Russia – Ukraine conflict : Chernobyl Exclusion Zone – one of the most radioactive places in the world

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The exclusion zone was established after the Chernobyl disaster, which happened on 04/26/1986 and became the largest disaster in human history.

There are Three controlled territories were defined on the territory:

  • A special zone (directly the Chernobyl territory);
  • 10 km zone;
  • 30 km zone.

The population was evacuated from the contaminated territories. For workers who left to service the power plant and the Exclusion Zone was organized dosimetric control of transport, and deployed decontamination points. At the borders of the zones was organized a transfer of workers from one vehicle to another to reduce the transfer of radioactive substances and radiation dust.

Unfortunately a huge zone left polluted outside the 30-kilometer zone, since the 1990s was made a gradual resettlement made of people from Polessky district, in which the level of contamination with radionuclides exceeded the established standards . Polesskoye, town. Vilcha, p. Dibrova, s. New World and many others was completely resettled till 1996. Since 1997, this territory became part of the Chernobyl zone, was transferred to the State Emergencies Ministry and included to the security perimeter.

As a result about 5 million hectares of land were removed from agricultural circulation, hundreds of small settlements were destroyed and buried (buried by heavy machinery), as well as personal cars and motor vehicles of evacuated residents, which also became infected and people were not allowed to leave on it. As a result of the accident has been decided to abandon the operation of the radar station Duga No. 1, which should become one of the main elements of the USSR missile defense.

Over 200 thousand km² has been polluted. Radioactive substances spread in the aerosols, which gradually settling on the surface of the earth. Noble gases scattered in the atmosphere and did not pollution the regions adjacent to the station. The pollution was very uneven, it depended on the direction of the wind in the first days after the accident. The most affected areas are in the immediate vicinity of the Chernobyl nuclear power plant: the northern regions of the Kiev and Zhytomyr regions of Ukraine, the Gomel region of Belarus and the Bryansk region of Russia.

In cities, the majority of hazardous substances accumulated on flat surface areas: on lawns, roads, roofs. Under the influence of wind and rains, the degree of pollution has greatly decreased, and now the radiation levels in most places have returned to previous values. In agricultural areas, during first months, radioactive substances deposited on the leaves of plants and on the grass, so herbivores were infected.

Forests have been heavily polluted. Due to the fact that cesium is constantly recycled in the forest ecosystem without removing, the levels of contamination of forest goods, such as mushrooms, berries and game, remain dangerous. Over the next decades the level of pollution of rivers and most lakes is currently low, but in some “closed” lakes, of which there is no runoff, the concentration of cesium in water and fish can be dangerous.

Pollution was not limited to a 30-kilometer zone. An increased content of cesium-137 was noted in lichen and deer meat in the Arctic regions of Russia, Norway, Finland and Sweden.

The Chernobyl Exclusion Zone is one of the most radioactive places in the world. On April 26, 1986, a disastrous meltdown at the Chernobyl nuclear power plant in Ukraine (in the former USSR) led to two enormous explosions that blew the 2,000-ton (1,800 metric tons) lid (opens in new tab)off one of the plant’s reactors, blanketing the region with reactor debris and its radioactive fuel. The explosion released into the atmosphere 400 times more radiation than was produced by the atomic bomb dropped on Hiroshima, and nuclear fallout rained down far and wide across Europe, according to a report by the European Parliament(opens in new tab)

On May 2, 1986, a Soviet Union commission officially declared an off-limits area around the disaster and called it the Chernobyl Exclusion Zone. The zone includes an area of roughly 1,040 square miles (2,700 square kilometer) around the 18.6 mile (30 km) radius of the plant; the area was considered the most severely irradiated environment and was cordoned off to anyone but government officials and scientists, according to the U.S. Department of Energy(opens in new tab).

By April 27 (the day after the explosion), officials had already evacuated the nearby city of Pripyat, but fresh orders in May were given to evacuate everyone who remained within the exclusion zone. Over the following weeks and months, around 116,000 people would be relocated from inside the exclusion zone. This number continued to grow, reaching a total of around 200,000 people before the end of the evacuation, according to the International Atomic Energy Agency(opens in new tab).

According to the U.S. Department of Energy, during the first year of its existence, the 18.6 mile (30 km) mile exclusion zone was further split into three distinct regions:

— The inner exclusion zone: the high-radiation region within a 6.2 mile (10 km) radius of the plant from which the population was to be evacuated and permanently forbidden reentry.

— The zone of temporary evacuation: a moderately irradiated region to which the public could return once the radiation had decayed to safe levels.

— The zone of rigorous monitoring: a sporadically irradiated region from which children and pregnant women were moved into less irradiated areas in the immediate aftermath of the disaster.

The exclusion zone has expanded in subsequent years. When the Ukranian exclusion zone is added together with the neighboring Belarusian exclusion zone, the combined area makes up an approximate 1,550 square miles (4,000 square kilometers), according to the European Radioecology Exchange Alliance.

At the beginning of 2022, increasing tensions between Russia and NATO over Ukraine’s potential membership to the western military alliance has also led to an increased guard presence inside the Chernobyl Exclusion Zone, according to Sky News(opens in new tab). The region, which lies close to Ukraine’s northern border with Russia’s ally Belarus and straddles the most direct route between it and Ukraine’s capital, Kiev, was stationed with 7,500 more border guards between December 2021 and February 2022.

More than 100 radioactive elements were released into the atmosphere immediately after the disaster, according to the International Atomic Energy Agency(opens in new tab) (IAEA). The most dangerous of them were isotopes of iodinestrontium and cesium, which have respective radioactive half-lives (the period of time it takes for half of the material to decay) of 8 days, 29 years and 30 years. The majority of the elements released were short-lived (meaning their half-lives are no more than a few weeks or even days), but the long half-lives of strontium and cesium mean they are still present in the area. At low levels, iodine can cause thyroid cancer; strontium leukemia; and cesium has especially damaging effects on the liver and spleen, according to the IAEA.

Still other radioactive elements released in the explosion are much longer lived, such as plutonium-239 which has a half-life of 24,000 years. And so despite the entire Chernobyl Exclusion Zone being much less radioactive today than it was in the days immediately following the disaster, the longest-lived radioactive materials inside the zone could still take thousands of years for half of their atomic nuclei to decay, according to the National Geographic(opens in new tab). Radiation readings taken within the zone show that its more contaminated areas still contain dangerous amounts of radiation.

Map of surface ground deposition of caesium due to the Chernobyl accident

As the contamination was invisible, the release of radionuclides into the surrounding environment showed little hint of disaster. However, when released into the atmosphere, each radioactive particle has a probability of forcing changes in both DNA and the immune system, changes that in turn can decrease an individual’s ability to cope with even low levels of radiation.

