Dose 20


Dose 20 :

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 Radiation 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: (1) Dose Equivalent: The dose equivalent is the product of the absorbed dose in ICRU →soft tissue and the →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. (2) 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. (3) Absorbed 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: D = dἒ / dm. 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. (4) 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(τ) for incorporation at time t0 is the time integral of the organ dose rate in the tissue or organ T. (5) 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. (6) 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. HT,R = WR DT,R. If the radiation consists of types and energies with different wR values, the individual values are added. HT = ΣRWR DT,R. (6) 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. (7) Personal dose: The Radiation 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. (8) Directional dose equivalent: The directional dose equivalent H'(0.07, Ω) 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 which is oriented in the fixed direction Ω. (9) Personal dose equivalent: The personal dose equivalent Hp(10) is the dose equivalent at a body depth of 10 mm at the point of application of the personal dosimeter. (10) Ambient dose equivalent: The ambient 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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