Sonoluminescence is the emission of light by tiny bubbles created when ultrasonic waves excite a liquid, with noble gases magnifying the effect. The phenomenon was discovered in 1934 and has been studied since 1989. While temperatures in excess of 20,000 K have been measured, sonoluminescence is not hot enough to initiate nuclear fusion reactions. The effect has no practical application, but there are shrimp that show sonoluminescence when they snap their claws.
Sonoluminescence is a mysterious phenomenon that occurs when ultrasonic waves excite a liquid, creating tiny bubbles that emit light as they collapse. The effect is magnified when the bubbles contain a noble gas. The phrase sonoluminescence means “sound light”.
There are various theories of sonoluminescence, none of which have been conclusively proven. Temperatures in excess of 20,000 K have been measured at the center of these tiny bubbles. This is hot enough to boil the diamond.
The phenomenon of sonoluminescence was popularized in the Keanu Reeves film Chain Reaction. In the film, sonoluminescence is used to start a nuclear fusion reaction. Bubbles created by sonoluminescence have been observed generating temperatures measuring in kilokelvins, or tens of thousands of degrees. The temperature threshold for initiating nuclear fusion reactions is millions of degrees, or megakelvins. There is a bit of a discrepancy here, a discrepancy that adds up to three orders of magnitude. Sonoluminescence is hot, but not that hot.
Researchers in Purdue scientist RP Taleyarkhan’s lab said that, under sonoluminescence, a vessel filled with acetone emitted neutrons at a statistically significant level, the signature signature of fusion. However, these results have never been duplicated and were summarily rejected in a Nature paper in 2006. Taleyarkhan’s patent for the device was rejected and an analysis was published by B. Naranjo showing his data is been misinterpreted.
The sonoluminescence effect was first discovered by German scientists H. Frenzel and H. Schultes at the University of Cologne in 1934. They were attempting to speed up the process of developing photos, but ended up observing luminous bubbles instead. Because the effect was so random and uncontrollable, it wasn’t scientifically studied until much later.
In 1989, Felipe Gaitan and Lawrence Crum were able to create a bubble of sonoluminescence that remained in a constant place: an ultrasonic standing wave periodically generated a bubble and then let it collapse. This was a big step forward and allowed the phenomenon to be analyzed in a laboratory setting. The bubbles were found to be extremely small when the light was released, about a micrometer wide or about the size of a bacterium. The duration of the flashes is extremely short, even if overall they can be observed with the naked eye: each flash lasts from a few tens to a few hundred picoseconds, the time it takes for light to move a few centimetres.
While sonoluminescence is a surprising effect, it currently has no practical application and will probably never be exploited for fusion energy. Surprisingly, there are shrimp that snap their claws so fast that they show sonoluminescence. Scientists with a sense of humor have called this shrimp effect luminescence.
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