Civil Engineering Reference
In-Depth Information
plutonium may be ingested together with vegetables, milk, meat, fish and drinking
water. Plutonium taken up by way of ingestion is deposited preferably in bone
tissue.
4.2 Radiation Dose
The measure of radiation absorbed is the energy dose [
1
,
5
,
6
]. Historically the unit
was called rad (radiation absorbed dose). It was originally defined as a radiation
dose that deposits 100 erg of energy per gram of absorbing material:
10
5
Joule
100 erg
=
g
=
g
1 rad
≙
≙
To-day, the
absorbed dose
is measured
10
3
Joule
1 Gray Gy
ðÞ¼
100 rad
¼
=
g
¼
1 Joule
=
kg
The biological effects of the radiation dose absorbed also depend on the energy
and type of radiation (
γ
-radiation,
β
-radiation,
α
-particles, neutrons, protons). To
take these differences into account, an equivalent dose was defined. The unit was
called, historically, rem (roentgen equivalent man) and is Sievert (Sv) now
equivalent dose
1 Sievert Sv
ð
≙
100 rem
The absorbed dose and the equivalent dose are related as follows:
ðÞ¼
ðÞ
equivalent dose H Sv
absorbed energy dose Gy
radiation weighting factor w
ðÞ
The radiation weighting factor, w
R
, (Table
4.1
) is a measure of the relative
effects of the nuclear particles in producing damage for a given energy deposition.
It is defined by the International Commission on Radiation Protection (ICRP). For
most of the
-radiations (photons or electrons) of fission products the
radiation weighting factor can be taken as unity. For neutrons the radiation
weighting factor depends on the neutron kinetic energy and varies between 2.5
and 20. (The radiation weighting factors for neutrons vary slightly between ICRP
60 (1991) [
5
] (step function) and ICRP 103 (2007) [
7
] (piecewise linear functions).
For protons with an energy of
γ
- and
β
2 MeV the radiation weight factor is 5 in ICRP
60 [
5
] and 2 in ICRP 103 [
7
]. For alpha-particles entering the body and accumu-
lating in certain tissues the radiation weighting factor is 20 according to both ICRP
Publication 60 (1991) [
5
] and ICRP 103 (2007) [
7
].
To express the different sensitivities of organs, so-called tissue weighting fac-
tors, w
T
, have been introduced (see Table
4.2
). This gives rise to the “effective
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