Civil Engineering Reference
In-Depth Information
Table 4.1
Radiation weighting factor, w
R
, according to ICRP 60 [
5
] and ICRP 103 [
7
]
ICRP 60 [5]
Radiation weighting factor
(w
R
)
ICRP 103 [7]
Radiation weighting factor
(w
R
)
Type and energy of radiation
Photons (all energies)
1
1
Electrons, Muons (all energies)
Neutrons
1
(Multiple step function)
1
(Continuous function)
(See [7])
<
10 keV
5
10 keV to 100 eV
10
>
100 keV to 2 MeV
20
>
2 MeV to 20 MeV
10
>
20 MeV
5
Protons
>
2 MeV
5
2
Alpha particles, fission fragments,
heavy nuclei
20
20
dose”. The “effective dose” is the sum total of the equivalent doses in all organs
(tissues) of the body weighted by the tissue weighting factors,
X
effective dose
¼
w
T
H
T
T
where
H
T
≙
equivalent dose in the organ (tissue),
w
T
¼
organ weighting factor for tissue, T.
4.3 Natural Background Radiation
All individuals are exposed to natural background radiation, which consists of
cosmic radiation, external terrestrial radiation from naturally radioactive isotopes
in the soil and rocks or houses and internal radiation after inhalation and ingestion
of naturally radioactive isotopes in the human body.
The mean natural background whole body dose on earth is 2.4 mSv/year.
Accordingly, the average lifetime dose (70 years) is about 170 mSv.
The average background whole body dose in the USA is about 3.7 mSv/year
(medical X-rays excluded). It varies with altitude, geographic location, etc. In
Kerala, India, or in Brazil with large monazite reserves (thorium), the background
