Dosimetry is the way in which we can quantify the biological effect of radiation on humans.

We can add together different types of radiation of different energies on different tissues and then be able to gauge the total effect on a person.

Absorbed dose

Ionising radiation carries energy. This energy can be absorbed by tissue and possibly cause damage to the tissue.

Absorbed dose (\(D\)) is the energy (\(E\)) absorbed per unit mass (\(m\)) of the absorbing material. The absorbed dose can be calculated by using the following relationship;

\[D = \frac{E}{m}\]

If energy is in joules (\(J\)) and mass is in kilograms (\(kg\)) then the unit of absorbed dose is the gray (\(Gy\)) where one gray is one joule per kilogram.

It is important to use the correct mass of tissue. If the energy is concentrated on a small mass of tissue, the absorbed dose is greater.


A person undergoes a hospital treatment where an organ of mass \(250g\) absorbs \(20J\) of energy. What is the absorbed dose received by the patient?

\[Mass = 250g = 0.25kg\]

\[Energy = 20J\]

\[D = \frac{E}{m}\]

\[D = \frac{{20}}{{0.25}}\]

\[D = 80Gy\]