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 Incoming links: Arthur Holly Compton

By Arthur Holly Compton, printed as Arthur H. Compton. Published in Physical Review 21, 483–502, May 1923. The Norwegian University of Science and Technology hosts this copy of the original paper.

Arthur Holly Compton Created 2026-10-18 Updated 2026-11-05

Arthur Holly Compton explained the angle-dependent change of X-ray wavelength by treating a photon as carrying both energy and momentum. For scattering from an initially stationary free electron, conservation gives

λ^{'} - λ = h (1 - cos θ) / (m_{e} c)

. The Compton scattering shift therefore depends on angle and the electron mass, rather than on the illuminating wavelength alone. Comparing the measured scattered lines with this relation tested the particle-like energy–momentum account of radiation.^[ref]

Compton scattering experiment of 1923 Created 2026-10-18 Updated 2026-10-20

In Arthur Holly Compton's A Quantum Theory of the Scattering of X-rays by Light Elements (1923), pp. 494–495 and Figure 4 compare X-rays from a molybdenum target with rays scattered by graphite at right angles. Slits select the rays; a calcite crystal analyzes their wavelengths by Bragg's law. The plotted readout is scattered wave intensity against the crystal's glancing angle, distinct from the fixed

9 0^{\circ}

photon deflection. The primary-beam comparison uses the same slits, crystal, and tube potential. First-order diffraction lines on both sides establish angular zero. The displaced spectral line supports a longer outgoing wavelength and hence photon energy transfer. The two curves use different vertical scales, so their heights cannot directly compare absolute wave intensities. The paper postpones a fuller apparatus description; it also states on p. 496 that recoil electrons from ordinary X-rays had not been observed. Thus this spectral test infers recoil through the conservation model rather than directly tracking an electron.^[ref]

In Compton scattering, a photon transfers energy and momentum to an initially stationary, approximately free electron. With incident and scattered wavelengths

λ, λ^{'}

and photon deflection angle

θ

, momentum conservation gives

p_{e}^{2} = h^{2} (λ^{- 2} + λ^{' - 2} - \frac{2 c o s θ}{λ λ ^{'}}) .

Combine this with

h c / λ + m c^{2} = h c / λ^{'} + m^{2} c^{4} + p_{e}^{2} c^{2}

to obtain

λ^{'} - λ = \frac{h}{m c} (1 - cos θ) .

The photon loses energy to electron recoil; the shift is independent of incident wavelength in this free-electron model and is largest at backscattering. At energies comparable with atomic binding, initial electron motion, binding and coherent scattering from the atom require additional treatment. Classical elastic scattering from a fixed charge alone does not produce this recoil wavelength shift.

9 0^{\circ}

were compared with the primary spectrum using the same slits, crystal and tube potential energy. A calcite crystal resolved the shifted line by Bragg's law; lines on both sides established angular zero. The crystal glancing angle on the plotted axis differs from the photon scattering angle. The compared curves had different intensity scales, and the paper did not directly observe the recoil electrons in this X-ray test. These controls support the wavelength comparison without converting it into a direct recoil-track measurement.^[ref]