The sievert is a unit in the International System of Units (SI) intended to represent the stochastic health risk of ionizing radiation, which is defined as the probability of causing radiation-induced cancer and genetic damage. The sievert is important in dosimetry and radiation protection. It is named after Rolf Maximilian Sievert, a Swedish medical physicist renowned for work on radiation dose measurement and research into the biological effects of radiation.
Radiation dosimetry in the fields of health physics and radiation protection is the measurement, calculation and assessment of the ionizing radiation dose absorbed by an object, usually the human body. This applies both internally, due to ingested or inhaled radioactive substances, or externally due to irradiation by sources of radiation.
Radiation protection, also known as radiological protection, is defined by the International Atomic Energy Agency (IAEA) as "The protection of people from harmful effects of exposure to ionizing radiation, and the means for achieving this". Exposure can be from a source of radiation external to the human body or due to internal irradiation caused by the ingestion of radioactive contamination.
A nuclear and radiation accident is defined by the International Atomic Energy Agency (IAEA) as "an event that has led to significant consequences to people, the environment or the facility. Examples include lethal effects to individuals, large radioactivity release to the environment, reactor core melt." The prime example of a "major nuclear accident" is one in which a reactor core is damaged and significant amounts of radioactive isotopes are released, such as in the Chernobyl disaster in 1986 and Fukushima nuclear disaster in 2011.
Equivalent dose is a dose quantity H representing the stochastic health effects of low levels of ionizing radiation on the human body which represents the probability of radiation-induced cancer and genetic damage. It is derived from the physical quantity absorbed dose, but also takes into account the biological effectiveness of the radiation, which is dependent on the radiation type and energy. In the SI system of units, the unit of measure is the sievert (Sv).
Radioactive contamination, also called radiological pollution, is the deposition of, or presence of radioactive substances on surfaces or within solids, liquids, or gases, where their presence is unintended or undesirable.
John William Gofman was an American scientist and advocate. He was Professor Emeritus of Molecular and Cell Biology at the University of California at Berkeley.
Chernobyl is the name of a Ukrainian city, the location of the 1986 Chernobyl nuclear disaster.
The Chernobyl disaster began on 26 April 1986 with the explosion of the No. 4 reactor of the Chernobyl Nuclear Power Plant, near the city of Pripyat in the north of the Ukrainian SSR, close to the border with the Byelorussian SSR, in the Soviet Union. It is one of only two nuclear energy accidents rated at seven—the maximum severity—on the International Nuclear Event Scale, the other being the 2011 Fukushima nuclear accident in Japan. The initial emergency response and subsequent mitigation efforts involved more than 500,000 personnel and cost an estimated 18 billion roubles—roughly US$68 billion in 2019, adjusted for inflation. It is considered the worst nuclear disaster in history.
A hot particle is a microscopic piece of radioactive material that can become lodged in living tissue and deliver a concentrated dose of radiation to a small area. A generally accepted theory proposes that hot particles within the body are vastly more dangerous than external emitters delivering the same dose of radiation in a diffused manner. Other researchers claim that there is little or no difference in risk between internal and external emitters, maintaining that individuals will likely continue to accumulate radiation dose from internal sources even after being removed from the original hazard and properly decontaminated, regardless of the relative danger from an internally sourced radiation dose compared to an equivalent externally sourced radiation dose.
Radiophobia is a fear of ionizing radiation. Examples include health patients refusing X-rays because they believe the radiation will kill them, such as Steve Jobs and Bob Marley who both died after refusing radiation treatment for their cancer. Given that overdoses of radiation are harmful, even deadly it is reasonable to fear high doses of radiation. The term is also used to describe the opposition to the use of nuclear technology arising from concerns disproportionately greater than actual risks would merit.
The 1986 Chernobyl disaster triggered the release of radioactive contamination into the atmosphere in the form of both particulate and gaseous radioisotopes. As of 2022, it was the world's largest known release of radioactivity into the environment.
Radiobiology is a field of clinical and basic medical sciences that involves the study of the effects of ionizing radiation on living things, in particular health effects of radiation. Ionizing radiation is generally harmful and potentially lethal to living things but can have health benefits in radiation therapy for the treatment of cancer and thyrotoxicosis. Its most common impact is the induction of cancer with a latent period of years or decades after exposure. High doses can cause visually dramatic radiation burns, and/or rapid fatality through acute radiation syndrome. Controlled doses are used for medical imaging and radiotherapy.
The roentgen or röntgen is a legacy unit of measurement for the exposure of X-rays and gamma rays, and is defined as the electric charge freed by such radiation in a specified volume of air divided by the mass of that air . In 1928, it was adopted as the first international measurement quantity for ionizing radiation to be defined for radiation protection, as it was then the most easily replicated method of measuring air ionization by using ion chambers. It is named after the German physicist Wilhelm Röntgen, who discovered X-rays and was awarded the first Nobel Prize in Physics for the discovery.
The Chernobyl disaster, considered the worst nuclear disaster in history, occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in the Ukrainian Soviet Socialist Republic, then part of the Soviet Union, now in Ukraine. From 1986 onward, the total death toll of the disaster has lacked consensus; as peer-reviewed medical journal The Lancet and other sources have noted, it remains contested. There is consensus that a total of approximately 30 people died from immediate blast trauma and acute radiation syndrome (ARS) in the seconds to months after the disaster, respectively, with 60 in total in the decades since, inclusive of later radiation induced cancer. However, there is considerable debate concerning the accurate number of projected deaths that have yet to occur due to the disaster's long-term health effects; long-term death estimates range from up to 4,000 for the most exposed people of Ukraine, Belarus, and Russia, to 16,000 cases in total for all those exposed on the entire continent of Europe, with figures as high as 60,000 when including the relatively minor effects around the globe. Such numbers are based on the heavily contested linear no-threshold model.
The committed dose in radiological protection is a measure of the stochastic health risk due to an intake of radioactive material into the human body. Stochastic in this context is defined as the probability of cancer induction and genetic damage, due to low levels of radiation. The SI unit of measure is the sievert.
Madan M. Rehani is an Indian-born medical physicist.
Ian Fairlie is a U.K. based Canadian consultant on radiation in the environment and former member of the three person secretariat to Britain’s Committee Examining the Radiation Risks of Internal Emitters (CERRIE). He is a radiation biologist who has focused on the radiological hazards of nuclear fuel and he has studied radioactive releases at nuclear facilities since before the Chernobyl accident in 1986.
This article uses Chernobyl as a case study of nuclear fallout effects on an ecosystem.
