Civil Engineering Reference
In-Depth Information
dynamic food chain transport model. For obtaining realistic results for a given
locale, dynamic models need a region-specific data base containing information
about soil types, vegetation periods, agricultural production habits and production
rates, and food consumption rates.
20.5 Calculation of Doses for the Terrestrial Exposure
Pathways
For deriving pathway-specific doses on the basis of the concentration and contam-
ination fields determined with the atmospheric dispersion models, further steps are
necessary for covering the different terrestrial exposure pathways:
• Calculation of the cloud gamma irradiation field and of the resulting dose
• Calculation of the gamma irradiation from the radionuclides deposited by dry
and wet deposition processes on urban and agricultural areas (summarily
referred to as ground irradiation) and of the resulting dose
• Determining the internal exposure from inhalation of contaminated air from the
cloud and of activity resuspended from the ground, and the resulting dose
• Determining the internal exposure from ingestion of contaminated food, and the
resulting dose
The different exposure pathways require different model approaches which are
described below, separately for “Doses from the Cloud and from Contaminated
Surfaces” and “Doses from the Food Chains”.
20.5.1 Doses from the Cloud and from Contaminated
Surfaces
Figure
20.7
illustrates the different steps for calculating gamma dose rates and
doses from the cloud and from the contaminated ground.
An analytical calculation of the gamma-radiation field from the cloud requires
sophisticated mathematical solutions of complicated integral equations and is
therefore often replaced by approximations or interpolations between data tables.
Calculating gamma-irradiation from the ground is easier; most models assume
“(ideal) lawn” as a reference surface and the geometry of a plane and infinite
contaminated surface. Any contaminated structures (trees, buildings) deviating
from the plane surface are taken into account by local factors.
The transit from radiation fields to absorbed doses (unit: Gray
¼
Gy
¼
Joule/kg)
and to biological equivalent doses (unit: Sievert
Sv) requires the modeling of the
physical absorption processes and the biological effects in the organs of the human
body for the nuclides involved. The results of such model calculations are then
¼
