Sievert, Unit To Measure The Radiation Dose Received
Sievert is a unit derived from the dose of ionizing radiation in the International System of Units. It is represented by the symbol Sv. It is a measure of the effect that low levels of ionizing radiation on the human body have on health. Sievert is of fundamental importance in dosimetry and radiation protection.
The quantities measured in sieverts are intended to represent the stochastic health risk, which for the evaluation of radiation dose is defined as the probability of induction of a cancer. of producing some genetic damage. A sievert carries a 5.5% probability of developing cancer eventually based on the linear model without threshold.
The name of sievert is due to the Swedish medical physicist Rolf Maximilian Sievert for his work in measuring the radiation dose in the investigation of the biological effects of radiation.
Sievert and the equivalent dose
Equivalent dose is a measure of the radiation dose received by tissue that is expressed in sievert. It has been attempted to correct the different biological effects of different types of ionizing radiation. The equivalent dose is, therefore, a less fundamental amount than the absorbed dose, but it is biologically more relevant.
The equivalent dose for a tissue is found by multiplying the absorbed dose by a radiation weighting factor, which depends on the type of radiation.
The effective radiation dose for an individual can then be determined by multiplying the equivalent dose in each organ by a tissue weighting factor. This weighting factor depends on the part of the body that is exposed to the radiation by adding the results of all the organs.
Effects of radioactivity on people
In some reference countries, professionally exposed persons cannot exceed 20 mSv (millisievert) per year.
Sieverts received in the two worst nuclear accidents in history: Fukushima and Chernobyl
During the Fukushima nuclear accident in Japan in March 2011, according to some reports, the plant technicians were exposed to 400 millisievert per hour. These values are within the dose limits described in Belgian legislation during rescue interventions in case of nuclear emergencies. A continuous exposure of 400 mSv /h h leads to a decrease in white blood cells after a few hours. This decrease in white blood cells causes vomiting and headaches.
In the Chernobyl nuclear accident in 1986, a large amount of radiation was released in a short time. Workers and emergency technicians who were in place at that time could also process large doses of radiation. After the Chernobyl nuclear disaster, much experience was gained about the influence of these irradiations on the human body.
The latest study by the United Nations organization UNSCEAR concludes that 134 emergency workers suffered from ionizing radiation diseases. Of these, 28 people died as a result of radiation. The 106 survivors suffered skin damage, cataracts due to radiation received. In addition, hundreds of thousands of people who were summoned to fight the disaster suffered a greater risk from radioactive exposure. Subsequently, cases of leukemia appeared.
Units equivalent and close to sievert to measure radiation
Although Sievert is a unit commonly used to talk about radiation there are many other equivalent and nearby units:
- Units of measurement of nuclear source activity: the becquerel, the Rutherford and the curie.
- Units of measurement of the gross energy flow of an ionizing radiation: the coulomb per kilogram, the röntgen or roentgen.
- Units of measurement of the total energy of ionizing radiation received (absorbed or not): the gray, the obsolete rad unit, the Mache unit.
- Units of measurement of radiation doses absorbed by living systems. Here is the well-known Sievert. Generally this unit is expressed in mSv / h.
- Other units of measurement of radioactivity: the rem, the sun unit or strontium unit, the volt per meter. A sievert equals 100 rem. The rem is an old unit of measurement, not recognized in the international measurement system.
Last review: January 29, 2020