Abstract
While there are innumerable devices that measure temperature, the nonvolatile measurement of thermal history is far more difficult, particularly for sensors embedded in extreme environments such as fires and explosions. In this review, an extensive analysis is given of one such technology: thermoluminescent microparticles. These are transparent dielectrics with a large distribution of trap states that can store charge carriers over very long periods of time. In their simplest form, the population of these traps is dictated by an Arrhenius expression, which is highly dependent on temperature. A particle with filled traps that is exposed to high temperatures over a short period of time will preferentially lose carriers in shallow traps. This depopulation leaves a signature on the particle luminescence, which can be used to determine the temperature and time of the thermal event. Particles are prepared—many months in advance of a test, if desired—by exposure to deep ultraviolet, X-ray, beta, or gamma radiation, which fills the traps with charge carriers. Luminescence can be extracted from one or more particles regardless of whether or not they are embedded in debris or other inert materials. Testing and analysis of the method is demonstrated using laboratory experiments with microheaters and high energy explosives in the field. It is shown that the thermoluminescent materials LiF:Mg,Ti, MgB4O7:Dy,Li, and CaSO4:Ce,Tb, among others, provide accurate measurements of temperature in the 200 to 500 °C range in a variety of high-explosive environments.
Highlights
Temperature measurement devices abound: a simple web search for commercial products using the keywords ‘temperature sensor’ gives almost 1000 different possibilities, and these primarily only encompass general consumer-oriented applications
TL and optically stimulated luminescence (OSL) materials have applications in dosimetry[29,30] and archeological dating[31,32], where empty trap defects are slowly filled with charge carriers by radiation; the dose or time of exposure can be determined by observing the number of photons produced during a luminescence measurement
The particles are hard durable oxides and fluorides that can withstand very harsh environments without contaminating their surroundings or decomposing. They operate based on an Arrhenius expression, which emphasizes the highest temperatures that are most important in determining a thermal dose
Summary
Temperature measurement devices abound: a simple web search for commercial products using the keywords ‘temperature sensor’ gives almost 1000 different possibilities, and these primarily only encompass general consumer-oriented applications. TL and OSL materials have applications in dosimetry[29,30] and archeological dating[31,32], where empty trap defects are slowly filled with charge carriers by radiation; the dose or time of exposure can be determined by observing the number of photons produced during a luminescence measurement.
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