External and Internal Exposures
The assessment of dose from exposure to radiation from external sources is usually done by the use of personal dosimeters or from the measurement or evaluation of the ambient dose equivalent, #*(10). The ambient dose equivalent at a point in a radiation field is the dose equivalent to that would be produced by the corresponding expanded and aligned field in the ICRU sphere at a depth of 10 mm on the radius opposing the direction of the aligned field (ICRP, 2007). If the radiation field is known (point source, cloud immersion, surface contamination, etc.), #*(10) can be estimated using conversion coefficients (ICRP, 2007). Regarding decay types, the external dose arises primarily from у-emitting radionuclides, and secondarily from exposure to neutrons and р-particles to the skin. The influence of a-emitting radionuclides to the external exposure can be considered negligible, save for some very special cases, as a geometry extremely close to the eye.
The internal exposure comprises the intake of radionuclides by inhalation and ingestion. The committed effective dose from internal exposure is assessed by the following equation
where e_{jmh} is the dose effective coefficient for the inhalation intake of radionuclide j, /,,_{nh} is the activity intake of radionuclide j by inhalation, e_{j ing} is the dose effective coefficient for the ingestion intake of radionuclide j, and Ij_{inh} is the activity intake of radionuclide j by ingestion. The inhalation and ingestion dose coefficients for members of the public are age dependent. There are five age groups for children and one for adults. The inhalation dose coefficients are calculated assuming that clearance from the respiratory tract and absorption into blood is independent of age and sex. For particulate aerosols, an activity mean aerodynamic diameter (AMAD) of 1 pm was used. Daily air intake, averaged over a 24-h period, was taken to be 2.9, 5.2, 8.7, 15, 20, and 22 m^{3} for the 3-month- old infant, 1-, 5-, 10-, and 15-year-old children, and adult, respectively (ICRP, 2012). Ingestion dose coefficients are calculated using higher gastrointestinal absorption factor (/,) values for 3-month- old infants than older individuals. For most elements, adult values are applied to 1-, 5-, 10-, and 15-year-old children. However, intermediate values are used for children in the cases of calcium, iron, cobalt, strontium, barium, lead, and radium (ICRP, 2012). The incorporation of radionuclides through other events, such as w'ounds, is not considered in this approach (ICRP, 2007). Tables 7.3 and 7.4 show some dose coefficients for inhalation and ingestion, respectively (ICRP, 2012). It can also be observed that the dose coefficients for а-emitting radionuclides are higher than those у-emitters, due to the short range in which a-particles deposit their energy. Therefore, a-emitting radionuclides, such as ^{238}U, ^{226}Ra, ^{2W}Po, ^{232}Th, among others, are usually the main contributors to internal exposure.
Table 7.3 Inhalation Dose Coefficients for Members of the Public, e_{inh}, Expressed in Sv/Bq for Different Group Ages
Nuclide |
Tv, |
e_{inh} (Sv/Bq) (AMAD = 1 цт) |
||||||
Type |
<1 year |
1 year |
5 years |
10 years |
15 years |
Adult |
||
“Al |
7.16E5 years |
F |
8.1E-08 |
6.2E-08 |
3.2E-08 |
2.0E-08 |
1.3E-08 |
1.1E-08 |
M |
8.8E-08 |
7.4E-08 |
4.4E-08 |
2.9E-08 |
2.2E-08 |
