# Radiation weighting factors

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Radiation Weighting Factor, wR

The radiation weighting factor is a dimensionless factor used to obtain the equivalent dose from the absorbed dose averaged over a tissue or organ and is based on the type of radiation absorbed. The most recent values (from ICRP 103 (2007)) of the radiation weighting factors are shown in the table below.

  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 continous function of neutron energy     (see Fig. 1 and Eq. 1) 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).

The following continuous function in neutron energy $E_n \text { (MeV)}$ is recommended for the calcullation of radiation weighting factors for neutrons: $w_R = \begin{cases}

2.5 + 18.2e^{-[ln (E_n)]^2/6}, & \text{if } E_n < 1 \text{ MeV} \ 5.0 + 17.0e^{-[ln (2E_n)]^2/6}, & \text{if } 1 \text{ MeV} \le E_n \le 50 \text{ MeV} \\ 2.5 + 3.25e^{-[ln (0.04E_n)]^2/6}, & \text{if } E_n > 50 \text{ MeV} \
\end{cases}$ $(Eq.~1)$ Fig. 1. Radiation weighting factor, wR for neutrons versus neutron energy

See also Equivalent dose