Equivalent dose, H
Equivalent Dose, HT
The absorbed dose does not give an accurate indication of the harm that radiation can do. Equal absorbed doses do not necessarily have the same biological effects. An absorbed dose of 0.1 Gy of alpha radiation, for example, is more harmful than an absorbed dose of 0.1 Gy or beta or gamma radiation. To reflect the damage done in biological systems from different types of radiation, the equivalent dose is used. It is defined in terms of the absorbed dose weighted by a factor which depends on the type of radiation i.e.
where HT,R is the equivalent dose in tissue T and wR is the radiation weighting factor. The most recent ICRP weighting factors (2007) are given in the table below. The total equivalent dose, is the sum of HT,R over all radiation types i.e.
|Radiation type||Radiation weighting factor, wR|
|Electronsa and muons||1|
|Protons and charged pions||2|
|Alpha particles, fission fragments, heavy ions||20|
|Neutrons|| A continuous function of neutron energy
See Radiation weighting factors
| All values relate to the radiation incident on the body or, for internal radiation sources,
emitted from the incorporated radionuclide(s).
a Note the special issue of Auger electrons discussed in ICRP 103 (2007).