Thermoluminescence dating sediments
Two forms of luminescence dating are used by archaeologists to date events in the past: thermoluminescence (TL) or thermally stimulated luminescence (TSL), which measures energy emitted after an object has been exposed to temperatures between 400 and 500°C; and optically stimulated luminescence (OSL), which measures energy emitted after an object has been exposed to daylight.
To put it simply, certain minerals (quartz, feldspar, and calcite), store energy from the sun at a known rate.
The trapped charge accumulates over time at a rate determined by the amount of background radiation at the location where the sample was buried.
Stimulating these mineral grains using either light (blue or green for OSL; infrared for IRSL) or heat (for TL) causes a luminescence signal to be emitted as the stored unstable electron energy is released, the intensity of which varies depending on the amount of radiation absorbed during burial and specific properties of the mineral.
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Several factors that apparently have influeneed negatively the accuracy of other results are: use of ultraviolet TL emissions; use of the regeneration TL procedures for feldspar-bearing samples: use of a single preheating procedure; and use of a peak-integration procedure rather than an equivalent-dose plateau test.These slowly decay over time and the ionizing radiation they produce is absorbed by mineral grains in the sediments such as quartz and potassium feldspar.The radiation causes charge to remain within the grains in structurally unstable "electron traps".This energy is lodged in the imperfect lattices of the mineral's crystals.Heating these crystals (such as when a pottery vessel is fired or when rocks are heated) empties the stored energy, after which time the mineral begins absorbing energy again.
Search for thermoluminescence dating sediments:
For several years attempts have been made to establish reliable procedures for thermoluminescence (TL) dating of sediments older than ≈100 ka.