A $23\mathrm{.}5$ pm x$-$ray photon scatters off a free electron at $A($see the figure below$),$ producing a photon of wavelength ${}^{\text{'}}$ traveling at an angle $=41\mathrm{.}0$ relative to the first photo direction. This second photon scatters off another free electron at $B,$ producing a photon with wavelength ${}^{\text{'}\text{'}}$ and moving in a direction directly opposite the first photon. Dete wavelengths ${}^{\text{'}}$ and ${}^{\text{'}\text{'}},$ both in pm$.$

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