Civil Engineering Reference
In-Depth Information
The energy of ionizing radiation impacting on living creatures can be absorbed
partly or completely inside the cells. It is primarily the absorption by ionization
processes in the cell's molecules, especially in the deoxyribonucleic acid (DNA)
that causes biological radiation effects. Many DNA defects are fully repaired by
endogenous repair mechanisms. If the repair turns out to be faulty, however, there
may be permanent changes in the DNA (mutations) which can lead to health
detriments after a latency period of years or even decades. If cell regeneration is
impossible at all or takes too long because the damage is too severe or too extended,
there may be cell death either right after exposure or somewhat later.
DNA mutations in cells of the body can cause somatic (physical) effects, such as
leukemia, tumors or cancer; they affect the individual exposed. Mutations in germ
cells cause genetic (hereditary) effects; they affect potential progeny of an exposed
individual. With respect to all radiation-induced detriment caused by DNA muta-
tions it is assumed that there is no threshold dose
3
for the manifestation and that the
severity does not depend on the dose—an increase in radiation dose will add to the
probability of occurrence but not change the type of effect. This type is thus referred
to as a “stochastic radiation effect”. The risk of damage is expressed as the
probability of occurrence per unit dose, with the risk numbers taken from epide-
miological studies of larger populations exposed to radiation and dependent on a
multitude of parameters, such as gender and age of the individuals.
Acute radiation detriments occur either immediately or within days or weeks
4
after the exposure to high radiation doses; the manifestation can be temporary or
permanent. Unlike stochastic radiation effects, such damage can be related to the
radiation exposure of the affected individual, and is therefore referred to as a
“deterministic radiation effect”. As a rule, these effects are the consequences of a
massive killing of cells in an organ or tissue; if this exceeds a certain level, the
affected organ or tissue will lose its functionality. Once a threshold dose has been
exceeded, the severity of the injury increases with the dose, and the injury occurs
relevant loss of function as a result of radiation exposure is expected below an
absorbed dose of approx. 100 mGy.
5
A survey of deterministic effects and their
threshold levels can be found, e.g., in ICRP-103 in Annex A.
3
Very low threshold levels are under discussion, too. Not finally clarified, this discussion plays no
fundamental role in emergency management.
4
Radiation-induced cataracts manifest only after some years.
5
The absorbed dose [Gy] is to be used for assessing deterministic effects, and the dose equivalent
[Sv] for determining stochastic effects. For loosely ionizing radiation, the numerical values are
the same.
