RADIATION PROTECTION - ILEA

PART
ONE
Energy—The Unifying Concept in
Radiation Protection
1 Radiation’s Dual Identity
Dictionaries often describe radiation as waves or particles that propagate
through space. The fact is that any radiation emission can be observed either
as a subatomic particle or as a wave, depending on how it is detected.
This is a remarkable phenomenon, since the concepts of waves and particles
are diametrically opposed. A particle is a discrete object that transmits
energy by moving from one point to another. Appropriate measurements
give its mass and velocity, or its momentum (which is the product of mass
and velocity). A wave is also a means of transmitting energy between
two points, but the journey is not made by a discrete identifiable object.
Rather, the energy is conveyed through oscillations in time of a physical
property at each point along the path. For example, an ocean wave smashing
against the coast may have originated hundreds of miles offshore from
wind action, but no intact mass of water travels this distance and wind is
not needed to propagate the wave. A local circular oscillation of the surface
of the water is initiated at some point, and this motion is transmitted in
succession to adjacent elements of water until it reaches the shore. Leonardo
da Vinci wrote of water waves, “It often happens that the wave flees
the place of its creation, which the water does not; like the waves made in a
field of grain by the wind, where we see the waves running across the field,
while the grain remains in place” (cited in Halliday and Resnick, 1988,
p. 392).
If radiation is detected as a wave, measurements give its wavelength and
frequency or, in some cases, a group of frequencies. Radiation emitted
from antennas is normally treated as waves. High-energy radiation, such as
is emitted in the process of radioactive decay or produced by x-ray ma-