Radioactive fall-out from the atmosphere is stored within soils, from here transferring into vegetation and upwards through the food chain, and ultimately increasing the likelihood of cancer. In the case of environmental chemical pollution, risk of serious diseases may increase significantly. As detailed below, ArcGIS and the Geostatistical Analyst extension were used to perform detailed analysis of radiation contamination and its links to health.

Before the 20th Century, concentrated radionuclides were mostly confined within the earths crust and remained harmless to humans. Technological development has resulted in the dispersal of such elements at a greatly accelerated rate. The ground nuclear weapon tests in the middle of the twentieth century released plutonium into the wider environment.

Prior to the tests, plutonium was concentrated in uranium and thorium ores at the estimated levels of 10-9 – 10-7 Bequerel/gram, with each Bequerel representing one radioactive decay per second. In Belarus, the tests resulted in the increase of plutonium concentration levels in upper soil layers to 10-5 – 10-4 Bq/g. After the Chernobyl accident, the concentration of plutonium in upper soil layers in southern Belarus increased to alarming values of 0.1 – 0.2 Bequerel/gram.

Nowadays internal exposure from intake of food contaminated by radiocesium contributes to more than half of the whole radiation dose received by Byelorussian people. Income of the inhabitants of villages in southern Belarus does not afford them access to non-contaminated food. They consume vegetables, potatoes, and milk produced on their own contaminated personal properties as well as mushrooms and berries from nearby forests.

After intake, cesium is quickly absorbed and distributed almost uniformly in the human body. It is removed from the body through kidneys. Assuming that people are eating locally grown food and that cesium intake is constant throughout the year, approximate cesium absorption can be estimated as the following. If the daily cesium intake is q0, the accumulated amount of cesium in the body on subsequent days is the following:

Here λe is the effective speed of elimination of the radionuclide from the body due to biology and radioactive decay. For adults λe ≈ 0.0063 1/day. Summing up the geometric progression, we can estimate the amount of cesium in the body in n days as:

Cesium accumulation in the human body at 1 constant intake eventually slows down due to the exponential nature of the radioactive decay, as well as due to the elimination of the radionuclide from the body by metabolism. Accumulation of cesium in a human body through the contaminated food in rural Belarus in 1993 is displayed in figure 3.

Figure 3. Accumulation of cesium through contaminated food in rural Belarus in 1993, in milliSieverts.

According to the legislation, the maximum radiation dose in unrestricted areas shall be such that an individual would not receive a dose in excess of one milliSievert to the whole body per year.

In southern Belarus, a person can receive a one milliSievert dose during the summer only by eating regular food. If this person leaves this territory and moves to a non- contaminated place, three months later there will still be a half of the dose in his or her body.

The radionuclide deposition maps below were created in 1999 with a prediction for the year 2000. 

Radiation exposure and contamination

Types of radiation

Radiation includes

  • High energy electromagnetic waves (X-rays, gamma rays)
  • Particles (alpha particles, beta particles, neutrons)

Alpha particles are energy nuclei of helium emitted by some high atomic number radionuclides (eg, plutonium, radium, uranium); they cannot penetrate through the skin beyond minimum thicknesses ( < 0.1 mm).

Beta particles are high-energy electrons emitted from the nuclei of unstable atoms (eg, cesium-137, iodine-131). These particles can penetrate deeper into the skin (1-2 cm) and cause damage to both epithelial and subepithelial tissue.

Neutrons are electrically neutral particles emitted by some radionuclides (eg, californium-252) and produced in nuclear fission reactions (eg, in nuclear reactors); their depth of penetration can vary from a few millimeters to several tens of centimeters, depending on their energy. They collide with the nuclei of stable atoms, causing the emission of energetic protons, alpha and beta particles, and gamma radiation.

Gamma and X rays are electromagnetic radiation (i.e., photons) of very short wavelength that can penetrate deep into tissues (several centimeters). While some photons deposit all their energy in the body, other photons of the same energy can deposit only a fraction of their energy, and others can pass completely through the body without interacting.

Because of these characteristics, alpha and beta particles cause the greatest damage when the radioactive atoms that emit them are inside the body (internal contamination) or, in the case of beta-emitters, directly on the body; only the tissue in close proximity to the radionuclide is affected. Gamma and X-rays can cause injury away from their source and are typically responsible for acute radiation syndromes. 

Acute radiation syndromes can be caused by a sufficient dose of some internally deposited radionuclides which are widely distributed in tissues and organs and have a high specific activity. For example, polonium 210 (Po-210) has a specific activity of 166 terabecquerel per gm (TBq / g) and 1 mcg (size of a grain of salt) of Po-210 delivers a whole body dose of 50 Sv (~ 20 times the median lethal dose).

Measurement of radiation

The conventional units of measurement are the roentgen, the rad and the rem. The roentgen (R) is a unit of exposure measurement that measures the ionizing capacity of X or gamma rays in air. The absorbed radiation dose (rad) is the amount of radiation energy absorbed per unit of mass. 

Since biological damage per rad varies with the type of radiation (eg, it is higher for neutrons than for X or gamma rays), the dose expressed in rad is corrected with a quality factor; the resulting equivalent dose unit is the human roentgen equivalent (rem). Outside the United States and in the scientific literature, International System (SI) units are used, in which rad is replaced by gray (Gy) and rem by sievert (Sv);100 rem. The rad and the rem (and therefore the Gy and the Sv) are substantially the same (that is, the quality factor is equal to 1) when describing X or gamma or beta rays.

The amount of radioactivity is expressed in terms of the number of nuclear disintegrations (transformations) per second. The becquerel (Bq) is the SI unit of measure for radioactivity; one Bq equals 1 disintegration per second (dps). In conventional units sometimes still used in the United States, one curie corresponds to 37 billion Bq.

Types of exposure

Radiation exposure can result from

  • Contamination
  • Irradiation

Radioactive contamination is caused by accidental contact and retention of radioactive material, usually in the form of powder or liquid. Contamination can be

  • External
  • Internal

External contamination occurs on the skin or clothing, from which it can partly fall or be brushed off, contaminating other objects and people. Internal contamination results from radioactive materials within the body, which can accidentally enter by ingestion, inhalation, or through skin lesions. Once in the body, radioactive material can be transported to various sites (eg, in the bone marrow), where it continues to emit radiation until it is removed or decays. Internal contamination is more difficult to remove. Although internal contamination is possible with any radionuclide, historically, the majority of cases where contamination has resulted in a significant risk to the patient has been caused by a relatively small number of radionuclides,

Irradiation is exposure to radiation, but not to radioactive material (ie, no contamination is present). Radiation exposure can occur without the radiation source (eg, radioactive material, or X-ray device) being in contact with the person. When the radiation source is removed or turned off, the exposure ends. Irradiation can affect the whole body, and this, if the dose is high enough, can cause systemic symptoms and radiation syndromes ; or it can affect a small part of the body (eg, following radiation therapy), and this can induce local effects. Following irradiation, exposed individuals do not emit radiation (ie, they do not become radioactive).

