Civil Engineering Reference
In-Depth Information
Cloud gamma radiation
field
Cloud gamma radiation
field
Gamma radiation field
from contaminated surfaces
Gamma radiation field
from contaminated surfaces
Air contamination near
ground
Air contamination near
ground
External irradiation
External irradiation
Inhalation rates
Inhalation rates
Dose rate factors
Dose rate and dose factors
Internal irradiation
Internal irradiation
Dose rates
cloud
Dose rates
ground
Dose rates
ground
Dosisraten
Boden
Dosisraten
Boden
Dose factors
Local
Local
Ortsdosisleistung
Ortsdosisleistung
g
g
dose rates
dose rates
Gamma doses from cloud
Gamma doses from cloud
Gamma doses from ground
Gamma doses from ground
Doses from inhalation
Doses from inhalation
Fig. 20.7
Scheme for calculating dose rates and doses (as function of space and time, specific for
organs and nuclides)
summarized as so-called “dose factors” and are available from various radiation
protection institutions. With such dose factors, the ground gamma dose rate for
example can be obtained with the following simple equation:
m
2
Dose rate Sv
ð
=
h
Þ¼
Dose rate factor Sv
ð
=
h
Þ=
Bq
=
:
m
2
soil contamination Bq
=
If the soil contamination is known, the dose rate factor allows direct calculation
of the dose rate. The dose rate factor for cesium-137, e.g., is approximately
2.5
10
12
(Sv/h)/(Bq/m
2
). A soil contamination of 10
6
Bq/m
2
of Cs-137 then
results in an exposure rate of 2.5
Sv/h.
The local dose rate is calculated as the sum of the dose rate from the soil and the
dose rate from the cloud near to the ground.
Besides the dose rate factors, there are also dose factors for ground irradiation.
They are used for calculating doses over longer exposure times, i.e. the time spent
on the contaminated ground surface. Ground dose rate and dose factors are nuclide-
specific and include radioactive decay, ground dose factors also the absorption
resulting from radioactive nuclides penetrating into the soil.
The uptake of radionuclides by inhalation of air from the cloud near ground or
from resuspension depends on the breathing rate and the inhalation time period.
Once in the lungs, the complex transport of the radionuclides within the body, the
effects of the internal irradiation in the body organs, and the resulting dose
commitment is calculated with complicated models and summarized as nuclide-
and organ dependent dose factors for various age groups. The organ doses are then
obtained by multiplying the activity intake (Bq) by inhalation with the organ-
specific dose inhalation dose factor (Sv/Bq).
μ
