"Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing happened."
Winston Churchill
The 14C dating method was invented by Willard Libby (Libby et al., 1946; Andersen et al., 1947), 50 years ago. Since then, two major improvements have sharpened the precision and applicability of this unique instrument:
The atmospheric 14C content during the past ten thousand years is now well established through comparison with dendrochronology (the tree-ring calibration). This allows one to convert 14C measurements into calendar dates, although of varying precision due to the natural 14C variations. It is important, however, that "good" and "bad" dating periods can be well distinguished from the calibration curve.
The development of Accelerator Mass Spectrometry (AMS) increased the efficiency of radiocarbon measurements by a factor of approximately hundred thousand as compared to beta counting. As a result, only milligram amounts of carbon are needed instead of grams, and the measuring time is reduced from several days to less than one hour. This makes it possible to date archaeological objects where little material is available and/or to make systematic measurements with many samples.
The half-life of 14C (t1/2 = 5730 a) is ideally suited to investigate the whole period of civilization of modern man. From a nuclear physics point of view, the length of the half-life is a great gift of nature because it stems from a very rare and large hindrance of the beta decay process. This effect, which is caused by subtleties of the quantum structure of nuclei, slows down the decay by five orders of magnitude as compared to a normal-strength beta decay. The latter would result in a rather useless half-life of only about 20 days.
In principle, 14C dating is straightforward, but in practice many factors have to be carefully evaluated if accurate dates are to emerge. A one-percent uncertainty of the 14C/12C ratio measurement translates into an uncertainty of 83 years (1% of the mean life, independent of age). The experimental goal of VERA is to reduce the measuring uncertainty to approximately half this value. However, a 40-year uncertainty in the measurement may well translate into a much larger uncertainty of the calibrated date due to "wiggles" in the calibration curve as discussed in section 2.2, and due to uncertainties connected to the origin of the specific sample material. As for the calibration process, it is intended to further develop the calibration software from Oxford in collaboration with that laboratory.
The basical layout of the VERA facility is described in section 3.1 and the principle of a 14C measurement with AMS is discussed in this section. VERA can be operated in a fully computer-controlled mode, which will allow one to reduce operational errors, and at the same time have a high sample throughput. In addition to on-line analysis, detailed off-line analysis of the collected data can be performed. Since essentially all machine parameters are stored for each run, good quality control of the measurements is possible.
Considerations for acquiring a stable isotope ratio mass spectrometer system are discussed here. This system is closely connected to the sample preparation. VERA was set up with the intent to overcome the typical bottle neck of AMS facilities, which is the sample preparation. For the current project, a considerable extension of the sample preparation capacity is planned. It is proposed to employ a full-time chemist to implement this program.
The purpose of the 14C dating effort is to establish an improved chronology for various archaeological settings in Austria and Central Europe. Archaeological questions in this context are discussed here. Since the intend is a rather broad survey with many samples to be analysed (~ 1000), a fairly large group of suppliers of samples have been contacted (see table 1). Of course, the reliability of a date depends also on the integrity of the sample. Therefore, only unambiguously identified samples with a clear archaeological context and a well-preserved status (particularly for bones) will be dated.
It is our hope that the initiative started with this project will lead to a considerable improvement in both 14C dating capabilities at VERA and absolute chronologies in a number of interesting archaeological sites throughout Austria and Central Europe.