Equivalent dose, committed equivalent dose and sievert

Equivalent dose (HT): dose absorbed by the tissue or organ T, weighted according to the type and energy of the radiation R. It is given by the following formula:

                               HT,R = wR DT,R

where
DT,R is the mean for the organ or tissue T of the absorbed dose of radiation R;
wR is the weighting factor for radiation R;.
When the radiation field comprises radiation of types and energies corresponding to different values of wR the total equivalent dose HT is given by the formula:

                               HT =∑wR DT,R

The equivalent dose unit is the sievert (Sv). &

The ICRP's wR values, published in the order of 1st September 2003, are given in the following table. For the types of radiation which do not appear in the table, an approximate wR value is obtained from the mean quality factor determined by the ICRU.

Type of radiation and energy range
wR
Photons all energies
1
Electrons and muons all energies
1
Neutrons of less than 10 keV
5
Neutrons from 10 to 100 keV
10
Neutrons from 100 keV to 2 MeV
20
Neutrons from 2 MeV to 20 MeV
10
Neutrons of more than 20 MeV
5
Protons of more than 2 MeV
5
Alpha particles
20

Committed equivalent dose [HT(τ)]: integral over time (τ) of the equivalent dose rate in the tissue or organ T to be received by an individual following the intake of radioactive material. For an intake or activity at time to, it is defined by the formula:

                                                to +τ
                              HT(τ) = ∫ HT (t) dt
                                                to

where
HT (t) is the equivalent dose rate in the organ or tissue T at time t,
τ the period over which intake is carried out.
In HT(τ), τ is given in years. If the value of τ is not given, for adults it is implicitly taken at fifty years and for children as the number of years remaining until the age of 70.

The committed equivalent dose unit is the sievert (Sv).
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