ALPHA-COUNTING USING SCINTILLATION TECHNIQUES - OBSERVATIONS ON TSAC-CALIBRATION AND GAS-CELL USE

Two aspects of alpha counting using the scintillation technique in the field of luminescence and ESR dating are addressed. The first part of the article concerns the evaluation of the proportion of radon that e manates out of the studied samples. A modified version of the gas-cell developed in the Research Laboratory for Archaeology and the History of Art, Oxford, was used for this purpose. Basically the new cell show s a reduced volume above the ZnS screen. This geometry is intended to hinder thermal convection, which is suspected to be responsible for th e irregular shifts in counting efficiency that are observed with the O xford cell. It is demonstrated that the modified cell can be calibrate d without sources of known emanation, unlike the Oxford cell. The seco nd part of the article deals with the calibration of the Thick Source Alpha Counting technique (TSAC). This is usually achieved by adjusting the threshold of the electronic discriminator, according to certain r ules, by means of standard samples. In the present study, calibration was achieved by comparing the observed count rate to the predicted cou nt rate using a set of archaeological and geological samples of well k nown uranium and thorium contents. The results are discussed. (C) 1997 Elsevier Science Ltd.