Coherent Visible Radiation of Fast Electrons Passing Through Matter

Abstract

In 1934 P. A. Čerenkov has discovered a peculiar phenomenon, whicd he has since investigated in detail (¹). All liquids and solids if bombarded by fast electrons, such as β-electrons or Compton electrons produced by γ-rays, do emit a peculiar visible radiation, quite different from the eventual ordinary flourescence. This radiation is partially polarized, the electric oscillation vector being parallel to the electron beam, and its intensity can be reduced neither by temperature nor by addition to the liquid bombarded of quenching substances. The peculiarity of these carac-teristics was scrutinized by Wawilow (²) who suggested that this radiation must be connected with the «Bremsung» of fast electrons. Since then a new and undoubtedly the most peculiar characteristic of the phenomenon was discovered, namely, its highly pronounced asymmetry, the intensity of light emitted, in the direction of the motion of electrons being many times larger than in the backward direction. It follows that the substance bombarded radiates coherently for the space of at least one wavelength of the visible light.