= Compton scattering experiment of 1923
{c}
In <Arthur Holly Compton>'s https://doi.org/10.1103/PhysRev.21.483[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 $90^\circ$ <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>.<A Quantum Theory of the Scattering of X-rays by Light Elements by Arthur Holly Compton>[Compton, Physical Review 21 (1923), pp. 494–496, Experimental Test, Figure 4 and opening of Velocity of recoil of the scattering electrons]{ref}
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