Sources of exposure

Sources can be natural or man-made (see United States Average Annual Radiation Exposure table ).

The population is constantly exposed to low levels of natural radiation called background radiation. Background radiation comes from cosmic rays and radioactive elements in water, air and soil. Cosmic radiation is concentrated at the poles by the Earth’s magnetic field and attenuated by the atmosphere.

Therefore, the exposure is greater in subjects living in high latitudes, at high altitudes, or in both conditions; exposure also increases during air travel. Earth’s sources of external radiation exposure are mainly due to the presence of radioactive elements with half-lives comparable to the age of the earth (~ 4.5 billion years).

In particular, uranium-238 and thorio-232 are present in many rocks and minerals together with several dozen radioactive products of their decay, and a radioactive isotope of potassium (K-40). Small amounts of these radionuclides are found in food, water and air, and therefore contribute to internal exposure as they are inevitably incorporated into the body. Most of the dose resulting from internally incorporated radionuclides comes from carbon (C-14) and potassium (K-40) radioisotopes, and as these and other elements (stable and radioactive forms) are constantly ingested into the body by ingestion and inhalation, there are about 7000 atoms subject to radioactive decay every second.

Internal exposure caused by inhalation of radioactive isotopes of the noble gas radon (Rn-222 and Rn-220), which are also formed by the decay series of uranium 238, represents the major portion (73%) of the dose per capita average of radiation from natural sources in the US population. Cosmic radiation is responsible for 11%, radioactive elements in the body for 9%, and external terrestrial radiation for 7%. 

In the United States, the population receives an average effective dose of approximately 3 millisieverts (mSv) / year from natural sources (ranging from ~ 0.5 to 20 mSv / year). However, in some parts of the world,> 50 mSv / year is received. Doses from natural background radiation are far too low to cause radiation injury;

In the United States, about 3 mSv / year are received on average from man-made sources, most of which are diagnostic imaging equipment. Considering the per capita dose, the contribution of diagnostic exposure is higher following CT and nuclear cardiology procedures. 

However, medical diagnostic procedures rarely impart sufficient doses to cause radiation injury, although there is a small theoretical increase in cancer risk. Exceptions include some prolonged interventional procedures conducted under fluoroscopic guidance (eg, endovascular reconstruction, vascular embolization, cardiac or tumor ablation with radiofrequency); these procedures resulted in lesions of the skin and underlying tissues.

A fraction of the average exposure for the general population arises from accidents and radioactive fallout from nuclear weapons testing. Accidents may involve industrial irradiation or X-ray equipment and nuclear reactors. Such incidents typically occur due to failure to follow safety procedures (eg, when interlocks are bypassed). The loss or theft of industrial or medical sources containing large amounts of radionuclides has also resulted in radiation injuries. People seeking medical treatment for such injuries may not be aware that they have been exposed to radiation.

There have been unintended releases of radioactive materials, including that at the Three Mile Island power plant in Pennsylvania in 1979, the Chernobyl reactor in Ukraine in 1986, and the Fukushima Daiichi nuclear power plant in Japan in 2011. The exposure thereafter. the Three Mile Island accident was minimal because there was no rupture of the containment structure as it did in Chernobyl, nor hydrogen explosions as occurred in Fukushima. People living within one mile of Three Mile Island received only about 0.08 mSv at most (a fraction of the dose one is exposed to in a month from natural sources). 

In reverse, the 115,000 people who were eventually evacuated from the area around the Chernobyl power plant received an average effective dose of about 30 mSv and an average thyroid dose of about 490 mGy. People who worked at the Chernobyl power plant at the time of the accident received significantly higher doses. 

More than 30 of the workers and emergency response personnel died within months of the accident, and many more suffered from acute radiation syndrome. Low levels of contamination resulting from this incident were found as far as Europe and Asia, and even (to a lesser extent) North America. It has been estimated that the average cumulative exposure for the general population in various affected regions of Belarus, Russia and Ukraine over a period of 20 years since

The earthquake and tsunami in Japan in 2011 led to the release of radioactive material from several reactors at the Fukushima Daiichi nuclear power plant into the environment. There were no serious radiation-induced injuries among on-site workers. In the nearly 400,000 residents of Fukushima prefecture, the estimated effective dose (based on interviews and dose reconstruction models) was <2 mSv for 95% of the population and <5 mSv for 99.8%. 

WHO estimates were somewhat higher due to deliberately more conservative exposure assumptions. The effective dose in prefectures not immediately adjacent to Fukushima was estimated to be between 0.1 and 1 mSv, and the dose in populations outside of Japan was negligible (<0.01 mSv).

The most significant radiation exposure for a population occurred following the detonation of two atomic bombs on Japan in August 1945, which caused approximately 110,000 deaths from the immediate trauma of the blast and heat. Far fewer (<1000) additional deaths from radiation-induced cancer occurred over the next 70 years. Continuous health surveillance of survivors remains among the most important sources for estimating radiation-induced cancer risk.

Although several criminal cases of intentional contamination of individuals have been reported, radiation exposure of a population as a result of terrorist activities has never occurred but remains a concern. One possible scenario involves using a device to contaminate an area by dispersing radioactive material (eg, from a disused industrial source of cesium-137 or cobalt-60 for radiotherapy). A radiation scattering device that uses conventional explosives is called a dirty bomb. Other terrorist scenarios include using a hidden source of radiation to expose unsuspecting people to large doses of radiation, attacking a nuclear reactor or radioactive material depot, and detonating a nuclear weapon (eg, an improvised nuclear device, a stolen weapon).

Pathophysiology of exposure and radiation contamination

Ionizing radiation can damage DNA, RNA and proteins directly, but damage to these molecules is usually indirect, caused by the highly reactive free radicals generated by the interaction of the radiation with intracellular water molecules. High doses of radiation can cause cell death, and smaller doses can interfere with endogenous systems of molecular repair, homeostasis, and cell proliferation. Damage to these and other cellular components can lead to progressive hypoplasia, atrophy and ultimately tissue fibrosis. 

However, it is now clear that cell killing alone cannot explain many tissue reactions, because such reactions also depend on complex events including inflammatory, chronic oxidative and immune reactions. as well as damage to the vascular system and the extracellular matrix. In general, early reactions, such as in the skin and gastrointestinal tract, involve killing the early stem / progenitor cells that supply mature functional cells in the tissue, as well as inflammatory reactions. 

On the other hand, late reactions (eg, in the lung, kidney, and brain) involve complex and dynamic interactions between multiple cell types in tissues and organs and include immune cell infiltration, cytokine production, and factors of growth, often in cyclical and persistent cascades, and chronic oxidative stress. killing of early stem / progenitor cells that supply mature functional cells in the tissue, as well as inflammatory reactions.

 On the other hand, late reactions (eg, in the lung, kidney, and brain) involve complex and dynamic interactions between multiple cell types in tissues and organs and include immune cell infiltration, cytokine production, and factors of growth, often in cyclical and persistent cascades, and chronic oxidative stress. killing of early stem / progenitor cells that supply mature functional cells in the tissue, as well as inflammatory reactions. 

