ABSTRACT
INTRODUCTION12.1 Photons, that is, gamma-rays and X-rays, may be treated either as electromagnetic waves or as particles. An electromagnetic wave is characterized by its wavelength λ or frequency ν. A photon is a particle having zero charge and zero rest mass, traveling with the speed of light, and having an energy E = hν, where h = Planck’s constant. The wave properties of a photon are used for lowenergy measurements only. In all other cases, detection of photons is based on their interactions as particles.
