In 1969, at the Nobel Symposium on “Radiocarbon Variations and Absolute Chronology” in Uppsala, a curve was presented that illustrated the functional dependence of measured conventional radiocarbon dates on true historical ages of wood samples (Suess, 1971). The curve was derived from the results of La Jolla measurements of radiocarbon in bristlecone pine wood dendrochronologically dated by and obtained from Professor C W Ferguson of the University of Arizona (Ferguson, 1968). The curve was intended to be adequate for deriving calibrated radiocarbon dates and also for allowing fairly reliable estimates of the accuracy of the absolute dates obtained in this manner. The basis for the validity of this calibration is the well known fact that, for all practical purposes, wood samples that had grown at the same time show the same radiocarbon content. However, the reverse is not always true: Wood samples showing the same radiocarbon content do not necessarily have the same age because of the windings and steps of the curve (Stuiver and Suess, 1966).

This list includes most of the measurements made in 1975 and 1976. Results lower than Ly-1000 are old measurements obtained with counters previously described, especially in R, 1973, v 15, p 134, when the laboratory was in the basement of the Nuclear Physics Institute. At the end of 1974 all the apparatus was transferred to a specially designed building with an isolated counting room overlain by 4m non-radioactive earth.

The Radiocarbon Laboratory began operation in mid-1972, using benzene synthesis. The equipment for the laboratory was obtained under a National Science Foundation Grant*. Basic equipment consists of a benzene synthesizer (Alford Instrument Co) and a liquid scintillation counter (Picker-Nuclear 220). The equipment is essentially identical with that of Noakes and Brandau (1971). Counting efficiency and background rates are also similar; ca 70% efficiency with a 4 to 5cpm background for 5ml benzene samples. Benzene synthesis is standard with sample combustion in pure oxygen under reduced pressure. The original synthesis system has been modified to permit simultaneous processing of more than one sample.

This list includes results of measurements made during 1973-1974 and 1975 in the Natural Radiocarbon Laboratory of the Centre de Recherches Radiogéologiques de Nancy (CRR).

This list includes ages measured from August 1974 to May 1976 using the benzene scintillation method. All archaeologic and geologic samples except Sahara Libico series, come from Italian territory. These datings were carried out partly with the liquid scintillation counter previously described (Alessio et al, 1973) and partly with a new liquid scintillation counter (Alessio et al, 1976b). Vials, 4.5ml in volume, described in Alessio et al, 1973. Mixture consists of 3.5ml of benzene from sample and 1ml of commercial liquid scintillator NE 216. The characteristics of new counter are: background 2.90 cpm and figure of merit

This list includes dates measured from July 1975 to December 1976 with CO2 proportional counters. All archaeologic and geologic samples except for Turkey and Sistan series come from Italian territory. Laboratory equipment, largely unchanged but expanded and technically improved, has been previously described (Alessio et al, 1970b, 1976).

Most dates in this list were obtained between 1972 and 1976. Treatment of samples has remained essentially the same as described previously (R, 1975, p 364).

The following dates are a partial list of geologic samples dated since December 1976. The method used is described by (Stipp et al, 1976). Ages were calculated using a half-life of 5568 years. Errors reported are one standard deviation and include only the counting errors on the unknown sample, background and modern standard. There have been no corrections made on these dates. Sample descriptions and comments were written, based on information supplied by the submitters.

This list contains the results of some measurements made between 1965 and 1973. Samples are counted in the form of acetylene gas, as previously, and ages computed on the basis of the Libby half-life, 5568 ± 30 years. The dates have not been corrected for fractionation by a δ13C measurement. The error listed, always larger than the one-sigma statistical counting error commonly used, takes into account possible fractionation in the laboratory and in nature and the variability experienced with replicate samples. We wish to thank Charles Oman for his technical assistance.

Procedures and equipment of the laboratory have been described in previous date lists. Except as otherwise indicated, 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.