On the other hand, late reactions (eg, in the lung, kidney, and brain) involve complex and dynamic interactions between multiple cell types in tissues and organs and include immune cell infiltration, cytokine production, and factors of growth, often in cyclical and persistent cascades, and chronic oxidative stress.

Factors influencing the response

The biological response to radiation varies with

  • Radiosensitivity of the tissue
  • Dose
  • Dosage
  • Duration of exposure
  • Degree of inflammatory response
  • Age of the patient
  • Comorbidità
  • Presence of DNA repair genetic defect disorders (eg, ataxia-telangiectasia , Bloom syndrome, Fanconi anemia)

Cells and tissues differ in radiosensitivity. In general, undifferentiated cells and those that have high mitotic rates (eg, stem cells, cancer cells) are particularly vulnerable to radiation. Since radiation preferentially eliminates rapidly dividing stem cells over more resistant mature cells, there is usually a latency period between radiation exposure and the manifestation of radiation damage. The lesions do not manifest until a significant fraction of mature cells have died of natural senescence and, due to the loss of stem cells, are not replaced.

The approximate cell sensitivity in descending order from the most sensitive to the least sensitive cell type is

  • Lymphoid cells
  • Germ cells
  • Bone marrow proliferating cells
  • Intestinal epithelial cells
  • Epidermal stem cells
  • Liver cells
  • Epithelium of the pulmonary alveoli and bile ducts
  • Renal epithelial cells
  • Endothelial cells (pleura and peritoneum)
  • Connective tissue cells
  • Cells of the bone tissue
  • Muscle, brain and spinal cord cells

The severity of the radiation damage depends on the dose and the length of time over which that dose is spread. A high, single rapid dose is more harmful than the same dose given over the course of weeks or months. The effect of a given dose also depends on the exposed body fraction. Following a whole body dose of > 4.5 Gy administered over a short period of time, significant injury is certain to occur and death is possible (minutes to hours); however, doses of tens of Gy can be well tolerated if delivered over a long period of time to a limited surface area of ​​tissue (eg, in the treatment of cancer).

Other factors can increase sensitivity to radiation damage. Children are more sensitive to radiation damage as they have a higher rate of cell proliferation. Individuals homozygous for the ataxia telangiectasia gene show considerably greater sensitivity to radiation damage. Some disorders, such as connective tissue disorders and diabetes, can increase sensitivity to radiation damage. 

Some drugs and chemotherapeutic agents (eg, actinomycin D, doxorubicin, bleomycin, 5-fluorouracil, and methotrexate) can also increase sensitivity to radiation damage. Some chemotherapeutic agents (eg, doxorubicin, etoposide , paclitaxel , epirubicin), antibiotics (eg,cefotetan ), statins (eg, simvastatin), and herbal preparations can produce an inflammatory skin reaction at the site of previous irradiation (radiation booster) weeks to years after exposure to the same location.

Carcinogenic, teratogenic and heritable effects

Radiation-induced genetic damage to somatic cells can cause malignant transformation, while in utero exposure can lead to teratogenic effects and damage to germ cells increases the theoretical possibility of genetically transmissible defects.

Continued exposure to 0.5 Gy throughout the body is estimated to increase the lifetime risk of cancer death for an average adult from approximately 22% to approximately 24.5%, an increased relative risk of ‘11%, but only 2.5% as regards the absolute risk. The risk of cancer from commonly encountered doses (i.e., those resulting from background radiation and typical diagnostic procedures Risks arising from medical radiation) is much less and could be null. 

Estimates of the increased risk of radiation-induced cancer due to the typically low doses received by people in the vicinity of nuclear reactor accidents such as Fukushima were made by extrapolating the effects for low doses from the known effects of much higher doses. 

The resulting very small theoretical effect is multiplied by a large population producing what may appear to be an alarming number of additional cancer deaths. The validity of these extrapolations cannot be confirmed because the hypothesized increase in risk is too small to be detected by epidemiological studies, and the possibility that there is not an increased risk of cancer from these types of exposures cannot be excluded.

Children are more sensitive because they have more cell divisions ahead of them and a longer life span during which cancer can occur. A CT scan of the abdomen performed on a 1-year-old child is estimated to increase the child’s estimated absolute risk of developing cancer over a lifetime by approximately 0.1%. Radionuclides incorporated into specific tissues are potentially carcinogenic at such sites (eg, the Chenorbyl reactor accident caused a considerable increase in radioactive iodine intake due to consumption of contaminated milk, and among exposed infants it occurred an increase in the number of thyroid cancer cases).

The fetus is exceptionally susceptible to damage from radiation at high doses. However, at doses < 100 mGy, teratogenic effects are unlikely. The risk to the fetus of radiation damage at the doses typically used in diagnostic procedures that pregnant women are likely to undergo is very small compared to the overall risk of congenital defects (2% to 6% of observable cases at birth) and the potential diagnostic benefit of the test. The increased risk of cancer from exposure to radiation in utero is about the same as that resulting from radiation exposure in children, which is approximately 2 to 3 times the risk for an adult of 5. % / Sv.

The potential risks of radiation exposure necessitate careful consideration of the need for (or alternatives) imaging tests involving the use of radiation, optimization of radiation exposure for body habitus and clinical issue, and ” attention to the use of adequate radiation protection procedures, particularly in children and pregnant women.

Damage to reproductive cells has been shown to cause congenital abnormalities in the offspring of severely irradiated animals. However, no hereditary effects have been found in children born to people exposed to radiation, including children of atomic bomb survivors in Japan or children of cancer survivors treated with radiation therapy. The mean dose to the ovaries was ~ 0.5 Gy and to the testes 1.2 Gy.

Symptoms of exposure and radiation contamination

Clinical manifestations vary depending on whether the radiation exposure involves the whole body ( acute radiation syndrome ) or is limited to a small area ( focal radiation lesion ).

Acute radiation syndromes

After the whole body, or a large part of it, receives a high dose of penetrating radiation, several distinct syndromes can occur:

  • Cerebrovascular syndrome
  • Gastrointestinal syndrome
  • Hematopoietic syndrome

These syndromes have 3 different phases:

  • Prodromal phase (a few minutes to 2 days after exposure): lethargy and gastrointestinal symptoms (nausea, anorexia, vomiting, diarrhea) are possible.
  • Latent asymptomatic phase (a few hours to 21 days after exposure)
  • Phase of overt systemic disease (a few hours to> 60 days after exposure): the disease is classified according to the main organ system involved

The type of syndrome that develops, its severity and the speed of its progression depend on the radiation dose (see table Effects of whole-body irradiation from external radiation or internal absorption ). Symptoms and course are relatively constant for a given radiation dose and therefore can help estimate the level of exposure.

