Friday is here, and with it the weekly "A Taste of Physics" column — number 44.
This week: Cherenkov radiation, and its fascinating connection to nuclear reactors and fighter jets.
-
The video shows an energy pulse in the core of a nuclear reactor.
The reactor core contains rods of fissile material (uranium-235, for example), along with other rods used to slow down the chain reaction during the fission process when needed.
The water serves to absorb the enormous heat generated by nuclear fission and carry it out of the core, where it can be used as an energy source.
But why does the core suddenly glow blue?
-
Nothing can travel faster than light.
This is one of the most absolute principles in modern physics, rooted in Einstein's theory of relativity.
However, particles *can* move faster than light if the light slows to a speed lower than that of the particle — and the radiation emitted under these conditions is known as Cherenkov radiation.
When subatomic particles travel through a medium — water, in this case — the photons they emit repeatedly encounter atoms in their path, are absorbed by them, and re-emitted.
This passage through atoms slows the light waves, while the particle itself continues moving at high speed.
Because the particle is moving faster than the light waves it emits, those waves accumulate into high-frequency — blue — radiation that trails behind it in the shape of a cone.
In truth, most of the radiation emitted in this way is entirely invisible to us due to its high frequency; what we actually see are the lower-frequency components that fall within the visible light spectrum.
-
The same phenomenon can be observed in the wake of a ship.
The ship's rapid motion causes waves to pile up and trail behind its stern in a cone of high crests.
Sonic booms produced by fighter jets arise from exactly the same principle.
The aircraft moves faster than the sound waves it generates, causing them to accumulate into high frequencies heard as an explosion.
-
The discoverer of this radiation was awarded the Nobel Prize for it.
Cherenkov radiation is used to monitor the activity of nuclear reactors (during scientific experiments), to monitor cancer radiotherapy treatment, and even to detect cosmic rays that strike the atmosphere and emit this very radiation.
Shabbat Shalom 😊
#ATasteOfPhysics