Anomalous energy loss and straggling of 24.8-MeV electrons through thin single crystals of Si and Ge

Anomalous broadenings in straggling distributions of 24.8-MeV electrons are found along Si 〈100〉 and Ge 〈110〉 axial directions, and incident-angle dependence of these anomalies is studied around each axis. Additional broadening ΔΓ to the full width at half-height Γ of the straggling distribution reaches 7.7 keV (ΔΓΓ=8.5%) along the axis of 0.2067-g/cm² Si and 11.0 keV (ΔΓΓ=11.0%) along the axis of 0.2155-g/cm² Ge. These can be interpreted as a consequence of radiation loss associated with a large enhancement of coherent low-energy-photon emission.