Compton Scattering Calculator

How it is calculated

The shift depends only on the scattering angle, not on the photon's starting energy: Δλ = λc · (1 − cos θ). Here θ is the angle in degrees between the incoming and outgoing photon directions, and λc = h / (mₑc) is the electron's Compton wavelength, which the tool takes as 2.42631023867×10⁻¹² m. The angle is converted to radians internally, and the result is given in picometres (pm) and in metres in scientific notation.

The model assumes the electron is free and at rest before the collision. The result is the increase in wavelength, not the final wavelength of the photon.

Common mistakes

• Entering the angle in radians. The field expects degrees, so π/2 typed as 1.57 gives a tiny angle, not 90°.
• Reading the result as the new wavelength. It is only the change Δλ; add it to the original wavelength yourself.
• Confusing the scattering angle with the angle of the electron's recoil. The formula uses the photon's deflection from its original direction.
• Mixing picometres and metres: 1 pm is 10⁻¹² m, so 1.2132 pm equals 1.2132e-12 m.
• Expecting the shift to depend on the photon's energy. It does not, though the relative shift is only noticeable for short wavelengths such as X-rays.