Thermoluminescence dating pottery
When pottery gets covered in the ground, radiation from the earth starts to energize (excite) the electrons of these crystalline materials, putting them into “trap states.” This is a measure of the radiation dose.The longer the pottery is in the ground, the more radiation dose it will absorb, causing more electrons to be excited into trap states.By comparing the glow-curves we can calculate the dose of radiation absorbed by the piece during its lifetime.Radioactive measurements on the clay tells us how much radiation the piece is receiving each year.At this point, the method seems to be a straightforward concept.However, problems arise from assuming a uniform radiation dose rate over any significant period of time and assuming that the TMRD resulted from the object or artifact being in a strictly constrained environment identical to that in which it was found.
The samples are irradiated in the laboratory with a known radiation dose and heated to produce another glow-curve.When we receive your sample we must first prepare it for measurement.Powder samples (from pottery and bronze cores) are mixed with acetone and allowed to settle, so that fine grains, approximately 1/100mm. These grains are deposited and dried onto aluminium discs (for fine-grain analysis) or rhodium (for pre-dose analysis).For both pieces: curve (a) is the TL emitted by a sample of powder taken from the object, curve (b) is a laboratory induced glow-curve curve (c) is the background.The ancient piece : (a) is way above the background (c), and approximately midway between background and (b) The modern piece : (a) is only just above the background (c) and way below (b) Porcelain and certain other types of clay cannot be tested using the fine-grain method. The TL reader is programmed to measure changes in the 110C peak of quartz (the pre-dose peak) in the clay.