Observation of soft X-ray Cherenkov radiation in Al

The soft X-ray radiation generated by 5.7 MeV electrons from both an Al foil and a Mylar film in forward direction was experimentally studied. A narrow specific directivity, an ultra-narrow spectral bandwidth and a good consistency between the experiment and theory prove that the Cherenkov radiation (CR) with photon energy near the L-edge of absorption in Al was observed. The results demonstrate that the CR spectral-angular properties and the absolute photon yield can be described well enough using Pafomov's theoretical model and Henke's refractive index database, which is essential for all practical applications