# S coefficient (radiation weighted)

The equivalent dose to target region [math]r_T[/math] per nuclear transformation of a given radionuclide in source region [math]r_S[/math], Sv (Bq s)^{-1}.

[math] S_w(r_T \leftarrow r_S) = \sum_R w_R \sum_i E_{R,i} Y_{R,i} \phi (r_T \leftarrow r_s, E_{R,i}) [/math]

where [math]E_{R,i}[/math] is the energy in joules of the i^{th} radiation of type [math]R[/math] emitted in nuclear transformations of the radionuclide (J); [math]Y_{R,i}[/math] is the yield of the i^{th} radiation of type [math]R[/math] per nuclear transformation [(Bq s)^{-1}]; [math]w_R[/math] is the radiation weighting factor for radiation type [math]R[/math]; and [math]\phi (r_T \leftarrow r_s, E_{R,i})[/math] is the speciﬁc absorbed fraction deﬁned as the fraction of energy [math]E_{R,i}[/math] of radiation type [math]R[/math] emitted within the source region [math]r_S[/math] that is absorbed per mass in the target region [math]r_T[/math] (kg^{-1}).

ICRP Publication 130, 2015

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