NUCLEAR & PARTICLE PHYSICS · INTERACTIVE LAB 76
Cherenkov Radiation Laboratory
Explore the luminous shock cone produced when a charged particle outruns light’s phase velocity in a transparent medium.Charged particleWavefrontCherenkov coneThreshold
Particle speed0.990c
Medium light speed0.750c
Threshold β0.750
Cherenkov angle40.8°
Threshold margin0.320
Relative intensityIllustrative
Wavefront coherence
Speed comparison
particle β
c/n
vacuum c
0c/n < v < c — Cherenkov radiation is allowed without violating relativity.1.0c
Physics
v > c/ncos θ = 1/(nβ)βthreshold = 1/n
An optical shock wave
A charged particle polarises molecules along its path. If it travels faster than light’s phase velocity in that medium, the emitted wavefronts overlap coherently and form a cone—similar to a sonic boom.
No broken speed limit
The particle remains slower than light in vacuum. Transparent matter reduces light’s phase velocity to c/n, making c/n < v < c possible.
Why the glow is blue
The idealised emission spectrum favours shorter wavelengths. Real colour also depends on dispersion, absorption, detector sensitivity and the observer’s response.