt Soledad, at least 5 low-level 14C systems have generally been in operation. The laboratory has continued to employ acetylene gas proportional counting. Samples were usually measured for 2 to 3 days in each of 2 different detectors. The properties of the 5 counters used in the measurements of samples are as follows (background and net standard counts per minute, respectively, with acetylene of 900mmHg pressure are given in parentheses): 1) Bern counter: Oeschger-type counter-guard ring unit with 1.7L sensitive center volume (2.1, 21.5), 2) MBLE counter: Oeschger-type counter-guard ring unit with 1.6L center volume (1.3, 17.4), 3) 1L counter with separate Q-gas flow guard ring (4.2, 12.9), 4) 0.4L counter with separate guard ring (1.2, 4.2), and 0.1L counter with separate guard ring (0.7, 1.2).

Most of the 14C measurements reported here were made between October 74 and March 76. The usual procedures and methods of sample preparation are those described in R, 1964, v 6, p 194-196. The electronic apparatus was constructed by J Galliot from results of studies on background of proportional counters (Delibrias & Rapaire, 1967) and was described briefly in R, 1966, v 8, p 286-291.

The 14C dates given below are continued from our previous list (R, 1974, v 16, p 331-357), and results obtained mainly during 1972-73 are described. A 2.7L stainless steel counter and a 3.3L copper counter are used as previously, yielding background counting rates of 3.9 and 5.6cpm, respectively, when filled with dead CO2 at ca 1.7atm. Dates have been calculated on the basis of the 14C half-life of 5568 ± 30 yr and 95% of NBS oxalic acid is modern standard. Errors (± 1σ) include standard deviations for sample counts, background and modern standard, that of half-life, and, also, effective standard deviations for reading of filling pressure and temperature. No correction has been made for any of the samples in this list.

The present list reports 14C measurements made in our laboratory from December 1972 to December 1973.

The following list contains measurements made during the period 1972-5 which have not been previously published and which form part of a research project on marine shell dating (Gillespie, 1975). These sets of samples were measured to determine 1) “apparent age” of marine shells coll alive from Australian coastal waters before the advent of large-scale nuclear weapons testing, 2) the possibility of using post 1950 Australian marine shells as a modern reference, 3) “apparent age” of Australian marine shells in the past as shown by comparisons between stratigraphically equivalent charcoal and marine shell samples.

The following list includes samples dated in 1975. The measurement of 14C activity was performed with 1-channel and 2-channel scintillation devices. Special attention was paid to the decrease of the background. The effectiveness of the measurement is ca 50% (Punning, Rajamäe, 1975). The “enriched standard” (Alekseejev et al, 1971) has been used as a contemporary reference standard of modern carbon. Age calculations are based on the 14C half-life of 5568 ± 30 yr, with 1950 as the standard year of reference. All samples are calculated to ± 1σ with respect to sample, standard and background after counting times of at least 2800 minutes. 13C/12C measurements and corrections have not been made for these samples.

The following radiocarbon measurements are a partial list of projects and samples dated since January 1975. The technique used is described in R, v 16, pp 402-408 and R, v 18, pp 210-220. Dates are calculated using 14C half-life of 5568 yr and errors are reported as one-standard deviation.

Procedures and equipment of the laboratory have been described in previous date lists. 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 samples are treated with dilute HCl instead of H3PO4.

A radiocarbon dating system has been established at the Department of Geology and Geophysics, Yale University. Liquid-scintillation counting of benzene described by Noakes et al (1965) and Polach and Stipp (1967) is used. The operation of the original Yale Radiocarbon Laboratory, based on counting CO2 gas, was suspended in 1969. The present facility is operated as part of the geochemical laboratories of the Department of Geology and Geophysics. The operation is small, geared to solving geochemical problems, through the use of radiocarbon as a dating tool and as a natural tracer in combination with other geochemical parameters. The facility will collaborate on significant archaeologic and geologic problems. However, it will not be a facility to which samples are submitted routinely. We believe that commercial facilities and other laboratories dedicated to such kinds of operation are better suited to handling such diversity and volume of samples.