Cerebrovascular syndrome is the predominant manifestation following extremely high doses of radiation distributed throughout the body ( > 30 Gy) and is always fatal. The prodromal phase develops from a few minutes to 1 h after exposure. There is little or no latent phase. Patients develop tremors, epilepsy, ataxia, and brain edema, and die within hours to 1-2 days.

Gastrointestinal syndrome is the main manifestation following whole body doses of approximately 6-30 Gy. The often marked prodromal period develops within approximately 1 h and resolves within 2 days. During the 4-5 day latent period, the cells of the gastrointestinal mucosa die. Cell death is followed by intractable nausea, vomiting and diarrhea, leading to severe dehydration and electrolyte imbalances, decreased plasma volume and circulatory collapse. Intestinal necrosis can also arise, predisposing to intestinal perforation, bacteremia and sepsis. Death is common. Patients receiving >10 Gy may exhibit cerebrovascular symptoms (suggesting they have been exposed to a lethal dose). Survivors also develop hematopoietic syndrome.

The hematopoietic syndrome it is the dominant manifestation following whole body doses of approximately 1-6 Gy and consists of generalized pancytopenia. A mild prodromal manifestation may begin after 1-6 h and last for 24-48 h. Stem cells in the bone marrow shrink considerably, but the mature blood cells in circulation remain largely unaffected. Circulating lymphocytes are an exception, and lymphopenia can become evident within hours or days of exposure. 

When circulating cells die from senescence, they are not replaced in sufficient numbers, resulting in pancytopenia. Thus, patients remain asymptomatic for a latency period of up to 4.5 weeks after a 1 Gy dose, during which hematopoiesis blockade worsens. The risk of various infections increases due to the neutropenia (more important from 2 to 4 weeks) and decreased production of Ac. Petechiae and mucosal bleeding result from thrombocytopenia , which develops within 3 to 4 weeks and can persist for months. Anemia sets in slowly, because pre-existing red blood cells have a longer life than white blood cells and platelets. Survivors have an increased incidence of radiation-induced malignancies, including leukemia .

Symptoms of exposure and radiation contamination

Clinical manifestations vary depending on whether the radiation exposure involves the whole body ( acute radiation syndrome ) or is limited to a small area ( focal radiation lesion ).

Acute radiation syndromes

After the whole body, or a large part of it, receives a high dose of penetrating radiation, several distinct syndromes can occur:

  • Cerebrovascular syndrome
  • Gastrointestinal syndrome
  • Hematopoietic syndrome

These syndromes have 3 different phases:

  • Prodromal phase (a few minutes to 2 days after exposure): lethargy and gastrointestinal symptoms (nausea, anorexia, vomiting, diarrhea) are possible.
  • Latent asymptomatic phase (a few hours to 21 days after exposure)
  • Phase of overt systemic disease (a few hours to> 60 days after exposure): the disease is classified according to the main organ system involved

The type of syndrome that develops, its severity and the speed of its progression depend on the radiation dose (see table Effects of whole-body irradiation from external radiation or internal absorption ). Symptoms and course are relatively constant for a given radiation dose and therefore can help estimate the level of exposure.


Effects of irradiation on the whole body from external radiation or internal absorption

Stage of the syndromeCharacteristicDose interval (Gy) *, †
1–22-66-88-30> 30
Prodromal phaseIncidence of nausea and vomiting5-50%50-100%75-100%90-100%100%
Time to onset of nausea and vomiting after exposure ‡2-6 h1-2 h10-60 minutes< 10 minutesMinutes
Duration of nausea and vomiting< 24 h24-48 h< 48 h< 48 hN / A (patients die in < 48 h)
Severity and incidence of diarrheaAbsentNone to mild ( < 10%)Moderate to severe ( > 10%)Severe ( > 95%)Severe (100%)
Time of onset of diarrhea after exposure3-8 h1-3 h< 1 h< 1 h
Severity and incidence of headacheLightMild to moderate (50%)Moderate (80%)Severe (80-90%)Severe (100%)
Onset of headache after exposure4-24 h3-4 h1-2 h< 1 h
Severity of feverAfebrileModerate increaseModerate to severeSeriousSerious
Incidence of fever10-100%100%100%100%
Time of onset of fever after exposure1-3 h< 1 h< 1 h< 1 h
Central nervous system functionNo dysfunctionCognitive impairment for 6-20 hCognitive impairment for > 24 hAt higher doses, rapid loss of capacityYou may have a lucidity interval of a few hoursAtaxiaConvulsionsTremorLethargy
Latency periodNo symptoms28-31 days7-28 days< 7 daysAbsentAbsent
Overt diseaseClinical manifestationsMild to moderate leukopeniaTirednessAstheniaModerate to severe leukopeniaPurpleHemorrhageInfectionsHair loss beyond 3 GySevere leukopeniaHigh feverDiarrheaHe retchedVertigo and disorientationHypotensionElectrolyte imbalancesNauseaHe retchedSevere diarrheaHigh feverElectrolyte imbalancesShockN / A (patients die in < 48 h)
Main organ system syndromeHematopoieticHematopoieticGastrointestinal (mucosal cells)Gastrointestinal (mucosal cells)Central nervous system
RecoveryOutpatient observationRecommended to necessaryUrgentPalliative treatment (symptomatic only)Palliative treatment (symptomatic only)
Acute mortality without medical assistance0-5%5-100%95-100%100%100%
Acute mortality with medical assistance0-5%5-50%50-100%100%100%
Death6-8 weeks4-6 weeks2-4 weeks2 days-2 weeks1-2 days
* 1 rad = 1 cGy; 100 rad = 1 Gy.
† Whole body irradiation with doses up to 1 Gy is unlikely to cause any symptoms.
‡ Although the time between exposure and the onset of emesis is a quick and inexpensive method of estimating radiation dose, it should be used with caution as it is imprecise and produces a high rate of false positives. Additional information, such as lymphocyte counts and details on potential exposure, improve accuracy.
Adapted from Military Medical Operations Armed Forces Radiobiology Research Institute: Medical Management of Radiological Casualties , edition 2. April 2003.

Cerebrovascular syndrome is the predominant manifestation following extremely high doses of radiation distributed throughout the body ( > 30 Gy) and is always fatal. The prodromal phase develops from a few minutes to 1 h after exposure. There is little or no latent phase. Patients develop tremors, epilepsy, ataxia, and brain edema, and die within hours to 1-2 days.

Gastrointestinal syndrome is the main manifestation following whole body doses of approximately 6-30 Gy. The often marked prodromal period develops within approximately 1 h and resolves within 2 days. During the 4-5 day latent period, the cells of the gastrointestinal mucosa die. Cell death is followed by intractable nausea, vomiting and diarrhea, leading to severe dehydration and electrolyte imbalances, decreased plasma volume and circulatory collapse. Intestinal necrosis can also arise, predisposing to intestinal perforation, bacteremia and sepsis. Death is common. Patients receiving >10 Gy may exhibit cerebrovascular symptoms (suggesting they have been exposed to a lethal dose). Survivors also develop hematopoietic syndrome.

