7
It is important to note that the field intensity from a radioac-
tive object decreases very quickly with distance.
If the object is very small, increasing the distance from the
object by a factor of two decreases the radiation level by a
factor of four. This is called a square law situation, which
demonstrates the dependence of proximity on dose for
small radioactive sources. Larger sources, such as a large
deposit of radioactive minerals, will show much less of this
effect. In trying to estimate the danger of radioactive mate-
rials, it is important to take into account many aspects of
the situation. For instance, the radiation level at the face of
a radium-dial watch may be 3mR/hr, but the measurement
taken from the back of the watch may be 0.3mR/hr.
Another interesting point concerns the energy of the radia-
tion. Geiger Counters will register one click whenever they
detect a ray or particle of radiation hitting them. These tiny
high speed bundles of energy are like short bursts of light.
Some are extremely energetic, while others are not. Geiger
Counters cannot determine the energy of the impinging ray,
they only detect its presence. Sper Scientific models
840007 and 840026, detect Beta and gamma radiation
starting at approximately 30KeV and up to 1.5 MeV.
The opposite is the case for cosmic rays, which have enor-
mous energy — some millions of times more energetic than
anything found here on earth. The compensation figure for
radiation of this type is difficult to estimate, due to the ex-
treme range of energies that have been measured.
RADIATION — WHAT IS IT?
Nuclear physics is a very complex field, however, the basic
principles can be simply explained.
All matter is composed of atoms. Atoms alone and bonded
together in molecules form all the things around us, includ-
ing ourselves. These atomic units are extremely small; so
small, in fact, that a single grain of table salt contains ap-
proximately 1,000,000,000,000,000,000 atoms (this is not a
misprint). It is impossible to see an atom, except with a so-
phisticated electron microscope, so many of our present
day theories on the structure and composition of single at-
oms are based largely on the study of radiation given off
from unstable (radioactive) substances.
