The amounts measured in sieverts are intended to represent the stochastic health risk. Radiation dose assessment is defined as the probability of inducing cancer or causing genetic damage.
A sievert carries a 5.5% chance of eventually developing cancer.
Sievert's name comes from the Swedish medical physicist Rolf Maximilian Sievert. Sievert worked on measuring radiation dose in researching the biological effects of radiation.
The equivalent dose is a measure of the radiation dose a tissue receives. It is expressed in sievert.
Attempts have been made to correct the different biological effects of different types of ionizing radiation. The equivalent dose is a less fundamental amount than the absorbed radiation dose, but is biologically more relevant.
The equivalent dose for a tissue is found by multiplying the absorbed dose by a radiation weighting factor. This factor depends on the type of radiation.
The effective radiation dose for an individual can be determined. To get it you can multiply the equivalent dose in each organ by a tissue-weight factor. This weighting factor depends on the part of the body that is exposed to radiation.
The absorbed dose is measured in gray (Gy). It represents the energy transmitted by radiation to living tissue. One gray corresponds to the energy of 1 joule (J) transmitted to 1 kilogram (kg) of living tissue.
Health effects on humans
In some reference countries, professionally exposed people cannot exceed 20 mSv (millisievert) per year.
¿What is acute radiation syndrome (ARS)? It is a collection of health effects. They are due to high radiation exposure that one receives from ionizing radiation over a short period of time. It is also known as radiation sickness or radiation poisoning.
On average, an American person receives a radiation dose of about 0.62 rem (620 millirem) each year.
For occupational exposure. In those cases the limit is 50 mSv in a single year. In a consecutive five-year period the maximum is of 100 mSv.
For the public to an average of 1 mSv (0.001 Sv) of effective dose per year. It doesn't include medical.
Sieverts received in Fukushima accident
During the Fukushima nuclear accident the technicians were exposed to 400 millisieverts per hour.
Continuous exposure to 400 mSv / h leads to a drop in white blood cells after a few hours. This drop-in white blood cells causes vomiting and headaches.
Sieverts received in the Chernobyl accident
In the Chernobyl nuclear accident, a large amount of radiation was released in a short time. The emergency workers and technicians on-site at the time could also process large doses of radiation.
Hundreds of thousands of people who were summoned to fight the disaster. These people were at increased risk. Later cases of leukemia appeared.
Other equivalent units
The sievert is the most widely used unit. It is used in the international system of units. However, there are many other equivalent and close units:
- Becquerel, Rutherford, and Curie. Nuclear source activity measurement units.
- Coulomb per kilogram, the röntgen or roentgen. Units of measurement of the gross energy flow of ionizing radiation.
- The gray, the obsolete rad unit, the Mache unit. Units of measurement of the total energy of ionizing radiation received (absorbed or not). The highest level of purely natural radiation ever recorded on the Earth's was on a Brazilian black beach. It was about 90 µGy/h.
- The rem, the sun unit or strontium unit, the volt per meter. One sievert equals 100 rem. The rem is an old unit of measurement, not recognized in the SI of measurements.
Dose examples in sieverts
- 98 nSv. Banana equivalent dose.
- 5–10 μSv. One set of dental radiographs.
- 80 μSv. Average dose to people living within 10 mi (16 km) of the plant during the Three Mile Island accident.
- 68 mSv. Estimated maximum dose to evacuees who lived closest to the Fukushima I nuclear accidents.
- 160 mSv. Chronic dose to lungs over one year smoking 1.5 packs of cigarettes per day, mostly due to inhalation of Polonium-210 and Lead-210.
- 670 mSv. The highest dose received by a worker responding to the Fukushima emergency.