Radiation Protection Glossary

A radiation protection glossary for Radiation Protection Supervisors (RPS), Radiation Protection Advisers (RPA) and anyone else interesting in radiation safety terms and definitions. The glossary is a mixture of health physics , phrases related to radiation protection legislation, transport, practical safety, technical terms and similar.

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Accumulated dose (cumulative dose)

Accumulated dose (cumulative dose) is the total radiation dose accumulated over a defined period such as minute, hour or year. Its value can be used operationally (i.e. for a particular task working with ionising radiation), or may be defined in terms of a dose constraint or annual legal dose limit. Generally accumulated dose requires a dose rate (exposure per unit time) and an exposure duration (time) such that:

\[ Accumulated\;Dose=Dose\; rate(\frac{Dose}{Time})\times Duration(Time)\]

Often this is easy to understand and measure such as:

  • Measuring the accumulated dose from a static radioactive source with a fixed dose rate and distance (over a certain period of time.
  • Measuring the accumulated dose from a static x-ray generator with a fixed dose rate and distance (over a certain period of time).

The above are quite easy to calculated with simple maths and using simple concepts such as the inverse square law.

If the dose rate and / or distance is changing (per unit time) than the accumulation can still be measured simply with a suitable integrating radiation measurement device. If no such monitor is available and you wish to calculate the dose (with a changing dose rate) you have to use more in-depth mathematical analysis and perhaps a computer model. However, sometimes complicated maths can be distilled down into quite simple expressions, an example of this is found here: The accumulated radiation dose when moving up to a source.

Accumulated dose to the whole body and / or extremities can be measured with a passive dosimeter or active dosimeter).

Accumulated dose from the intake of radioactive material (via inhalation or ingestion etc) is more difficult to determine and will usually require a combination of biological dosimetry (e.g. urine / blood), perhaps combined with environmental or personal air sampling, and the use of computer based dosimetric models. In this case accumulated dose is stated as the total dose accumulated in the year of intake, even though the total does uptake might be over a longer period (this depends on the radioactive half life and biological half-life of the material taken into the body).

In radiation protection I spend most of my time explaining to clients what they do not need to worry about.

– Mark Ramsay -