The hematopoietic syndrome it is the dominant manifestation following whole body doses of approximately 1-6 Gy and consists of generalized pancytopenia. A mild prodromal manifestation may begin after 1-6 h and last for 24-48 h. Stem cells in the bone marrow shrink considerably, but the mature blood cells in circulation remain largely unaffected. Circulating lymphocytes are an exception, and lymphopenia can become evident within hours or days of exposure. When circulating cells die from senescence, they are not replaced in sufficient numbers, resulting in pancytopenia. Thus, patients remain asymptomatic for a latency period of up to 4.5 weeks after a 1 Gy dose, during which hematopoiesis blockade worsens. The risk of various infections increases due to the neutropenia (more important from 2 to 4 weeks) and decreased production of Ac. Petechiae and mucosal bleeding result from thrombocytopenia , which develops within 3 to 4 weeks and can persist for months. Anemia sets in slowly, because pre-existing red blood cells have a longer life than white blood cells and platelets. Survivors have an increased incidence of radiation-induced malignancies, including leukemia .

The situation in Chernobyl in the Russia – Ukraine conflict

Ukrainian technicians who monitor what remains of the Chernobyl power plant after the 1986 disaster reported the surprising superficiality of the Russian soldiers who took over the area as early as February 24 without taking any precautions, especially for themselves.
In short, the leaders of Moscow would have sent them into trouble: without suitable clothing and, many of them, without training and NBC equipment (nuclear, biological and chemical).

The engineers and maintenance workers of the reactor and the thick reinforced concrete “coat” built above it would also have tried to warn Russian soldiers that they could not go back and forth from the plant premises to the surrounding area without undergoing decontamination processes. to dispose of the radioactive dust from clothes shoes, but there was nothing to be done.
During surveillance activities, the Russian military also dug trenches in the Red Forest, the most contaminated area in the world after the 1986 accident.
In short, they handled, without protection, with their bare hands, the “source of cobalt-60”.

Technicians at the plant reported that a Russian soldier from a chemical, biological and nuclear protection unit took a source of cobalt-60 from a nuclear waste repository with his bare hands, exposing himself to such radiation in seconds from make the Geiger counter splash.

The International Atomic Energy Agency (IAEA) said on Feb. 25 that radiation levels at the Chernobyl site reached 9.46 microsieverts per hour but remained “within an operating range” recorded in the exclusion zone from the moment of its creation and posed no threat to the general population.

The safe levels, by IAEA standards listed on the agency’s official website, are up to 1 millisievert per year for the general population and 20 millisievert per year for those who deal with radiation professionally – where 1 millisievert is equal to 1,000 microsieverts.

What is “Microsievert”?

Keywords; radiation, sievert, millisievert, microsievert

  • We see the word “microsievert” frequently on TV and newspapers. What is it?
  •   The “sievert” is the unit representing the amount of radiation. (* To be accurate, it represents the level of influence on human bodies when they absorb energy from radiation, but you may experience no inconvenience if you take it as amount of radiation.)
  • The “millisievert” is one-thousandths of a “sievert” and the “microsievert” is one-thousandths of a “millisievert.”

Keywords: daily life and radiation, natural radiation, radiation from natural foodstuffs, regional difference

  • The bigger the value is, the greater influence it exerts on human bodies.  Then, which value should we use as a guideline? In this case, it may be more understandable if we compare the values with a variety of values of radiation that exists in our daily life.
  • Let’s look at Fig. 1 (Daily Life and Radiation). You may see in the middle part on the left a description of “Natural radiation (annual) per person,” which shows worldwide, annual average radiation exposure of 2,400 microsieverts (2.4 millisieverts). This is the amount of radiation received from the natural world when we live an ordinary life.
  • The breakdown of sources indicated inside the balloon (on the left side of Fig. 1 shows as follows (Note that only the values inside the balloon are in millisieverts): 0.39 millisieverts (390 microsieverts) from the space and 0.48 millisieverts (480 microsieverts) from the earth. They are radiation received from outside the human body (* it is called “external exposure”). There are also other sources: 0.29 millisieverts (290 microsieverts) from foodstuffs and 1.26 millisieverts (1,260 microsievert) from radon included in the air (* such  as inhalation of radioactive gases. These are radiation received from inside human bodies (* called “internal exposure”).
  • It shows that radiation also comes from the foodstuffs that exist in the nature and that we live while being exposed to radiation from inside our body.
  • There is a regional difference between the amounts of such natural radiation. In the region of Guarapari, Brazil, it amounts to 10,000 microsieverts (10 millisieverts), four times more than the world average. (* This is the amount of external exposure.)

Keywords: amount of radiation received from medical care, dose limit for the general public

  • You can also see the amount of radiation received from medical  care (* called “medical exposure”) on the right side of Fig. 1. It is said that the group examination of chest X-ray gives radiation of 50 microsieverts per examination, the group examination of stomach X-ray gives 600 microsieverts (0.6 millisieverts) and the chest X-ray computerized tomography scan (CT scan) 6,900 microsieverts (6.9 millisieverts) per examination.
  • It is better not to receive radiation if the circumstances permit. The idea is to compare the “loss” of receiving radiation with the “gain” of detecting a failure or seeking reassurance and determine that a certain level of “loss” is permissible.
  • Therefore, the amount of radiation from medical care is treated separately from other sources. In the middle of the right hand of Fig. 1, you can see a description of “Dose limit (annual) of the general public” which is 1,000 microsieverts/year. The dose means the amount of radiation received by human bodies. Therefore, this section means that the “limit of amount of radiation received by the general public in a year is set to 1,000 microsieverts (1 millisievert).” However, it is followed by a mention “except medical care,” indicating that the value of 1,000 microsieverts (1 millisievert) refers to the amount of radiation received by other means than medical care.

Keywords: dose, dosimeter, operator

  • On the other hand, while it is true that the “limit of amount of radiation received by the general public in a year is set to 1,000 microsieverts (1 millisievert.),” there is no way to control the dose as there is no one who carries a dosimeter (an instrument designed to measure the amount of radiation) around the clock throughout the year. It is all the more so since we receive 2,400 microsieverts (2.4 millisieverts) that exceed the 1,000 microsieverts (1 millisievert) as natural background as a global average and there is also a regional difference.
  • In fact, the criteria of “the limit of amount of radiation received by the general public in a year is set to 1,000 microsieverts (1 millisievert)” is not intended to regulate the individuals of the general public, but the corporate bodies, i.e., nuclear power stations and other facilities where radiation or radioactive substances (substances that emit radiation) are treated such as hospitals, laboratories and factories. In  other words, the criteria means that “the corporate bodies shall ensure that “in addition to the natural radiation and  that from medical care, the individuals of the general public will not receive radiation of more than 1,000 microsieverts (1 millisievert) even if they stay where they are supposed to be (for example, at the  boundary of a  hospital site and an area where the members of the general public live) throughout the year.”

