(Art. 2 para. 2 let. b, Art. 22, Art. 61 para. 1 and Art. 194 para. 3)
The fundamental dose quantity given by:
whereis the mean energy imparted to matter of mass dm by ionising radiation. The SI unit for absorbed dose is joule per kilogram (J/kg), and its special name is gray (Gy).
The absorbed doseD T, averaged over the tissue or organ T, which is given by:
whereis the mean total energy imparted in a tissue or organ T, andis the mass of that tissue or organ.
The dose in a tissue or organ T given by:
whereD T.Ris the mean absorbed dose from radiation R in a tissue or organ T, andw Ris the radiation weighting factor. Sincew Ris dimensionless, the unit for the equivalent dose is the same as for absorbed dose, J/kg. Its special name is sievert (Sv).
| Radiation type and energy range | Radiation weighting factor, w | |
|---|---|---|
| Photons, all energies | 1 | |
| Electrons and muons, all energies | 1 | |
| Neutrons, energy | – under 1 MeV – 1 MeV–50 MeV – over 50 MeV | 2,5+18,2·e-[ln(E)]²/6 5,0+17,0·e-[ln(2·E)]²/6 2,5+3,25·e-[ln(0,04·E)]²/6 |
| Protons and charged pions | 2 | |
| Alpha particles, fission fragments, heavy nuclei | 20 |
The time integral of the equivalent dose rate in a particular tissue or organ that will be received following intake of radioactive material into the body by a Reference Person, where τ is the integration time in years.
The tissue-weighted sum of the equivalent doses in all specified tissues and organs of the body, given by the expression:
whereH Torw RD T.Ris the equivalent dose in a tissue or organ T andw Tis the tissue weighting factor. The unit for the effective dose is the same as for absorbed dose, J/kg, and its special name is sievert (Sv).
| Tissue or organ | Tissue weighting factor, w |
|---|---|
| Bone-marrow (red) | 0.12 |
| Colon | 0.12 |
| Lung | 0.12 |
| Stomach | 0.12 |
| Breast | 0.12 |
| Gonads | 0.08 |
| Bladder | 0.04 |
| Liver | 0.04 |
| Oesophagus | 0.04 |
| Thyroid | 0.04 |
| Brain | 0.01 |
| Skin | 0.01 |
| Bone surface | 0.01 |
| Salivary glands | 0.01 |
| Remainder tissues | 0.12 |
The sum of the products of the committed organ or tissue equivalent doses and the appropriate tissue weighting factors (w T), where τ is the integration time in years following the intake. The commitment period is taken to be 50 years for adults, and up to age 70 years for children.
1.9.1 The product ofD andQ at a point in tissue, whereD is the absorbed dose andQ is the quality factor for the specific radiation at this point, thus:
1.9.2 The unit of dose equivalent is joule per kilogram (J/kg), and its special name is sievert (Sv). For the relevant operational quantities, see personal dose equivalent and ambient dose equivalent.
The dose equivalent measured at a specific location. The quantities ambient dose equivalentH** (10) and directional dose equivalentH'* (d , Ω) are taken to be the ambient dose.
1.11.1 One dose equivalent: the dose equivalent in soft tissue (commonly interpreted as the «ICRU sphere») at an appropriate depth,d [mm], below a specified point on the human body, usually given by the position where the individual’s dosimeter is worn. The unit of personal dose equivalent is joule per kilogram (J/kg), and its special name is sievert (Sv).
1.11.2 The personal dose equivalentH p(10) is used as an estimate of the effective dose. The personal dose equivalentH p(0.07) is used as an estimate of the dose to the skin and to the lens of the eye. Alternatively, the personal dose equivalentH p(3) may be used as an estimate of the dose to the lens of the eye.
1.12.1 The dose equivalent at a point in a radiation field that would be produced by the corresponding expanded field in the ICRU sphere at a depth,d , on a radius in a specified direction, Ω. The unit of directional dose equivalent is joule per kilogram (J/kg), and its special name is sievert (Sv). 1.12.2 In the particular case of a unidirectional field, the direction can be specified in terms of the angle α between the radius opposing the incident field and the specified radius Ω. If α= 0°, the quantityH' (d , 0°) may be written asH' (d ) and is equal toH** (d ). 1.12.3 The recommended values ford* are 10 mm for penetrating radiation, 0.07 mm for low-penetrating radiation and 3 mm for the lens of the eye (see operational quantities for area monitoring ).
The dose equivalent at a point in a radiation field that would be produced by the corresponding expanded and aligned field in the ICRU sphere at a depth of 10 mm on the radius vector opposing the direction of the aligned field. The unit of ambient dose equivalent is joule per kilogram (J/kg), and its special name is sievert (Sv).
A sphere of tissue-equivalent material, 30 cm in diameter, with a density of 1 g/cm3and a mass composition of 76.2% oxygen, 11.1% carbon, 10.1% hydrogen and 2.6% nitrogen.
1.15.1 The factor characterising the biological effectiveness of a radiation, based on the ionisation density along the tracks of charged particles in tissue.Q is defined as a function of the unrestricted linear energy transfer, LET (L in keV/μm), of charged particles in water:
1.15.2 Q has been superseded by the radiation weighting factor,w R, in the definition of equivalent dose, but it is still used in calculating the operational dose equivalent quantities used in monitoring.
The effective dose and equivalent doses are generally determined using operational quantities.
2.2.1 The operational quantities for individual monitoring of external exposure are:
2.2.2 The operational quantities for area monitoring are:
a. the ambient dose equivalentH** (10); b. the directional dose equivalentH'* (0.07);
c. the directional dose equivalentH' (3).
2.2.3 The operational quantity for internal exposure is the committed effective doseE 50, calculated using standard models and the dose coefficients specified in Annexes 3 and 6.
2.3.1 In situations of external exposure, the equivalent dose for organs is taken to be equal to the personal dose equivalentH p(10), or to the ambient dose equivalentH (10), for all tissues and organs apart from the skin and the lens of the eye.
2.3.2 In situations of external exposure, the equivalent dose for the skin, hands and feet is taken to be equal to the personal dose equivalentH* p(0.07), or to the directional dose equivalentH' (0.07).
2.3.3 In situations of external exposure, the equivalent dose for the lens of the eye is taken to be equal to the personal dose equivalentH p(0.07), or to the directional dose equivalentH' (0.07). Alternatively, it may also be taken to be equal to the personal dose equivalentH p(3), or to the directional dose equivalentH' (3).
2.3.4 The effective dose is taken to be equal to the sum of:
a. the personal dose equivalentH p(10), or the ambient dose equivalentH** (10); and
b. the committed effective doseE* 50.
If the dose values determined in accordance with point 2.3 are above the relevant limits, then the effective dose or equivalent doses for the person concerned must be individually determined by a radiological protection expert, in cooperation with the supervisory authority, using calculation methods and dose coefficients in accordance with the current state of science and technology. The value thus determined is decisive in establishing whether or not a dose limit has been exceeded.
Where ambient dose limits are specified by this Ordinance, the ambient dose is taken to be: a. the quantityH** (10) (ambient dose equivalent) for penetrating radiation; b. the quantityH'* (0.07) (directional dose equivalent) for low-penetrating radiation.
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