The dates detailed below are based on measurements made from September 1962 to August 1964. Work was often seriously interrupted due to difficulties with electronic equipment and also, from the late summer of 1963, high levels of tritium in the local water supplies used in the synthesis of acetylene (from nuclear weapons tests) made it difficult to obtain accurate measurements with acetylene as a filling gas for the proportional counter. The gas preparation equipment was therefore modified for the preparation of high purity CO2, and from Sample BM-165 onwards, the proportional counter was operated with CO2 as the filling gas at a pressure of 210 cm Hg at 22°C. instead of 140 cm Hg pressure of acetylene at 22°C. as reported previously (British Museum I). Background and net modern count rates under these conditions are 3.59 c.p.m. and 8.35 c.p.m., respectively. (In practice these values are taken as the rolling mean of the past 20 weeks’ measurements and are very constant.) The calculations of age are based on the half-life of 5570 yr and error terms are widened to include contributions of ± 80 yr for possible isotopic fractionation effects and ± 100 yr for de Vries-effects. Safeguards against inaccuracies are as described previously (British Museum I).

The laboratory started dating in 1966 using liquid scintillation techniques. Considerable effort has been expended on improvements in both sample preparation and detection (Pietig and Scharpenseel, 1964 and 1966). Yields now approach 100% and 4 to 6 samples are completed each week. A solution of 3 cc synthesized benzene and 1 cc “dead” commercial toluene is employed for ordinary measurements. Toluene contains PPO and POPOP scintillators that give final concentrations of 0.4% and 0.01%, respectively, when diluted with sample benzene. The counting arrangement with normal shielding gives a net modern count rate of 25.6 cpm (78% efficiency) with a background of 9.7 cpm. A special counter equipped with 5 cm mercury and 10 cm lead shielding as well as an anti-coincidence “umbrella” of polystilbeneplastic scintillator has considerably better characteristics. In addition to reduced background, samples as large as 100 cc can be accommodated. The exceptional performance obtained here is presently reserved for natural radioactivity measurements, such as T-3 and C1–36.

The development of a C14 laboratory within the physical laboratory of the “Institut royal du Patrimoine artistique” was begun by Dr. I. Elskens and D. Gausset (A.I. Br.).

The electronic apparatus was delivered in 1963 and routine counting on gas of petrochemical origin began in 1964. By December 1965, methane gas was prepared from pure commercial CO2 and, in February 1966, the first test samples were burnt.

Plans for a radiocarbon dating laboratory at the University of Lund were initiated by Tage Nilsson and Holger Arbman in 1962. Work was begun in 1964 and at the end of 1965 most of the dating equipment was installed. Dating began in 1966 after careful testing of counting electronics and counters.

The dating system has two 1-L copper-walled proportional counters of Östlund-Engstrand construction (for details see Stockholm V. p. 204, Fig. 1) surrounded by 2.5 cm of selected lead, followed by a ring of 23 cosmic-ray Geiger counters (model HZ-100, Zentralwerkstatt Göttingen). On all sides are at least 20 cm of iron. Above and on both long sides of the counters are 10 cm of paraffin wax with about 12% boric acid between the iron layers.

The following list comprises a selected number of measurements made during 1966–67 with CH4 at 3 atm pressure in a 0.6 L proportional gas-counter as previously described. The B.P. ages are based upon a.d. 1950 and are calculated with a half-life of 5570 yr. The quoted error consists of experimental standard deviation including the counting variations of the unknown sample, the modern standard, and the background.

The following is a list of dates obtained since the compilation of List XI in December 1965. The method is essentially the same as described in that list. Two CO2-CS2 Geiger counter systems were used. Equipment and counting techniques have been described elsewhere (Crane, 1961). Dates and estimates of error in this list follow the practice recommended by the International Radiocarbon Dating Conferences of 1962 and 1965, in that (a) dates are computed on the basis of the Libby half-life, 5570 yr, (b) A.D. 1950 is used as the zero of the age scale, and (c) the errors quoted are the standard deviations obtained from the numbers of counts only. In previous Michigan date lists up to and including VII, we have quoted errors at least twice as great as the statistical errors of counting, to take account of other errors in the over-all process. If the reader wishes to obtain a standard deviation figure which will allow ample room for the many sources of error in the dating process, we suggest doubling the figures that are given in this list.

We wish to acknowledge the help of Patricia Dahlstrom in preparing chemical samples and David M. Griffin and Linda B. Halsey in preparing the descriptions.

The following list comprises measurements made since those reported in NPL IV.

No changes have been made in measurement technique or in the method of calculating results

This paper is a list of the first results of age determinations made at the Centre de Recherches Radiogéologiques de Nancy (CRR). The Center is the result of a convention between the Commissariat à l'Energie Atomique (CEA) and the University of Nancy. It is part of a group of research laboratories of Earth Sciences headed by Prof. M. Roubault.

The following list includes samples dated between 1956 and 1961. Wood dating from A.D. 1850 ± 10 yr is used as a contemporary reference standard. Background sample is synthesized from anthracite. All radiocarbon dates were calculated with the hall-life of C14 being equal to 5568 ± 30 yr. All dates are calculated from the year 1950.

The C14 dates presented here were obtained by counting methane, using the technique described earlier (Agrawal et al., 1965a). In accordance with the decision of the Sixth Pullman Conference (Internat. Gonf., Pullman, 1965) and the editors’ advice we continue to give dates based on τ 1/2 = 5568 years. For converting dates to A.D./B.C. scale, 1950 has been used as reference year. Ninety-five per cent activity of N.B.S. oxalic acid has been used as modern standard.

The University of Tokyo Carbon Dating Laboratory was established to meet the requirements for dating materials from various fields of science at the university. Installation and testing of the apparatus as well as routine assays have been carried out with counsel of Dr. Nobufusa Saito, Professor of Chemistry, and Dr. Yozo Nogami, Professor of Physics, the University of Tokyo. Management of the laboratory is undertaken by the Carbon Dating Committee of he University of Tokyo. The laboratory has actually been working for a year. This article reports the radiocarbon age measurements made from September 1966 to July 1967, together with a brief description of the measuring system.

The measurements reported have been carried out during the first half of 1967 in the Isotope Laboratory of the Institute of Geophysics and Planetary Physics as a continuation of the UCLA date lists I through VI. Samples were analyzed as CO2-gas at close to one atm in a 7.5 L proportional counter with 3 energy channels described earlier. Radiocarbon ages have been calculated for uniformity on the basis of a 5568-yr half-life as was recommended by the Sixth International C14 and H3 Dating Conference, June 1965, in Pullman, Washington. The standard for the contemporary biosphere remains as 95% of the count rate of NBS oxalic acid for radiocarbon laboratories. Background determinations have been based on CO2 obtained from marble. The error listed is always at least a 1σ statistical counting error. In critical cases C13/C12 isotope ratio measurements were made to correct the dates for fractionation. All samples were subjected to accepted NaOH and/or HCl pretreatments depending on the individual case as a minimum to exclude contamination. The annual curve for the atmospheric C14 content at China Lake, California, will be published in the next date list.

Radiocarbon dates obtained at the University of Wisconsin since November, 1966, are summarized in this report. The procedures followed and equipment used have been described previously (Wisconsin II).