Civil Engineering Reference
In-Depth Information
radioactive cloud:
noble gases, iodine, aerosols
radioactive cloud:
noble gases, iodine, aerosols
contamination
of skin and
clothes
contamination
of skin and
clothes
inhalation
inhalation
external
external
- irradiation
ingestion
ingestion
contamination of ground and of food and feed stuffs
contamination of ground and of food and feed stuffs
Fig. 20.2
Radiation exposure of humans, animals, and vegetation, by terrestrial exposure
pathways
disintegrations as the radioactive cloud passes through a specific volume element
for a given time period is referred to as the time-integrated nuclide concentration,
Bq s/m
3
.
The time-integrated concentration in air close to the ground determines the
contamination of surfaces by dry deposition and the inhalation of radioactive
material from the cloud by humans and animals; cf. Figs.
20.1
and
20.2
. However,
it is in particular the wet deposition resulting from the cloud being washed out by
precipitation that can considerably increase the contamination of surfaces and thus
lead to a much higher longer-term external
-radiation exposure from the ground
and contamination of food and feed stuffs; cf. Figs.
20.1
and
20.2
. Deposition
processes are specific to nuclide groups: noble gases are not deposited at all while
aerosols and iodine gas (elemental or bound organically) are subject both to dry and
wet deposition.
External
γ
-radiation from the cloud and from contaminated surfaces is partly
absorbed by the human body, and results in organ doses.
Skin contamination of humans arises from radionuclide deposition onto the
uncovered (bare) skin. Especially wet deposition of beta emitters on the skin can
cause significant doses to the skin itself. Contamination of both skin and clothes
causes
γ
-particles, however, have such a
short depth of penetration that they will not reach the radiation-sensitive layer of the
skin, thus not giving rise to a relevant skin or organ dose.
Inhalation of iodine and aerosols from the air leads to an uptake of radionuclides
into the body and subsequently to organ doses by internal
γ
-exposure of the skin and the whole body.
α
α
-,
β
-, and
γ
-radiation. A
well-known example is the internal
β
-exposure of the thyroid by inhaled radioactive
