= Solution
A heated <cathode> emits <electrons>, accelerated through a potential difference onto a metal target. Deceleration produces a <bremsstrahlung> continuum with $\lambda_{\min}=hc/(eV_{\rm acc})$; inner-shell ionization followed by electronic relaxation produces characteristic lines. The pictured instrument is consistent with the copper-target TEL-X-Ometer used for teaching diffraction. Its <copper> $K_\alpha$ radiation has wavelength about $0.154\,\mathrm{nm}$, comparable with atomic plane spacings. A <nickel> filter preferentially suppresses <copper> $K_\beta$, while slits collimate the beam; filtering does not remove every continuum <photon>.
A <Geiger-Müller counter> converts photon-induced gas ionization into countable electrical pulses. A scintillator with <photomultiplier> is another detector option. A detector-arm scan records count rate against scattering angle; coupled crystal rotation preserves the usual reflection geometry. These instrument features are documented by its manufacturer.<TEL-X-Ometer X-Ray System Manual by Joseph Dohm>[Sections 3.5–3.6 and 7.1: crystal/detector geometry and detection; section 4.6: copper characteristic wavelengths]{ref}
For the numerical calculations below use \b[$\lambda=0.154\,\mathrm{nm}$], explicitly identifying the characteristic line assumed. The photograph alone does not give a measured wavelength or angular travel limit; conclusions depending on these parameters are stated conditionally. A different selected line changes the angles but not a crystallographic extinction.
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