Ionizing Radiation - Measurement


The human body cannot sense ionizing radiation, but the effects of ionization can be used to characterize the radiation. Parameters of interest include disintegration rate, particle flux, particle type, beam energy, kerma, dose rate and cummulative dose received by a target. Particle type is determined by differential measurements in the presence of electrical fields, magnetic fields, or varying amounts of shielding. Dose values may represent absorbed, equivalent, effective, or committed dose. The monitoring and calculation of doses to safeguard human health is called dosimetry.

Quantity Particle detector CGS units SI units Other units
Disintegration rate curie becquerel
Particle flow rate geiger counter, proportional counter, scintillator counts per minute
Fluence thermoluminescent dosimeter, Film badge dosimeter joule/metre2
Beam energy proportional counter electronvolt joule
Kerma ionization chamber, semiconductor detector, quartz fiber dosimeter, Kearny Fallout Meter esu/cm3 coulomb/kilogram roentgen
Absorbed dose calorimeter rad gray rep
Equivalent dose derived quantity rem sievert
Effective dose derived quantity rem sievert BRET
Committed dose derived quantity rem sievert banana equivalent dose

Radiation measuring instruments are commonly calibrated to provide readouts of more sophisticated quantities than what is actually measured. For example, most dosimeter give instantaneous readouts of equivalent dose or even effective dose, even though the directly measured quantity is actually fluence or sometimes kerma. Such calibrations make assumptions about the radiation type, beam energy, field uniformity, and penetrating power based on the expected use of the instrument. These assumptions are not universally applicable, and may produce very erroneous readings in some situations.

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