Beginning in 1955 a C14 dating apparatus was constructed at this University for the purpose of measuring the specific activity of tree rings selected from a specimen of Sequoia wood having 3000 growth rings (Dorn, 1958). The original purpose was to obtain a measure of the half life of C14 by essentially the inverse of C14 dating. For various reasons the project was not completed, and for about a year the apparatus stood idle for lack of financial support. This latter deficiency has now been rectified, at least temporarily, and research with the apparatus has been resumed. Fabrication of a second, 1 L counter is nearing completion.

This paper reports the first ages determined in the C14 Dating Laboratory of the Geological Survey of Canada. The C14 dating program of the Geological Survey is a cooperative project; geologists of the Pleistocene Section assess and select samples for dating, and the Isotope and Nuclear Research Section, under Dr. R. K. Wanless, developed and operates the laboratory and calculates ages. The first part of this paper, devoted to sample preparation, counting procedure, and interlahoratory check dates was prepared by the first author, who built and operates the laboratory. The date list was compiled by the second author from descriptions of samples and interpretations of dates provided by various collectors. Most samples analyzed so far have originated within the Geological Survey.

The following list includes samples dated in the period 1956–1961.

Age calculations are based on a contemporary value equal to 95% of the activity of the NBS oxalic-acid standard, and on a half life for C14 of 5568 ± 30 yr.

The following list presents the dates obtained on a fraction of the total number of measurements made during the year 1961. Those results which do not appear are withheld pending additional information or at the request of our clients.

The C14 Dating Laboratory of the University of Texas has been working on the development of two systems of counting: gas counting with methane, and liquid scintillation counting with benzene. Lack of adequate instrumentation has retarded the work on gas counting, but the liquid scintillation work, supported in part by the Department of Chemistry, finally led to the successful development of a system in which the benzene counting solvent was synthesized from acetylene by pyrolysis (Tamers, Stipp, and Collier, 1961).

The construction of the dating apparatus started in the summer of 1960 and was completed one year later. The laboratory is located on the bottom floor of a three-story concrete-block building which has two thin concrete floors on concrete beams above the shield. The building is underlain by carbonate mud and coral rock. The geographic location is 25° 43.9′ N Lat, 80° 09.8′ W Long and only a few feet above sealevel. We use a proportional-counting tube with an active volume of 1 L, and a total sample volume of 1.30 L, filled with purified CO2 to a pressure of 225 cm Hg (3 atm) at 25°C. The tube is made of copper with brass ends and quartz insulators. The shielding consists of 20 cm of iron, 10 cm of paraffin with boric acid, 2.5 cm of selected lead (Östlund, 1961), and cosmic ray guard counters. The room is air-conditioned but no additional precautions have been taken to exclude outdoor dust.

The dates and activity measurements given below have been obtained during the year 1961, and have been made with CO2 at 3 atmospheres pressure in a proportional gas counter as described in previous contributions from this laboratory.

The third series of C14 measurements made at the University of Saskatchewan is reported in the present list. The equipment and methods have been described previously (Saskatchewan II). The modern reference standard was 0.950 times the activity of the NBS oxalic-acid standard. The activity of the wood standard used previously corresponded to 0.955 ± 0.009 of the NBS standard, so that no corrections are required to the previous date lists to bring them into line.

The C14-laboratory at the Geological Survey of Finland was started in October 1960 in order to determine ages of Quaternary objects. Only 11 samples that have been measured are ready to be published. Most samples in the following list have been measured many times in order to control the stability of the system and to make all necessary corrections. The C14-system includes two CO2-filled proportional counters. Until now the measurements have used only the first counter system. The second one is now ready for dating.

Natural C14 measurements have been performed at Gakushuin University since 1959, using a proportional counter of 400 ml (Kigoshi and Tomikura, 1960). The counter presently in service is made of copper tubing and has an effective volume of 900 ml. Acetylene gas is used as counting gas at pressure 600–760 mmHg and prepared in the same way as in the case of 400 ml counter. The counter is shielded by iron sheets of 23-cm thickness and by anti-coincidence with a multianode propane-flow proportional counter of Houterman's type (Houtermans, 1958). A background of 5.6 counts/min has been attained with this counter arrangement. The modern carbon sample filled at 0°C and 760 mmHg shows an activity of 11.8 counts/min. The samples with code numbers greater than GaK-60 were measured by this counter.

