Equivalent dose, H

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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.

H_{T,R} = w_R · D_{T,R}

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, H_T is the sum of HT,R over all radiation types i.e.

H_T=\Sigma_R H_{T,R}

Recommended radiation weighting factors from ICRP 103 (2007)
  Radiation type   Radiation weighting factor, wR
  Photons   01
  Electronsa and muons     01
  Protons and charged pions   02
  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).

See also Radiation weighting factors, Effective dose, E


ICRP 103 (2007)

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