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Radiation dose

absorbed dose and is measured in units known as grays (Gy).

A gray is an energy liberation of 1 J kg-1 of the material.

Different radiations affect the body more than others so to allow for this a quantity known as the dose equivalent is defined. Each type of radiation has what is known as a relative biological effectiveness (RBE).

Dose equivalent (or effective dose) = radiation dose x RBE

Radiation Relative biological effectiveness (RBE)
beta, gamma, X rays 1
neutrons (slow) 3
alpha 10-20

The unit for the dose equivalent is the sievert (Sv)

The dose equivalent in sievert (Sv) is when the absorbed radiation dose (measured in grays) multiplied by the relative biological effectiveness is 1 Jkg-1. The dose equivalent (or effective dose) is a measure of the likely damage to living tissue. A smaller unit is the millisievert (10-3 Sv).

Different parts of the body react differently to the same radiation dose – bone marrow and lungs being ten times more ‘sensitive’ to radiation damage than skin.

 
 
© Keith Gibbs 2011