The following list covers the samples measured at the Louvain C14 dating laboratory during a period from May to December 1961.

The following list covers the measurements in our institute until the end of 1960.

The measurements reported in this list have been made since the Radiocarbon Dating Laboratory at the Institute of Geophysics, UCLA became operational in August 1961. CO2 proportional counting was used for all measurements in an 7 · 5-L counter at 1 atm pressure. Dates have been calculated on the basis of the C14 half life of 5568 ± 30 yr, and 95% of NBS oxalic acid as modern standard. It is planned to discuss the half life in the light of the newer measurements at a conference in 1962. Prior to general agreement as to the new best figure we propose that all dates continue to be calculated on the old basis. Samples have been carefully inspected, cleaned, picked free of rootlets, and pretreated with HCl when necessary.

This paper is a direct continuation of the third dating list (Stockholm III), and the entire technique is virtually unchanged, using one 0.5–1 and one 1.0.1 3 atm CO2 proportional counter. Ages are calculated according to the recommendation given in the introduction of this book, and δC13 has been measured for unknown samples and for the different CO2 preparations of the NBS oxalic-acid standard. Since the numerical relationship between the C14 activity of our old oak standard and that of NBS was valid for a δC13 value of almost exactly −19 for the NBS preparation in question, it still holds true that all dates given in Stockholm I, II and III can be converted to the new scale by subtracting 55 yr. The NBS preparation St-532 measured by Craig (1961) having a δC13 value of −17.2 is only one of several preparations with values between −17 and −20. Age figures are given in C14 yr before A.D. 1950; the half life for C14 is taken as 5568 ± 30 yr.

The results described herein are measurements performed in 1961. Sample preparation and conversion into acetylene have been described (Wendt, Schneekloth and Budde, 1962). In calculating errors we did not follow the procedure used in our Date List I, where only the standard deviations of counting rates were used. The errors attached to the dates listed below include systematic errors due to sample preparation and small changes in the counting characteristics of sample, background, and standard counting gas.

In conformance with the request of the editors, ages in this date list have been calculated with the Libby half life value, 5568 ± 30 yr. We should like to mention, however, that the “effective” and, possibly, the true value may differ from this by several hundred years (see discussion by Kohler and Ralph, 1961). The measurements of samples of known age indicate that the “effective” half life value is close to 5800 yr, except for specific recent periods.

This date list covers most of the datings done during the period January 1960 to December 1961.

The following is a list of C14 dates obtained since the preparation of the manuscript for publication of Michigan Radiocarbon Dates VI in December 1960. The method of measurement and treatment of data are the same as described in the introduction to Michigan lists III and IV. Since the time of publication of list VI, a full description of the counting technique and equipment has been published (Crane, 1961a, b).

Since the publication of the last list of C14 measurements (La Jolla I), covering the period from mid-1957 through 1959, the La Jolla Radiocarbon Laboratory has continued to use essentially the same technique. In the summer of 1961 a second Oeschger-Houtermans counter (Houtermans and Oeschger, 1958), purchased from Manufacture Belge de Campes et de Matériel Electronique, S. A., was installed. It has a somewhat higher background (3.1 counts/min at a filling pressure of 880 mm) than the counter obtained from Bern—a point of little significance in the measurements herein reported. Of the tests included in this report only those following LJ-380 were run with the new counter; the others, with the Bern counter.

Radiocarbon-age measurements reported here were made by the carbon dioxide gas-proportional counting method since conversion of the laboratory from the solid-carbon method. Assembly of the shield and construction of the glass system was accomplished during the summer of 1959. By January 1960, shield, anticoincidence ring, counters and electronics were set up and in operation. The first year of operation was occupied with calibration, comparison of dating with other C14 laboratories, and the repeating of many of the analyses previously made by the solid-carbon method. Special attention was given to dates open to question from an archaeologic point of view.