Radiation processes
The emission of electromagnetic radiation tends to be formulated in
terms of one or more of the classical named radiation processes, most
commonly blackbody, synchrotron, transition, and Cherenkov radiation,
bremsstrahlung etc. However, these terms are simply short-hand for the
radiation observed in a precise set of physical circumstances,
e.g. ultra-relativistic particles spiralling infinitely in magnetic
fields in the case of synchrotron radiation, or a particle travelling
an infinite distance in a uniform dielectric in the case of Cherenkov
radiation. They are not fundamentally distinct physical processes. In
a complex physical situation - such as a cascade of particles from a
cosmic-ray interaction in the Earth's atmosphere, or even something as
simple as a particle spiralling in a magnetic field in a dielectric -
the distinction between these radiation processes becomes both blurred
and arbitrary. In such circumstances, it is best not to artificially
distinguish between processes and simply stick to the well-known (and
mostly correct) maxim ``accelerated charged particles produce
electromagnetic radiation''.
To handle complex radiating systems in a logical fashion, researchers
in Nijmegen are developing the `end-point' methodology, by which
radiation is calculated from an instantaneous particle
acceleration/deceleration event. In this way, the dependence of the
radiation on the acceleration is made explicit, avoiding the “is it
Cherenkov? Is it transition?” questions which have plagued previous
calculations. Complex physical situations can be described via a
super-position of these 'end-points'. This methodology is being used
to calculate the radiation from cosmic-ray and neutrino interactions
in the Earth's atmosphere and the Moon, and has already been used to
show that the radiation from the Askaryan Effect in a dense medium is
not (as previously thought) coherent Cherenkov radiation, but in fact
coherent bremsstrahlung.
Links & Selected Papers
Members