2.0E-08 |
||
«к |
1.28E9years |
F |
2.4E-08 |
1.7E-08 |
7.5E-09 |
4.5E-09 |
2.5E-09 |
2.1E-09 |
^{M}Mn |
312.5 days |
F |
5.2E-09 |
4.1E-09 |
2.2E-09 |
1.5E-09 |
9.9E-10 |
8.5E-10 |
M |
7.5E-09 |
6.2E-09 |
3.8E-09 |
2.4E-09 |
1.9E-09 |
1.5E-09 |
||
^{59}Fe |
44.529 days |
F |
2.1E-08 |
1.3E-08 |
7.1E-09 |
4.2E-09 |
2.6E-09 |
2.2E-09 |
M |
1.8E-08 |
1.3E-08 |
7.9E-09 |
5.5E-09 |
4.6E-09 |
3.7E-09 |
||
s |
1.7E-08 |
1.3E-08 |
8.1E-09 |
5.8E-09 |
5.1E-09 |
4.0E-09 |
||
“Co |
70.80 days |
F |
4.0E-09 |
3.0E-09 |
1.6E-09 |
1.0E-09 |
6.4E-10 |
5.3E-10 |
M |
7.3E-09 |
6.5E-09 |
3.5E-09 |
2.4E-09 |
2.0E-09 |
1.6E-09 |
||
s |
9.0E-09 |
7.5E-09 |
4.5E-09 |
3.1E-09 |
2.6E-09 |
2.1E-09 |
||
“Co |
5.271 years |
F |
3.0E-08 |
2.3E-08 |
1.4E-08 |
8.9E-09 |
6.1E-09 |
5.2E-09 |
M |
4.2E-08 |
3.4E-08 |
2.1E-08 |
1.5E-08 |
1.2E-08 |
1.0E-08 |
||
s |
9.2E-08 |
8.6E-08 |
5.9E-08 |
4.0E-08 |
3.4E-08 |
3.1E-08 |
||
“Ni |
96 years |
F |
2.3E-09 |
2.0E-09 |
1.1E-09 |
6.7E-10 |
4.6E-10 |
4.4E-10 |
M |
2.5E-09 |
1.9E-09 |
1.1E-09 |
7.0E-10 |
5.3E-10 |
4.8E-10 |
||
s |
4.8E-09 |
4.3E-09 |
2.7E-09 |
1.7E-09 |
1.3E-09 |
1.3E-09 |
||
“Sr |
29.12 years |
F |
1.3E-07 |
5.2E-08 |
3.1E-08 |
4.1E-08 |
5.3E-08 |
2.4E-08 |
M |
1.5E-07 |
1.1E-07 |
6.5E-08 |
5.1E-08 |
5.0E-08 |
3.6E-08 |
||
s |
4.2E-07 |
4.0E-07 |
2.7E-07 |
1.8E-07 |
1.6E-07 |
1.6E-07 |
||
^{l10m}Ag |
249.9 days |
F |
3.5E-08 |
2.8E-08 |
1.5E-08 |
9.7E-09 |
6.3E-09 |
5.5E-09 |
M |
3.5E-08 |
2.8E-08 |
1.7E-08 |
1.2E-08 |
9.2E-09 |
7.6E-09 |
||
s |
4.6E-08 |
4.1E-08 |
2.6E-08 |
1.8E-08 |
1.5E-08 |
1.2E-08 |
||
1311 |
8.04 days |
F |
7.2E-08 |
7.2E-08 |
3.7E-08 |
1.9E-08 |
1.1E-08 |
7.4E-09 |
M |
2.2E-08 |
1.5E-08 |
8.2E-09 |
4.7E-09 |
3.4E-09 |
2.4E-09 |
||
s |
8.8E-09 |
6.2E-09 |
3.5E-09 |
2.4E-09 |
2.0E-09 |
1.6E-09 |
||
^{137}Cs |
30.0 years |
F |
8.8E-09 |
5.4E-09 |
3.6E-09 |
3.7E-09 |
4.4E-09 |
4.6E-09 |
M |
3.6E-08 |
2.9E-08 |
1.8E-08 |
1.3E-08 |
1.1E-08 |
9.7E-09 |
||
s |
1.1E-07 |
1.0E-07 |
7.0E-08 |
4.8E-08 |
4.2E-08 |
3.9E-08 |
||
210pb |
22.3 years |
F |
4.7E-06 |
2.9E-06 |
1.5E-06 |
1.4E-06 |
1.3E-06 |
9.0E-07 |
M |
5.0E-06 |
3.7E-06 |
2.2E-06 |
1.5E-06 |
1.3E-06 |
1.1E-06 |
||
s |
1.8E-05 |
1.8E-05 |
1.1E-05 |
7.2E-06 |
5.9E-06 |
5.6E-06 |
||
^{226}Ra |
1600 years |
F |
2.6E-06 |
9.4E-07 |
5.5E-07 |
7.2E-07 |
1.3E-06 |
3.6E-07 |
M |
1.5E-05 |
1.1E-05 |
7.0E-06 |
4.9E-06 |
4.5E-06 |
3.5E-06 |
||
s |
3.4E-05 |
2.9E-05 |
1.9E-05 |
1.2E-05 |
1.0E-05 |
9.5E-06 |
||
232Th |
1.405E10 years |
F |
2.3E-04 |
2.2E-04 |
1.6E-04 |
1.3E-04 |
1.2E-04 |
1.1E-04 |
M |
8.3E-05 |
8.1E-05 |
6.3E-05 |
5.0E-05 |
4.7E-05 |
4.5E-05 |
||
s |
5.4E-05 |
5.0E-05 |
3.7E-05 |
2.6E-05 |
2.5E-05 |
2.5E-05 |
||
238(J |
4.468E9 years |
F |
1.9E-06 |
1.3E-06 |
8.2E-07 |
7.3E-07 |
7.4E-07 |
5.0E-07 |
M |
1.2E-05 |
9.4E-06 |
5.9E-06 |
4.0E-06 |
3.4E-06 |
2.9E-06 |
||
s |
2.9E-05 |
2.5E-05 |
1.6E-05 |
1.0E-05 |
8.7E-06 |
8.0E-06 |
||
239_{Pu} |
24065years |
F |
2.1E-04 |
2.0E-04 |
1.5E-04 |
1.2E-04 |
1.1E-04 |
1.2E-04 |
M |
8.0E-05 |
7.7E-05 |
6.0E-05 |
4.8E-05 |
4.7E-05 |
5.0E-05 |
||
s |
4.3E-05 |
3.9E-05 |
2.7E-05 |
1.9E-05 |
1.7E-05 |
1.6E-05 |
||
^{241} Am |
432.2 years |
F |
1.8E-04 |
1.8E-04 |
1.2E-04 |
1.0E-04 |
9.2E-05 |
9.6E-05 |
M |
7.3E-05 |
6.9E-05 |
5.1E-05 |
4.0E-05 |
4.0E-05 |
4.2E-05 |
||
s |
4.6E-05 |
4.0E-05 |
2.7E-05 |
1.9E-05 |
1.7E-05 |
1.6E-05 |
F, M, and S types indicate fast, medium, and slow absorption (ICRP, 2012).