Keywords: influence of nuclear accident, μSv/h, microsieverts per hour

  • To consider the influence from the accident of the nuclear power station, let’s look at Table 1 that indicates the results of measurements of environmental radiation taken in various parts of the country. The unit of measure “μSv/h (microsieverts per hour)” is the amount of radiation (microsieverts) per hour.
  • The rightmost field shows a range of radiation measured during normal hours in the past. You may recognize a regional difference that amounts to  about two times even in Japan as well as a variation in time at the same measurement point. Roughly, it is usually in the order of 0.05 microsieverts  per hour.
  • Now, there is a measurement point at which a value of  1.035 microsieverts per hour was recorded. Although it was then returning to normal, if this value of 1.035 microsieverts per hour continued for a year, which is only an assumption, not a reality, the calculated cumulative radiation received for the one year time would be 9,066.6 microsieverts as a year consists of 8,760 hours. (* This does not include the internal exposure that is radiation from inside the body.) When this value is compared with the values indicated on Fig. 1, it follows that it is an amount of radiation a little smaller than that of the annual natural radiation at Guarapari, Brazil. It is a little more than one chest X-ray CT and one stomach X-ray examination each.

Keywords: radiation limit for special cases, radiation worker, in case of emergency work, International Commission on Radiological Protection (ICRP), International Atomic Energy Agency (IAEA), standard value acceptable to the general public in case of emergency, planned evacuation zone

  • We have so far looked at the radiation levels experienced during our daily life.

The radiation limit for special cases is indicated on the upper part of Fig. 1. The upper limit allowed to radiation workers and personnel of police and fire fighting agencies involved with disaster countermeasures is 50,000 microsieverts (50 millisieverts) annually. The upper limit allowed  to emergency work was set at 100,000 microsieverts (100 millisieverts) annually, but it has been raised to 250,000 microsieverts (250 millisieverts) annually in the wake of the accident at Fukushima Daiichi.

  • Then, what about the individuals of the general public? Does the radiation limit remain to be 1,000 microsieverts (1 millisievert) annually after the accident? The limit allowed to the individuals of the general public in case of emergency is set at 20,000 – 100,000 microsieverts (20 – 100 millisieverts) annually by the international rulemaking organizations, the International Atomic Energy Agency (IAEA) and the International Commission on Radiological Protection (ICRP).
  • The “planned evacuation zone” set by the government is the area in which  the amount of radiation received by the individuals of the general public in a year could reach the level of 20,000 microsieverts (20 millisieverts),  the lowest value of  the above-mentioned range, if the current radiation level (as of April 5 at 24:00) continued in addition to the  radiation level experienced just after the accident.
  • The preceding discussions may help you determine which is within daily range and which is the limit for special cases in terms of the amount of radiation received by human beings (values in microsieverts).

Unit of “Becquerel”

Keywords: radioactivity, radioactive substance

  • The word “Becquerel (Bq)” has become popular. It is a unit of measure for “radioactivity.”
  • The substances that emit radiation is called “radioactive substance” and “radioactivity” is a measure of how strong the capacity of  such substances is to emit radiation. You are right to say as follows: “A radioactive substance of 100 Becquerels emits 100 times more radiation than one of 1 Becquerel.”
  • As far as the same radioactive substance is concerned, the amount and radioactivity are proportional. So it is reasonable to say, “Radioactivity equals to the amount of the radioactive substance.”

Keywords: 40 Becquerels per square centimeter (40 Bq/cm2), 300 Becquerels per kilogram (300 Bq/kg), contamination, decontamination

  • The expressions such as “40 Becquerels per square centimeter (40 Bq/cm2)” or “300 Becquerels per kilogram (300 Bq/kg)” have also become popular. The former is used when radioactive substances are attached to the surface of a human body or foodstuffs and the latter when radioactive substances have entered the whole or part of foodstuffs or water.
  • The state where radioactive substances are attached to or enter as above is expressed as “contaminated.” However, foodstuffs and water inherently have radioactive substances during normal times, albeit in a very small quantity. So the word “contamination” refers to the state where the amount of radioactive substances has increased compared with the normal times.
  • When radioactive substances are attached to the surface (*called surface contamination), it is possible to eliminate contamination by wiping or water washing. This operation is called “decontamination” (*For comparison, the level of screening or level of contamination at which decontamination is required for surface contamination of the general public who visit a  local health care center for checkup examination is 100,000 cpm when measured by a survey meter, i.e. 100,000 counts per minute. It corresponds to the surface contamination level of 400 Becquerels per square centimeter (400 Bq/cm2), when a GM survey meter, most typical counter, is used.)

Keyword: drinking water or foodstuff, interim regulation limit, Food Sanitation Law, index, radioactive iodine, cow milk, greenstuffs, fish and  shellfish,  tap water

  • Referring to the previous item, at what Becquerel level should we be careful?

It is defined as national criteria by laws and regulations.

  • For radioactive substances contained in drinking water and foodstuff, the “interim regulation limit” is defined by the Ministry of Health, Labour and Welfare based on the index provided by the Nuclear Safety Commission. The foodstuffs that exceed the limit are stipulated in the Food Sanitation Law to avoid ingestion as food. Drinking water is also regulated using indices for ingestion.
  • Such limits for radioactive iodine, for example, are 300 Bq/kg for drinking water and cow milk, 2,000 Bq/kg for greenstuffs (except edible roots and potatoes) and fish and shellfish and 300 Bq/kg for other than infants and 100 Bq/kg for infants for drinking water. (* For details, see the “Q & A” Section on the web site of the Food Safety Commission.)

Keyword: Regulation of shipment and water intake, thyroid, International Commission on Radiological Protection (ICRP)

  • Although the above values are announced, ordinary people cannot judge whether those foodstuffs and drinking water are safe or not, because they cannot measure. However they do not need to think they should measure and judge by themselves. They cannot eat and drink foodstuffs and water which exceed the regulation limits and indices, because shipment and  intake  of such foodstuffs and water are restricted by the laws and regulations.
  • How is this regulation limit defined? Let’s take radioactive iodine as an example. Assume that the condition continues for a whole year in which the same concentration of radioactive iodine as the regulation limit is contained   in food and drink. Besides, suppose that you take the average amount of drinking water and foodstuffs such as cow milk and dairy products,  vegetables, cereals, meat, eggs and fish and others for a year. In this case, the radiation received by the thyroid during the year will be 50 millisieverts. Conversely, the limit of 50 millisieverts will not be reached as long as you eat and drink food and water below the regulation limit. The reason why  the thyroid is focused on is because iodine is concentrated on the thyroid by nature. And the reason why the value of 50 millisieverts is set as a limit is because the radiation limit of the thyroid for iodine for a year is set at 50 millisieverts based on the recommendations of the rulemaking International Commission on Radiation Protection (ICRP).
  •  For those concerned that the regulation limit may have been exceeded temporarily by eating and drinking, it is a good idea to recall that the  regulation limit has been set according to the strict conditions as mentioned above.

