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Dose

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Measure of a radiation effect to be indicated more precisely. The absorbed dose indicates the total radiation energy absorbed by the irradiated matter in gray (Gy). Central dose variables in radiation protection are "organ dose" and "effective dose". The term "body dose" is used as a collective term for organ dose and effective dose. The latter two are protective variables in radiation protection, including risk assessment. They form a basis for the assessment of the probability of stochastic radiation effects for absorbed doses far below the thresholds for deterministic radiation damage. The unit of these dose values is sievert, symbol: Sv.

The Radiological Protection Ordinance requires measurement of the personal dose for the determination of the body dose which cannot be measured directly. Personal dose is the dose equivalent measured in the measuring variables of depth dose and skin dose at an area of the body surface representative of radiation exposure. The depth dose Hp(10) in this case is an estimated value for the effective dose for whole body exposure with penetrating radiation and the organ doses of deep organs and the skin dose Hp(0,07) are an estimated value for the skin dose.

The dose variables used in radiation protection in more detail:

  • Dose equivalent

    The dose equivalent is the product of the absorbed dose in ICRU (see 'Soft tissue' and 'Quality factor'). In the case of several radiation types and radiation energies the total dose equivalent is the sum of its determined individual amounts. The unit of the dose equivalent is Sievert.

  • Effective dose

    The effective dose is the suitable variable to indicate a uniform dose value in case of different exposure of various body parts in order to evaluate the risk of late radiation injuries. The effective dose E is the sum of the average organ doses HT in the individual organs and tissues of the body due to external or internal radiation exposure multiplied by the tissue weighting factors WT.

  • Organ

    Tissue weighting factor wT

    Gonads

    0.20

    Colon

    0.12

    Bone marrow (red)

    0.12

    Lung

    0.12

    Stomach

    0.12

    Bladder

    0.05

    Chest

    0.05

    Liver

    0.05

    Thyroid gland

    0.05

    Oesophagus

    0.05

    Skin

    0.01

    Bone surface

    0.01

    Pancreas, small intestine, uterus, brain, spleen, muscle, suprarenal gland, kidney, thymus gland

    0.05

     

  • Abbsorbed dose

    The absorbed dose D is the quotient from the average energy transferred to the matter in a volume element by ionizing radiation and the mass of the matter in this volume element:

  • The unit of the absorbed dose is joule divided by kilogram (J·kg-1) and its special unit name is gray (Gy). The former unit name was rad (symbol: rd or rad).1 Gy = 100 rd; 1 rd = 1/100 Gy.

  • Committed dose

    The irradiation of tissue or organs by incorporated radionuclides is distributed over the incorporation period. This period depends upon the physical half-life and the biokinetic behaviour of the radionuclide. The committed dose is the time integral of the dose rate in a tissue or organ over time. The organ committed dose HT() for incorporation at time t0 is the time integral of the organ dose rate in the tissue or organ T. If no integration period is indicated, a period of 50 years for adults and the period from the respective age to the age of 70 years for children are used as a basis:

  • Skin dose

    The skin dose Hp(0.07) is the dose equivalent in 0.07 mm depth in the body at the application point of the personal dosimeter.
    Organ dose

  • Equivalent dose

    The equivalent dose HT,R is the product of the organ absorbed dose DT,R averaged over the tissue/organ T generated by the radiation R and the radiation weighting factor WR.


If the radiation consists of types and energies with different WR values, the individual values are added.

    Radiation type and energy range

    Radiation weighting factor WR

    Photons, all energies

    1

    Electrons and muons, all energies

    1

    Neutrons:

     

    < 10 keV

    5

    10 keV to 100 keV

    10

    >100 keV to 2 MeV

    20

    >2 MeV to 20 MeV

    10

    > 20 MeV

    5

    Protons, except for recoil protons, > 2 MeV

    5

    Alpha particles, fission fragments, heavy nuclei

    20

Radiation weighting factor

  • Local dose

    The local dose is the dose equivalent for soft tissue measured at a certain point. The local dose in the case of penetrating radiation is the ambient dose equivalent; the local dose for radiation with low penetration depth is the directional dose equivalent. The local dose in the case of penetrating radiation is an estimated value for the effective dose and the organ doses of deep organs for radiation with low penetration depth is an estimated value for the skin dose of a person at the place of measurement.

  • Personal dose

    The Radiological Protection Ordinance requires measurement of the personal dose for determination of the body dose. The personal dose is the dose equivalent measured in the measuring variables of depth dose and skin dose at a spot representative of radiation exposure at the body surface. The depth personal dose in the case of whole body exposure to penetrating radiation is an estimated value for the effective dose and the organ doses of deep organs and the skin dose an estimated value for the skin dose.

  • Directional dose equivalent

    The directional dose equivalent H'(0.07,) at the point of interest in the actual radiation field is the dose equivalent which would be generated in the associated expanded radiation field at a depth of 0.07 mm on the radius of the ICRU sphere (see 'ICRU sphere') which is oriented in the fixed direction .

  • Depth dose

    The depth dose Hp(10) is the dose equivalent at a body depth of 10 mm at the point of application of the personal dosimeter.

  • Personal dose equivalent

    The personal dose equivalent H*(10) at the point of interest in the actual radiation field is the dose equivalent which would be generated in the associated oriented and expanded radiation field at a depth of 10 mm on the radius of the ICRU sphere which is oriented opposite to the direction of incident radiation.

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