Thermoluminescence

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Figure 1: Three stages of thermoluminescence as outlined by Aitken (1985, 1998) and applied to a quartz grain (Keizars, 2008b).
Figure 1: Three stages of thermoluminescence as outlined by Aitken (1985, 1998) and applied to a quartz grain (Keizars, 2008b).
Figure 2: The process of recharging and discharging thermoluminescent signal, as applied to beach sands. (modified from Aitken, 1998; Keizars, 2008).
Figure 2: The process of recharging and discharging thermoluminescent signal, as applied to beach sands. (modified from Aitken, 1998; Keizars, 2008).
Figure 3: Thermoluminescence signature lost during migration of two sand grain sizes (Keizars, 2008).
Figure 3: Thermoluminescence signature lost during migration of two sand grain sizes (Keizars, 2008).
Figure 4: Illustrated method of passively monitoring sand input (Keizars, 2003).
Figure 4: Illustrated method of passively monitoring sand input (Keizars, 2003).

Some mineral substances such as fluorite store energy when exposed to ultraviolet or other ionising radiation. This energy is released in the form of light when the mineral is heated; the phenomenon is distinct from that of black body radiation.

The amount of light given off is proportional to the dose of radiation received. In thermoluminescence dating, this can be used to date buried objects that have been heated in the past (eg pottery) since the dose received from radioactive elements in the soil, cosmic rays etc is proportional to age. This phenomenon has been used for Thermoluminescent dosimeters, to measure the radiation dose received by a chip of suitable material that is carried around by a person or placed with an object.

Thermoluminescence is a common [geochronology]] tool for dating pottery or other 'fired' archeological materials, as heat empties or resets the thermoluminescent signature of the material (Figure 1). Subsequent 'recharging' of this material from ambient radiation can then be empirically dated by the simple equation:

Age = (subsequently accumulated dose of ambient radiation)/(dose accumulated per year)


This technique was modified for use as a passive sand migration analysis tool by Keizars, et al., 2008 (Figure 2). This study shows direct consequences resulting from the improper replenishment of starving beaches using fine sands. Beach nourishment is a problem worldwide and receives large amounts of attention due to the millions of dollars spent yearly in order to keep beaches beautified for tourists (e.g. Waikiki, Hawaii). Sands with sizes 90-150 μm (very fine sand) were found to migrate from the swash zone 67% faster than sand grains of 150-212 μm (fine sand; Figure 3). Furthermore, the Keizars, et al., 2008 technique was shown to provide a passive method of policing sand replenishment and a passive method of observing riverine or other sand inputs along shorelines (Figure 4).



[edit] Literature

  • Thermoluminescence dating by M J Aitken, ISBN 0-12-046381-4
  • The Dating Game Scientific American June 11, 2001 page 2
  • Keizars, K.Z. 2003. NRTL as a method of analysis of sand transport along the coast of the St. Joseph Peninsula, Florida. GAC/MAC 2003. Presentation: Brock University, St. Catherines, Ontario, Canada.
  • Ķeizars, Z., Forrest, B., Rink, W.J. 2008. Natural Residual Thermoluminescence as a Method of Analysis of Sand Transport along the Coast of the St. Joseph Peninsula, Florida. Journal of Coastal Research, 24: 500-507.
  • Keizars, Z. 2008b. NRTL trends observed in the sands of St. Joseph Peninsula, Florida. Queen's University. Presentation: Queen's University, Kingston, Ontario, Canada.
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