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Most excited electrons will soon recombine with lattice ions, but some will be trapped, storing part of the energy of the radiation in the form of trapped electric charge (Figure 1).Depending on the depth of the traps (the energy required to free an electron from them) the storage time of trapped electrons will vary as some traps are sufficiently deep to store charge for hundreds of thousands of years.Often the gamma radiation field at the position of the sample material is measured, or it may be calculated from the alpha radioactivity and potassium content of the sample environment, and the cosmic ray dose is added in.Once all components of the radiation field are determined, the accumulated dose from the thermoluminescence measurements is divided by the dose accumulating each year, to obtain the years since the zeroing event.Where there is a dip (a so-called "electron trap"), a free electron may be attracted and trapped.The flux of ionizing radiation—both from cosmic radiation and from natural radioactivity—excites electrons from atoms in the crystal lattice into the conduction band where they can move freely.An example of this can be seen in Rink and Bartoll, 2005.Thermoluminescence dating was modified for use as a passive sand migration analysis tool by Keizars, et al., 2008 (Figure 3), demonstrating the direct consequences resulting from the improper replenishment of starving beaches using fine sands, as well as providing a passive method of policing sand replenishment and observing riverine or other sand inputs along shorelines (Figure 4).

Release date: Caves are important, yet often fragile, natural subterranean environments.

Some of the most impressive and pristine are those not generally accessible to the general public.

This stamp issue presents four incredible and varied caves from around Australia.

Caves not only house minerals and speleothems, but also often provide a home for rare fauna and ancient fossil deposits.

Australia is home to many spectacular and highly significant caves.

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