Table 7.4 Ingestion Dose Coefficients for Members of the Public, e_{lnh}, Expressed in Sv/Bq for Different Group Ages (ICRP, 2012)
Nuclide |
Ту, |
^{e}ing (Sv/Bq) |
|||||
<1 year |
1 year |
5 years |
10 years |
15 years |
Adult |
||
“Al |
7.16E5years |
3.4E-08 |
2.1E-08 |
1.1E-08 |
7.1E-09 |
4.3E-09 |
3.5E-09 |
«к |
1.28E9 years |
6.2E-08 |
4.2E-08 |
2.1E-08 |
1.3E-08 |
7.6E-09 |
6.2E-09 |
^{M}Mn |
312.5 days |
5.4E-09 |
3.1E-09 |
1.9E-09 |
1.3E-09 |
8.7E-10 |
7.1E-10 |
^{59}Fe |
44.529 days |
3.9E-08 |
1.3E-08 |
7.5E-09 |
4.7E-09 |
3.1E-09 |
1.8E-09 |
“Co |
70.80 days |
7.3E-09 |
4.4E-09 |
2.6E-09 |
1.7E-09 |
1.1E-09 |
7.4E-10 |
“Co |
5.271 years |
5.4E-08 |
2.7E-08 |
1.7E-08 |
1.1E-08 |
7.9E-09 |
3.4E-09 |
“Ni |
96 years |
1.6E-09 |
8.4E-10 |
4.6E-10 |
2.8E-10 |
1.8E-10 |
1.5E-10 |
“Sr |
29.12 years |
2.3E-07 |
7.3E-08 |
4.7E-08 |
6.0E-08 |
8.0E-08 |
2.8E-08 |
^{l10m}Ag |
249.9 days |
2.4E-08 |
1.4E-08 |
7.8E-09 |
5.2E-09 |
3.4E-09 |
2.8E-09 |
1311 |
8.04 days |
1.8E-07 |
1.8E-07 |
1.0E-07 |
5.2E-08 |
3.4E-08 |
2.2E-08 |
^{137}Cs |
30.0 years |
2.1E-08 |
1.2E-08 |
9.6E-09 |
1.0E-08 |
1.3E-08 |
1.3E-08 |
210pb |
22.3 years |
8.4E-06 |
3.6E-06 |
2.2E-06 |
1.9E-06 |
1.9E-06 |
6.9E-07 |
^{226}Ra |
1600 years |
4.7E-06 |
9.6E-07 |
6.2E-07 |
8.0E-07 |
1.5E-06 |
2.8E-07 |
232Th |
1.405E10 years |
4.6E-06 |
4.5E-07 |
3.5E-07 |
2.9E-07 |
2.5E-07 |
2.3E-07 |
238(J |
4.468E9 years |
3.4E-07 |
3.4E-07 |
1.2E-07 |
8.0E-08 |
6.8E-08 |
6.7E-08 |
239_{Pu} |
24065 years |
4.2E-06 |
4.2E-06 |
4.2E-07 |
3.3E-07 |
2.7E-07 |
2.4E-07 |
^{241} Am |
432.2 years |
3.7E-06 |
3.7E-07 |
2.7E-07 |
2.2E-07 |
2.0E-07 |
2.0E-07 |