Internal dosimetry
Internal dosimetry is the science and art of internal ionising radiation dose assessment due to radionuclides incorporated inside the human body.
Radionuclides deposited within a body will irradiate tissues and organs and give rise to committed dose until they are excreted from the body or the radionuclide is completely decayed.
The internal doses for workers or members of the public exposed to the intake of radioactive particulates can be estimated using bioassay data such as lung and body counter measurements, urine or faecal radioisotope concentration, etc. The International Commission on Radiological Protection (ICRP) biokinetic models are applied to establish a relationship between the individual intake and the bioassay measurements, and then to infer the internal dose.
The internal radiation dose due to ingested or inhaled radioactive substances is known as committed dose.
The ICRP defines Committed effective dose, E(t) as the sum of the products of the committed organ or tissue equivalent doses and the appropriate tissue weighting factors WT, where t is the integration time in years following the intake. The commitment period is taken to be 50 years for adults, and to age 70 years for children.
The ICRP further states "For internal exposure, committed effective doses are generally determined from an assessment of the intakes of radionuclides from bioassay measurements or other quantities (e.g., activity retained in the body or in daily excreta). The radiation dose is determined from the intake using recommended dose coefficients".
There are a few routes of intake (of radionuclide) namely,
In an radioactive area, radionuclide particulate may be suspended in the air and can enter the body by inhalation. These particulates may be deposited in different parts of the respiratory tract depending upon their aerodynamic diameter.
In-vivo monitoring
Internal dose monitoring of the radionuclides which emit radiation which can penetrate out of the body. For example X-rays, gamma rays of sufficient energy. It can be measured by devices such as a whole body counter.
A whole body counter has a low background arrangement with counting systems
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