SCI-FI-TEK

We've Never Seen Cherenkov Radiation During a Fusion Reaction... Until Now

Darren Orf
Wed, October 18, 2023 

Fusion Sends Particles Faster than Lightspeed

Argonne National Laboratory

When a particle exceeds to the speed of light in a medium, such as water, it produces whats known as Cherenkov radiation.


This radiation is used by nuclear inspectors and astronomers, but it’s never been observed during a fusion reaction—until now.


The U.S.-based fusion company SHINE announced earlier this month that they witnessed the phenomenon during a deuterium-tritium fusion process.

When an object travels faster than the speed of sound, it produces a sonic boom. Something similar also occurs when particles travel faster than the speed of light. While light’s velocity in a vacuum sets the speed limit for the universe, when traveling through water, that limit decreases to about 75% its usual speed—about 139,800 miles per second. If a particle exceeds that limit, it produces an eerie blue glow called Cherenkov radiation. The effect is named after Soviet physicist Pavel Cherenkov, who won a Nobel Prize for his discovery.

This blue glow is a well-known phenomenon in fission circles, as nuclear reactors are regularly submerged in water. In fact, nuclear inspectors use this light to discern whether nuclear material is being used for peaceful means. Astronomers are also aware of this phenomenon, and the IceCube Neutrino Observatory leverages this effect to detect muon neutrinos in Antarctic ice.

However, the effect has never been seen during a fusion reaction—until now. Last month, the nuclear fusion company SHINE announced that Cherenkov radiation was visible during its deuterium-tritium fusion process. This was the first time that the blue-hued phenomenon was captured during a fusion reaction.

“The Cherenkov radiation effect produced here was bright enough to be visible, which means there’s a lot of fusion happening, about 50 trillion fusions per second,” Gerald Kulcinski, director of Fusion Technology-Emeritus at the University of Wisconsin-Madison, said in a press statement. “At a billion fusions per second, you might have measurable Cherenkov radiation but not visible amounts.”

Deuterium and tritium are two isotopes of hydrogen, also known as heavy hydrogen. Unlike normal hydrogen,which usually only has one proton (giving it the number one spot on the periodic table), deuterium contains a neutron and proton, and tritium contains two neutrons and a proton. SHINE uses a deuteron beam—essentially just the nucleus of deuterium—to hit tritium at high speeds, according to IFLScience.

So, why do particles emit this blue glow during a fusion reaction in the first place? When hydrogen absorbs a neutron, it emits a high energy gamma ray. When this gamma ray knocks into an electron, the ray can accelerate the electron beyond the speed of light (in water). When the particle exceeds that threshold, it produces a “shock wave,” much like sound waves. Because of the high energies at play, the light travels at high frequencies and short wavelengths, which correspond with the cooler end of the visual spectrum.

SHINE’s fusion reactors are mostly used to study the effects of radiation, whether in aerospace or medical applications, though it expresses interest in developing fusion for energy-producing purposes. Witnessing Cherenkov radiation during the fusion process brings with it some hope that fusion technology can one day produce neutrons on par with more traditional fission reactors.