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 $\Delta \Gamma$ to the full width at half-height $\Gamma$ of the straggling distribution reaches 7.7 keV ($\frac{\Delta \Gamma }{\Gamma }=8.5\%$) along the axis of 0.2067-g/${\mathrm{cm}}^2$ Si and 11.0 keV ($\frac{\Delta \Gamma }{\Gamma }=11.0\%$) along the axis of 0.2155-g/${\mathrm{cm}}^2$ Ge. These can be interpreted as a consequence of radiation loss associated with a large enhancement of coherent low-energy-photon emission.