Radiation dosimetry is the measurement and calculation of the absorbed dose

Absorbed dose

Absorbed dose is a measure of the energy deposited in a medium by ionizing radiation per unit mass...

 in matter and tissue resulting from the exposure to indirect and direct ionizing radiation

Ionizing radiation

Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...

. It is a scientific subspecialty in the fields of health physics

Health physics

Health physics is a field of science concerned with radiation physics and radiation biology with the goal of providing technical information and proper techniques regarding the safe use of ionizing radiation...

 and medical physics

Medical physics

Medical physics is the application of physics to medicine. It generally concerns physics as applied to medical imaging and radiotherapy, although a medical physicist may also work in many other areas of healthcare...

 that is focused on the calculation of internal and external doses from ionizing radiation.

Dose is reported in gray

Gray (unit)

The gray is the SI unit of absorbed radiation dose of ionizing radiation , and is defined as the absorption of one joule of ionizing radiation by one kilogram of matter ....

 (Gy) for matter or sievert

Sievert

The sievert is the International System of Units SI derived unit of dose equivalent radiation. It attempts to quantitatively evaluate the biological effects of ionizing radiation as opposed to just the absorbed dose of radiation energy, which is measured in gray...

s (Sv) for biological tissue, where 1 Gy or 1 Sv is equal to 1 joule

Joule

The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...

 per kilogram.