Thermal luminescence dating
After deposition of the grains and burial under new sediment, their latent luminescence signal accumulates again because they absorb the natural ionising radiation that is emitted by the surrounding sediment. The age that is determined corresponds to the time span between the removal of the luminescence signal by sunlight just before deposition and the removal of the newly accumulated palaeodose by thermal or optical stimulation in the laboratory.Stimulation by heat is called thermoluminescence (TL) and stimulation by light, optical stimulated luminescence (OSL). The clay core of bronze sculptures made by lost wax casting can also be tested.Different materials vary considerably in their suitability for the technique, depending on several factors.Structural defects in the lattice (vacancies, interstitial atoms, and substitutional impurities) create localized charge deficits, which act as traps T for the conduction electrons.Most electrons recombine or are briefly trapped in very shallow traps, but a few are trapped at deep traps and remain there over geological time-scales (1-1000 Ma).
Ideally this is assessed by measurements made at the precise findspot over a long period.Rising with the sun I slide out of our tent feet first, past the sailcloth ‘Ratbags’ containing all our (present) worldly goods.At the far end of the campsite stand three women, calling at us. For artworks, it may be sufficient to confirm whether a piece is broadly ancient or modern (that is, authentic or a fake), and this may be possible even if a precise date cannot be estimated.Trapping: Upon exposure to nuclear radiation, some bound electrons of the atoms making up a mineral's lattice are detached from their parent nuclei and become freely mobile: they are said to enter the conduction band.