= Bragg crystal reflection experiment of 1913
{c}
<William Lawrence Bragg> introduced the plane interpretation; his father <William Henry Bragg> built the <X-ray> spectrometer. Their joint 1913 paper, https://doi.org/10.1098/rspa.1913.0040[The Reflection of X-rays by Crystals], reports the experiment. <The Bragg law (University of Leeds Library Special Collections)>[The Bragg law: Lawrence's 1912 interpretation and the angle convention]{ref} <William Bragg's spectrometer (Royal Institution collection)>[Description: William Henry Bragg designed and made the spectrometer]{ref}
An <X-ray tube> supplied radiation through lead slits to a crystal mounted with its cleavage face through the rotation axis. A rotating <ionization chamber> replaced a spectrometer telescope; <electric current> measured the scattered signal, and a circular scale supplied angular readings. They first scanned the chamber at fixed crystal orientation, then swept crystal and chamber together to follow the reflection. <The Reflection of X-rays by Crystals by William Henry Bragg and William Lawrence Bragg>[Bragg and Bragg (1913), pp. 428–430: preparation, source, slits, chamber, angular scale and scanning]{ref}
Changing chamber gas checked detector dependence; readings on opposite sides checked face-setting errors. Repeated peaks with <sines> of half-deflections in integer ratios, together with matching <absorption coefficients>, distinguished repeated <diffraction orders> of the same <wavelength> from different radiation components. Comparing crystal faces constrained <interplanar spacings>. Their limits included slit broadening, face alignment and incomplete interception at glancing incidence; assigning absolute <wavelengths> still required a structural choice for $d$. <The Reflection of X-rays by Crystals by William Henry Bragg and William Lawrence Bragg>[pp. 428–430: gas and alignment controls; pp. 435–437 and Fig. 3: order comparison, absorption test, finite-face limitation and spacing ambiguity]{ref}
Back to article page
