Thermoluminescence

Sponsor
Defense Threat Reduction Agency
Collaborators
Oklahoma State University
NSWC Indian Head Division
Vinča Institute of Nuclear Sciences

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Thermoluminescent Temperature Sensing of High-Explosive Detonations

Or, How I Learned To Stop Worrying And Love The Bomb

The inside of a high explosive detonation fireball is a place so violent, no contact sensor can brave the conditions within. If you want to know how hot it is, you have to measure it optically from a safe distance and hope you’re not blocked by debris, smoke, and other parts of the fireball.

We aim to change that.

Mechanism

Thermoluminescence (TL) is a phenomena found in certain materials which can trap charge carriers produced by ionizing radiation and store them until they are released by heat, whereupon they recombine and emit light. The TL project repurposes these materials–some new, some well-known for radiation dosimetry purposes–as incredibly tough, tiny, solid-state temperature sensors, irradiating TL particles before detonating them in explosives and reading out their remaining luminescence to reconstruct their ride.

Irradiated TLD-200 chips being heated on a hotplate, displaying two distinct emissions peaks: one green… …and one blue.
These particles are working micro-scale temperature sensors. …and so, post-detonation and mixed with blast debris, are these.

MEMS

Of course, we wouldn’t be the Optical MEMS Group if we just stopped at microparticles. Tiny microscale electric heaters can heat and cool at speeds that are impossible for large hotplates, allowing us to subject the particles to explosion-like temperatures (okay, the mild ones) without actually blowing them up. (The administration gets very unhappy about too many explosions in the labs.)

Microheaters with magnesium silicate microparticles.
Microheaters with magnesium silicate microparticles.

Of course, explosions also involve violent accelerations and a good deal of strain on whatever is flying around in the vicinity. Large-area membranes–sheets of material hundreds of nanometers thick, yet centimeters on a side–allow us to stress a thermoluminescent film by electrically flexing its substrate.

A bare silicon nitride membrane, with a penny for scale.
A bare silicon nitride membrane, with a penny for scale.
An electrostatically-actuated membrane being wired up for testing.
An electrostatically-actuated membrane being wired up for testing.

TL Thin Films

Thin films capable of thermoluminescence were grown using electron-beam evaporation and characterized by identifying the crystalline structure and measuring the emission spectra.

A measurement of the spectral response of a Y2O3:Tb thin film at varying temperatures.
A measurement of the spectral response of a Y2O3:Tb thin film at varying temperatures.

(To be continued)

Other Research

Laser Damage

Optical Materials and Laser Damage

Infrared

Spectrally-Selective Uncooled Infrared Bolometers

Ice

Optical Characterization of Glacial Ice

Thermoluminescence

Thermoluminescent Extreme-Environment Temperature Sensors

Quantum Tuning

Tuning the Semiconductor Bandgap: Nanomechanical Control of Electron States

About (TL;DR)

We are the ECE research group of Professor Joey Talghader at the University of Minnesota.

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