Compton Scattering (Photon Billiards)
Fire an X-ray or gamma photon at an electron and watch it bounce off with less energy — the wavelength shift depends only on the angle, which is the evidence that light comes in particles.
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What you can adjust
- Incident photon energy
- 8.05 – 1250 keV
- Scattering angle (theta)
- 0 – 180 °
- Animation duration
- 1 – 4 s
The X-ray or gamma photon's energy before it hits the electron. A higher-energy photon hands a bigger fraction of its energy to the electron for the same scattering angle.
The angle the photon comes off at, measured from its original direction. 0 degrees means it barely deflects at all (no energy loss); 180 degrees is a dead-on backscatter (the biggest possible energy loss).
How long the clip runs — the photon travels in, then the scattered photon and recoil electron fly apart.
About this simulation
What it shows
An X-ray or gamma-ray photon hits an electron and bounces off with less energy, while the electron recoils. The photon's new wavelength and energy are read out.
The key idea
The photon behaves like a particle that shares its energy and momentum with the electron. The wavelength grows by (h/mc)(1 − cos θ), which depends only on the scattering angle and not on the photon's energy.
Try this
Raise Scattering angle (theta) from 90° to 180°: the shift in wavelength doubles, from about 2.43 pm to 4.85 pm, whatever the photon energy.