Section 3 Definitions

Committed effective dose, E(τ)

The quantity 𝐸(𝜏), defined as:

​

where 𝐻T(𝜏) is the committed equivalent dose to tissue or organ T over the integration time 𝜏 elapsed after an intake of radioactive substances and 𝑤T is the tissue weighting factor for tissue or organ T. When 𝜏 is not specified, it will be taken to be 50 years for adults and the time to age 70 years for intakes by children.

Directional dose equivalent, H΄(d,Ω)​

The dose equivalent that would be produced by the corresponding expanded field in the International Commission on Radiation Units and Measurements ICRU sphere at a depth d on a radius in a specified direction Ω.

• - Parameter defined at a point in a radiation field. Used as a directly measurable proxy (i.e. substitute) for equivalent dose in the skin for use in monitoring of external exposure.
• - The recommended value of "d" for weakly penetrating radiation is 0.07 mm

kerma, K

The quantity K, defined as:

where dE_tr is the sum of the initial kinetic energies of all charged ionizing particles liberated by uncharged ionizing particles in a material of mass dm.

• - The SI unit for kerma is joule per kilogram (J/kg), termed the gray (Gy).

air kerma.
The kerma value for air.

• - Under charged particle equilibrium conditions, the air kerma (in grays) is numerically approximately equal to the absorbed dose in air (in grays).
  

reference air kerma rate.

​The kerma rate to air, in air, at a reference distance of 1 m, corrected for air attenuation and scattering.

• - This quantity is expressed in μGy/h at 1 m.
  

Particle fluence, Φ.

A measure of the density of particles in a radiation field, defined as:

where dN is the number of particles incident on a sphere of cross-sectional area da.

Personal dose equivalent, Hp(d)

The dose equivalent in soft tissue below a specified point on the body at an appropriate depth d.

• - Parameter used as a directly measurable proxy (i.e. substitute) for equivalent dose in tissues or organs or (with d = 10 mm) for effective dose, in individual monitoring of external exposure.
• - The recommended values of  "d" are 10 mm for strongly penetrating radiation and 0.07 mm for weakly penetrating radiation for whole body monitoring.
• - Hp(0.07) is used for monitoring for hands and feet for all radiation types.
• - Hp(3) is used for monitoring exposure of the lens of the eye.

-'Soft tissue' is commonly interpreted as the International Commission on Radiation Units and Measurements ICRU sphere.