Dose equivalent

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According to ICRU Report 51 the dose equivalent, H, is the product of Q and D at a point in tissue, where D is the absorbed dose and Q is the quality factor at that point, thus

H = Q D.

The unit is J kg-1, the special name for the unit of dose equivalent is sievert (Sv). The quantity dose equivalent is defined for routine radiation-protection applications. It should not be used in the numerical assessment of high-level exposure, for example in radiation accidents.

In 1991 the International Commission on Radiological Protection introduced for dose limitation proposes a quantity called organ dose equivalent, based on the radiation weighting factor w_R and D_T,R the mean absorbed dose in a tissue or organ. Accordingly, the organ equivalent dose H_T,R in a tissue or organ T by the radiation type R is:

H_T,R= W_R^. D_T,R.

In a mixed radiation field the following equation applies for the overall organ equivalent dose H_T in a tissue or organ T:

The unit is joule/kg (J/kg). The special name for the unit of the organ dose is sievert, symbol: Sv. Occasionally the former unit name rem is used. 1 sievert is equal to 100 rem. The quantity organ dose equivalent is only used in radiation protection. These quantity offer a basis for the estimation of stochastic radiation effects (see 'Stochastic radiation effects') for radiation doses far below the threshold values for deterministic radiation effects (see 'Deterministic radiation effects').

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