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18.
Evaluation of Hazard from Internal Emitters
The use of the word "hazard" to denote radioactivity
in a biological sample,
regardless of kind or amount,
is
questionable and therefore is used here with reservation.
"Hazard" implies a risk or danger, which may or may not be
correct depending upon the point of view.
One point of
view is that all fonizing radiations are damaging and,
therefore,
a hazard exists even from one ionizing event.
The other point of view is that there can be some repair of
the damage caused by ionizing radiations,
thus,
if the
radiation dose does not result in an observable change,
hazard does not exist.
point of view,
In other words,
a
from this latter
there is a threshold level of radiation below
which there is no net effect.
A threshold level of ionizing radiation is more
generally accepted for effects upon somatic tissue rather
than upon genetic tissue.
There is reliable evidence which
demonstrates that the biological effect upon somatic tissues
of two equal doses of radiation administered over unequal
periods of time is less for the dose at the longer exposure.
These results have been interpreted to mean that some repair
has taken place and that ror very low levels of exposure,