M. Járó - L. Költő szerk.: Archaeometrical research in Hungary (Budapest, 1988)
Dating - BENKŐ Lázár: Thermoluminescence dating of Hungarian archaeological sites (potteries, hearths, calcite)
After sieving., the fraction from 0.09 to 0.125 mm was used for the TL measurements. Alternatively, the procedure was complemented with magnetic separatio}! by means of a permanent magnet. In our standard glow-out technique 2 mg portions of quartz were uniformly spread, as fairly loose monolayers, on stainless steel cups. Laboratory irradiations were carried out with a beta irradiator (Daybreak model) containing a strontium source of about 2.10 9 Bq activity. Its calibration was performed with a gamma source at the National Bureau of Standards. In our standard on-plate irradiation procedure, the dose delivered per minute to quartz by the beta source quoted above is 2.49 Gy. For dose-rate measurements mermoluminescence itself was used. In TL dosimetry for radiation protection purposes, a number of phosphors are available which can measure doses as low as 0.01 mGy or less. One of them, synthetic calcium sulphate activated by dysprosium, was selected for measuring the gamma dose*ate from the burial soil and the beta dose-rate from the clay matrix of the pottery. In the case of the soil, a copper capsule of wall thickness 1 mm is sufficient to stop beta particles from reaching the phosphor. After filling the capsule with about 0.1 g of CaS0 4 :Dy it is made watertight and then inserted into the soil in as similar a situation as possible to that from which the pottery fragment was removed. It is preferable to leave the capsule buried for a year in order to even out seasonal fluctuations of dose^ate which are due to variations in water content. In order to measure the beta dose-rate from the clay matrix, the CaS0 4 :Dy phosphor is contained in a polycarbonate tube (internal diameter 1 mm) which is inserted into a small plastic container filled with the powdered sample. By shielding the container |against external radiation, after storage of about a month the TL emitted by the phosphor can accurately be measured. Alpha particles are prevented from reaching the phosphor by the 02 mm thick wall of the tube. By appropriate calibrations with samples of known radioisotope concentrations, the correction factor, which is mostly due to beta attenuation in the wall, was determined (the true dose within the sample is approximately twice the phosphor dose). The beta dose^ate is measured on dry material therefore it is to be corrected for the water content of the sample in burial conditions. Wetness is expressed in terms of the saturation water content (W) and the actual value of Dß is given by n D /3dry p 1 + 1.25WF where the factor of 125 accounts for the higher beta absorption of water relative to that of the sample . F denotes the fraction of saturation to which the average water content corresponds. In this respect, there is a significant uncertainty, hence F = 0.8 ±0.2 is assumed. The annual dose is influenced by radon emanation, too. The escape of the gaseous member of the uranium chain can have a substantial effect on dose-rate and we are limited to rough estimations as far as the emanation extent in the true burial circumstances is concerned. However, in most cases alpha counting proved to be a convenient laboratory approximation. Crushed samples were measured in both sealed and unsealed condition. When precise dating is required, only those samples should be accepted for which the sealed count-rates do not exceed by more than 10% the unsealed ones.
