Measuring radioactivity – converting doses

Facts and Information about Radiation Exposure The Energy Collective,

The external radiation dose, such as from soil, air, water and food, in Bqs, can be measured using appropriate instrumentation. The Bqs measured are much greater than the Gys encountered by a person because of personal protection and distance from the radiation source; the intensity of radiation is reduced by the square of the distance from the source.

Dose conversion factors, DCFs, have been calculated using computer programs by the various government agencies. The DCFs take into account the energy of multiple isotopes, multiple exposure events, isotope residence times, radioactive daughters, tissue types, distance from the source, etc. DCFs (units Sv/Bq) are used to convert the Bqs to Svs.

Because DCFs exist for all radionuclides, the total Sv dose received from all radionuclides taken into the body during a year or a lifetime can be calculated and compared with public Sv dose limits set by government agencies. The website below has several examples using Bqs and DCFs to calculate Svs for ingestion, inhalation and immersion.

Click to access H49-96-1-1995E-2.pdf

Click to access 520-1-88-020.pdf


Absorbed Dose: Gy is a unit of ionizing radiation dose absorbed by biological matter, either through the skin, inhaled or ingested.

To gauge biological effects the Absorbed Dose is multiplied by weighing factor We, which is dependent on the type of ionizing radiation. Such measurement of biological effect is called “Equivalent Dose” and is measured in Sv.

Equivalent Dose = Gy x energy weighing factor We = Sv

For x-rays, gamma rays, electrons, positrons, muons: We = 1, and 1 Gy x 1 = 1 Sv

For neutrons of different energy levels: We varies from 5 to 20, and 1 Gy varies from 5 to 20 Sv

For alpha particles, fission fragments, heavy nuclei: We = 20, and 1 Gy x 20 = 20 Sv

Example: The Equivalent Dose of mixed radiation may be 0.3 mGy x (We = 5, slow neutron) + 6 mGy x (We = 1, gamma rays) + 0.1 mGy x (We = 20, fast neutron) = 9.5 mSv

To gauge biological effects the Equivalent Dose is multiplied by weighing factor Wt, which is dependent on the tissue type. Such measurement of biological effect is called “Effective Dose” and is measured in Sv.

Effective Dose = Gy x We x tissue weighing factor Wt = Sv

For bone surface, skin: Wt = 0.01

For bladder, breast, liver, esophagus, thyroid: Wt = 0.05

For bone marrow, colon, lung, stomach: Wt = 0.12

For gonads (testes, ovaries): Wt = 0.20

Example: The above calculated Effective Dose for a bladder may be 9.5 mSv x (Wt = 0.05, bladder) = 0.475 mSv

During an X-ray test, the dense bone tissue absorbs radiation energy causing some instant ionizing damage, such as creating free radicals inside bones, whereas the radiation energy easily passes through the less dense fleshy tissues to the film in old X-ray systems, to the digital sensor in new X-ray systems.

Ingestion and inhalation of radioactive particles cause much greater ionizing damage to body tissues for longer periods of time than high energy electromagnetic waves, such as X-rays. …

One Response to “Measuring radioactivity – converting doses”

  1. Martin Kral Says:

    Forgot to edit the above comment. Please excuse the spelling and grammar errors.

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