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 Bomb-proof thermometer peeks inside big bangs

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Date posted: 01/10/2008

It is very difficult to accurately model explosions and predict the damage they will actually do. Mainly because we have never been able to study what actyually happens at the core of an explosion at the time of that explosion, in enough detail to precisely reconstruct it. The very nature of an explosion tends to destroy most sensors.

UK engineers at the UK's National Physical Laboratory have taken that as a challenge, and constructed a sensor - after many, many failed attempts, that does just that.

Gavin Sutton, leading the project, said, "An explosion generates a shock wave, significant amounts of heat, and particulate matter such as soot, all of which could degrade or damage a thermometer."

Conventional temperature sensors such as thermocouples, which measure the voltage produced when a metal is subject to a temperature gradient, are too slow to react and are easily damaged, says Sutton.

Bouncing laser light off objects can reveal temperature, too, but it is an expensive approach that is hard to use. So the team set out to find a new design to make a bomb-proof thermometer that could be used time and again.

The answer was an optical fibre 400 microns (0.4 mm) across, protected from the blast by a sand-packed steel tube with one open end. When the charge is detonated, thermal electromagnetic radiation enters the exposed end of the fibre and passes along it to a safe area beyond the reach of the explosion. There the fibre splits into four, with each branch piping its own specific set of wavelengths to devices that convert the radiation they receive into a voltage.

After performing calibration tests with bodies of known temperature, it is possible to transform those voltages into temperature readings, says Sutton. The thermometer can take 50,000 measurements per second, producing a detailed profile of temperature changes during a split-second detonation.

The result of all this experimentation will be directly used to increase the accuracy of computer predictions and models of explosions. Everything from blast damage, to appearance.

See the full Story via external site: technology.newscientist.com

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