Blog #9 Units of Exposure and Biological Effects

Blog 9: Units of Exposure and Biological Effects

“Ionizing radiation is emitted when radioactive substances decay. Radioactive decay occurs when the nucleus of an atom spontaneously decays by emitting a particle (an alpha particle, an electron, or one or more neutrons).

The four forms of ionizing radiation are alpha particles, beta particles, gamma rays, and, indirectly, neutrons. All have enough energy to ionize atoms, in other words, remove one or more of the atom’s electrons.”

-    http://ieer.org/resource/classroom/measuring-radiation-terminology/

“Beyond certain thresholds, radiation can impair the functioning of tissues and/or organs and can produce acute effects such as skin redness, hair loss, radiation burns, or acute radiation syndrome. These effects are more severe at higher doses and higher dose rates.”

-    http://www.who.int/mediacentre/factsheets/fs371/en/

There are four measures of radiation commonly encountered when dealing with the biological effects of Ionizing Radiation. Exposure, Dose, Dose Equivalent, and Dose Rate.

Exposure:  measures the strength of a radiation field, the roentgen aka ‘R’ indicates the degree of ionization a particle is capable of producing.

Dose or Absorbed Dose:  The dose is the amount of radiation absorbed by an object. Measured in ‘Gy’ (gray), however the ‘rad’ (Radiation Absorbed Dose) is more commonly used. 1 rad is equal to 0.01 Gy. Different materials can absorb the same amount of radiation differently. In the case of human tissue, one Roentgen of gamma radiation results in one rad of absorbed dose.

Dose Equivalent:  The dose equivalent draws a comparison to the absorbed dose and the resulting biological effects. The absorbed dose of specific types of radiation is then multiplied by a "quality factor" to get the dose equivalent. Measured in SV (sievert), but the rem ‘roentgen equivalent in man’ is more commonly used. One rem is equivalent to 0.01 SV. When exposed to X- or Gamma radiation, the quality factor is 1.

Dose Rate: Measure the rate radiation dose is received. Dose rate is usually depicted in terms of R/hour, mR/hour, rem/hour, mrem/hour, etc.

People are exposed to natural sources of ionizing radiation, such as in soil, water, vegetation, and in human-made sources, such as x-rays and medical devices. Ionizing radiation has many beneficial applications, including uses in medicine, industry, agriculture and research. Low doses of ionizing radiation can increase the risk of longer term effects such as cancer.

Biological effects of RAD:

0-25 No observable effect.

25-50       Minor temporary blood changes.

50-150 Nausea and vomiting and reduced WBC.

150-300 Increased reaction of above as well as diarrhea, malaise, loss of appetite even death.

300-500 Increased reaction of above and hemorrhaging.

500+

Cancer, leukemia, cataracts, and miscarriage. Genetic effects to children of exposed persons will occur and almost always harmful. Organs like lymphocytes, bone marrow, gastro-intestinal, gonads, and other fast-growing cells will be damaged by the exposure.