Dating by thermoluminescence
Some clays are hardly thermoluminescent at all; some may not have a straight-line relationship between dose and TL; spurious luminescence due to chemical or pressure effects may mask the radiation-induced TL; occasionally, a condition called "anomalous fading", where part of the TL is unstable, may lessen the accuracy of the dose measurement.
Generally speaking, when a sample is drilled and there is no information available about the burial environment, one may expect up to 40 per cent uncertainty.
Some of these are quite easy to detect; some quite difficult.
For example figures, normally modeled, may be carved out of brick or assembled out of fragments.
By comparing this light output with that produced by known doses of radiation, the amount of radiation absorbed by the material may be found.
Most mineral materials, including the constituents of pottery, have the property of thermoluminescence (TL), where part of the energy from radioactive decay in and around the mineral is stored (in the form of trapped electrons) and later released as light upon strong heating (as the electrons are detrapped and combine with lattice ions).
The clay cores from lost wax metal castings may readily be tested.
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In all, close to two dozen physical quantities must be accurately measured to establish the relationship between doses of different kinds of radiation and light output, and to compute dose rate.
This radiation may in some cases contribute over half the total dose.
Finally, one has to make the measurements regardless of whether the TL of the clay is well-behaved or not.