RADIATION PROTECTION - ILEA

Historical Prologue
1 In the Beginning
Although our society has been concerned for some time with the potential
radioactive contamination of the environment resulting from the technological
exploitation of nuclear energy, the fact is that the universe is and always
has been permeated with radiation. At the present time there are
about one billion rays traveling through space for every elementary particle
of matter. The remarkable set of circumstances arising from the interaction
of radiation and matter has a history of some fifteen billion years. Some of
the most fascinating theories of physics attempt to explain how we arrived
at the present point in time and space, and how to account for the continuing
expansion of the universe and for its very low temperature (only 2.7
degrees above absolute zero!). The further backward in time we trace the
universe, the smaller and denser and hotter it was, until eventually we
come to the moment of birth—time zero—and the initial cosmic fluid.
How did it all begin? Some say the universe burst into existence with a
great big bang in which energy, space, time, and matter were created. The
progenitors of our entire observable universe, with the mass of a trillion
suns, were compressed into the volume of a single proton. In this tiny
space a myriad of extremely high energy particles collided with each other
at energies characterized by the astronomical temperature of 10 29 degrees
Kelvin (10 29 K). 1
1. These numbers are so high that we must express them as powers of 10, where the
power (the exponent) gives the number of zeroes following the one. For example, 10 4 =
10,000, 10 −4 = 1/10,000 = 0.0001. More will be said about units of energy and their significance
later, but for the moment note that the energies associated with radiations from
radionuclides are commonly under 2 million electron volts, an insignificant amount compared
with the energies released at creation.