Countermeasures to avoid radiation as far as possible

Keyword: recommendation for indoor evacuation

  • The following advices are offered for the regions where indoor evacuation is recommended:
  • Remain indoors as much as possible.
  • Avoid going out unnecessarily.
  • Avoid being exposed to the rain.
  • Brush off the clothes before getting in the house.
  • Wear a mask while you are out.

Keyword: three principles to reduce effects of radiation; shielding, distance and time; indoors and outdoors

  • Why is it possible to avoid receiving excessive radiation if these advices are followed? First, be aware of the Three Principles of “Shielding, Distance and Time” to reduce effects of radiation.
  • The “Shielding” means “something to shield with.” Radiation loses its intensity after it passes through an object. It sometimes settles inside the object. It is similar to the fact that the intensity of light is smaller when you see the light through a piece of paper than directly. It is also similar to the fact that you do not see the light anymore if the paper is too thick. You are  safer indoors than outdoors since the roof and structure of a building also shield radiation.
  •  The next factor is “Distance.” The intensity of radiation weakens if you are far from the source of radiation, in other words, if the distance is longer. It is similar to the fact that the light of a candle looks brighter when you look at  it  up close, but that it loses its brightness when you are away from it. When radioactive substances are blown by the wind and fall on the roof, they are sometimes deposited on the roof or the ground surrounding the building temporarily. You can take a distance from these radioactive substances if you stay indoors.
  •  It is said that, if the effects of “Shielding” and “Distance” are combined, the level of radiation received drops to a fraction or one-tenths if you stay indoors compared to outdoors.
  •  The effect of “Time” is also important. The unit “μSv/h (microsieverts per hour)” that is frequently mentioned on TV or newspapers is the amount of radiation (microsieverts) per hour. For example, if you stay at a place with 1 microsievert per hour for an hour, you receive radiation of 1 microsievert. If  you stay only for thirty minutes, the amount of radiation received decreases to a  half, 0.5 microsieverts. That is why it is recommended to stay outdoors for as short a time as possible when the amount of radiation is larger outdoors than indoors.

Keyword: rain, mask, measures against hay fever

  •   The next advice “Avoid being exposed to the rain and Brush off the clothes before getting in the house” are intended to prevent radioactive substances dissolved in the rain, coming on the wind or stirred up from the ground from being attached to and remaining on the surface of clothes.
  •   The advice “Wear a mask while you are out” is designed to avoid sucking and ingesting radioactive substances present in the air.
  •   The advices “Brush off the clothes before getting in the house” and “Wear a mask while you are out” are the same measures as against hay fever.

Keyword: areas free from evacuation order or recommendation for indoor evacuation, National Institute of Radiological Sciences, less than 100 millisieverts, cancer, monitoring data, regional difference, difference of natural radiation among domestic measuring points, maximum difference among prefectural averages, daily level

  • The recommendations for indoor evacuation have been described. How

should we respond in the areas other than those subject to evacuation order  or recommendation for indoor evacuation?

  •     The web site of the National Institute of Radiological Sciences, an incorporated administrative agency engaged in specialized research into radiation medicine and effects of radiation on human bodies, states  that  “there is no scientific evidence that the amount of radiation exposed (Writer’s note: amount of radiation received) of about less than 100 millisieverts leads to cancer” and that “the effects of radiation do not  deserve  excessive concerns as they are much lower compared with the risk associated with lifestyle habits such as smoking and diet. In addition, outside the evacuation zone surrounding the nuclear power station, it would not be a cause for concern if you live in an ordinary way since the value of 100 millisieverts will not be exceeded as long as you live as usual.”
  •   If you are still anxious about it, it is a good idea to determine if you should take measures as taken in the area subject to indoor evacuation by reviewing the monitoring data presented by the Ministry of Education, Culture, Sports, Science and Technology and each prefecture (amount of radiation outdoors by region: microsieverts per hour.)
  •   When, for example, a calculation is made based on 8,760 hours for  a  year, the value of 100 millisieverts is reached if a value of 11.4 microsieverts per hour in the monitoring data persists for a whole year.
  •   The monitoring data shows a value in the order of 0.05 microsieverts per  hour although there is a regional difference. Let’s assume a case when a tenfold value of 0.55 microsieverts per hour continues for a month before returning to the normal value. The increment observed during this period is 360 microsieverts. Now, look at the middle part on the left of Fig. 1, which shows that the “difference of natural radiation among domestic measuring points (annual)” (maximum difference among prefectural averages) is 400 microsieverts/year. While only on paper, the amount of radiation may  be higher than the above-mentioned 360 microsieverts if you move from an area with low natural radiation level to one with a higher natural radiation level. Such increase and decrease in the amount of radiation may be deemed as a daily fluctuation.

Keyword: food contamination, regulation of shipment and water intake, radioactive iodine

  •   Some may be concerned about food contamination. We cannot eat food or drink tap water if the level of radiation has exceed the regulation limit set by the government since its  shipment and water intake are controlled, as previously stated.
  •   For those who are still concerned, the following advice posted on the  web  site of the National Institute of Radiological Sciences may provide some hints.
  • Almost all radioactive substances detected on vegetables are considered to be attached to their surface. Therefore, washing, boiling (and disposing of the water), peeling of skin and trimming-off of the green tops may reduce contamination.
  • Radioactive iodine may not vanish even if the vegetables are boiled. Rather,  it may be concentrated as the water evaporates.

(Writer’s note: For vegetables, boiling them helps removing radioactive substances present inside or on the surface of vegetables into the water. For drinking water, however, boiling is not a solution, since the radioactive  substances remain in the water while the amount of water decreases by evaporation and their concentration becomes higher.)

Keyword: thyroid, stable iodine tablet, radioactive iodine, stable iodine, side effect, physician’s order, government’s order

  •   Stable iodine tablets are said to work as a means of preventing the thyroid from receiving radiation. Iodine is classified into radioactive iodine that releases radiation and stable iodine which is in a stable form that does not release radiation.
  •   Iodine is concentrated on the thyroid by nature. Both radioactive and stable iodine share the same property as iodine. For this reason, the idea is that, if stable iodine tablets are taken before or just after the radioactive iodine is ingested to fill the thyroid with it, no or little radioactive iodine will enter and the amount of radiation will be less. That is the mechanism of the  stable  iodine tablets.
  • It is deemed important, however, to take them in accordance with the physician’s order when they are distributed in evacuation centers since they may pose a risk of side effects such as allergy.
  • In addition, if they are taken long before the ingestion of radioactive iodine is suspected, the stable iodine will be discharged from the body,  resulting in poor efficacy.
  •   It is recommended to take them in accordance with the instructions from the government or other competent authorities.

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