Isochron methods for luminescence dating in archaeology
This work aims to contribute to the solution of a problem relevant to archaeology and microdosimetry, namely the TL dating of destratified archaeological ceramics. It is apparent that museums hold a large body of archaeological material excavated from important sites during the early part of this century. Absolute dating of this corpus of material would be extremely valuable to archaeology in allowing historic hypotheses to be tested. The background to this problem has been presented within the context of the historical development of thermoluminescence dating and of dosimetry concepts. A critical review of previously proposed strategies for dating material from unknown gamma contexts is presented, and then a general model using an isochron approach is introduced. The isochron model is then developed explicitly and theoretical simulation is used to explore different microdosimetric systems. Two main isochron solutions have been identified, the grain size (or alpha-beta attenuation) and alpha efficiency isochrons. An experimental approach was designed, to evaluate the validity of the grain size isochron predictions, using model matrices. Isochron behaviour was clearly observed in both cases. The first system, based on microcline feldspar grains in a high dose rate matrix, produced an age estimate consistent with the known age. The second experiment, using fluorite grains in a lower dose rate matrix, produced a highly coherent data set. However, the age estimate obtained was greater than the expected value by a factor of approximately 3. The possible reasons for this are discussed in detail. A brief experiment carried out subsequently on duplicate portion of this matrix gave results that are consistent with predicted values. Thus, it would appear that the original experimental design and method were valid and that the isochron approach does indeed deserve further investigation.