Radiation surrounds us. Detectable amounts occur naturally in soil, rocks, water, air, and vegetation but large doses can have dramatic and life changing effects. There are different kinds of radiation but it is ionising radiation that can cause damage to living tissue at high levels, making it vital to control our exposure to it.
Radiation exposure depends on three factors, the:
- strength of the radiation source
- distance you are from it
- duration of the exposure
Exposure to high levels of ionising radiation can result in mutation, radiation sickness, cancer, and death but when used in medical applications it can be used to prolong life. Ionizing radiation is invisible and not directly detectable by human senses, unless at very high doses, so instruments such as Geiger counters are necessary to detect its presence.
One way to measure radiation is to measure the dose of radiation received, i.e. the effect it has on human tissue, which is measured in sieverts, abbreviated as Sv.
As 1 sievert represents a very large dose smaller units are more commonly used;
- Millisieverts, one thousandth of a sievert and abbreviated as mSv (1000mSv = 1Sv)
- Microsieverts, one millionth of a sievert and abbreviated as uSv (1,000,000uSv = 1Sv)
Dosimeters generally measure in microsieverts.
An older unit for dose is the rem (Roentgen Equivalent in Man), or the smaller millirem (abbreviated “mrem”) still often used in the United States. One sievert is equal to 100rem.
Roentgen’s are another measure, 1 Roentgen (R) equals 0.877 rem or 0.00877 Sieverts.
It can be hard to predict the impact of radiation on humans but around half of all those exposed to 5 sieverts will die from it. Almost all who receive a dose of 10 sieverts will die within weeks.
A typical dose for those workers who died within one month of the disasters was 6 sieverts.
During the Chernobyl disaster four hundred times more radioactive material was released than at the atomic bombing of Hiroshima.
The global average exposure of humans to ionizing radiation is about 2.4 – 3mSv (0.0024-0.003Sv) per year, 80% of which comes from nature. The remaining 20% results from exposure to human-made radiation sources, for example medical imaging (X-rays, CT scans etc).
In Europe, average natural background exposure by country ranges from under 2mSv annually in the United Kingdom to more than 7mSv annually in Finland.
The U.S. Nuclear Regulatory Commission (NRC) requires that its licensees limit human-made radiation exposure for individual members of the public to 1mSv per year, and limit occupational radiation exposure to adults working with radioactive material to 50mSv per year (3-25 uSv/hr).
|Event||Radiation reading, millisievert (mSv)|
|Single dose, fatal within weeks||10,000.00|
|Typical dosage recorded in those Chernobyl workers who died within a month||6,000.00|
|Single does which would kill half of those exposed to it within a month||5,000.00|
|Single dosage which would cause radiation sickness, including nausea, lower white blood cell count. Not fatal.||1,000.00|
|Accumulated dosage estimated to cause a fatal cancer many years later in 5% of people||1,000.00|
|Max radiation levels recorded at Fukushima plant 15 March 2011, per hour||400.00|
|Exposure of Chernobyl residents who were relocated after the blast in 1986||<100.00|
|Recommended limit for radiation workers every five years||100.00|
|Lowest annual dose at which any increase in cancer is clearly evident||100.00|
|CT scan: heart||16.00|
|CT scan: abdomen & pelvis||15.00|
|Dose in full-body CT scan||10.00|
|Airline crew flying New York to Tokyo polar route, annual exposure||9.00|
|Natural radiation we’re all exposed to, per year||2.00|
|CT scan: head||2.00|
|Radiation per hour detected at Fukushimia site, 12 March 2011||1.02|
|Mammogram breast x-ray||0.40|
The Guardian (Sources: WNA, Reuters, radiologyinfo.org)
Main environmental pathways of human radiation exposure
Source: The International Chernobyl Project – Technical Report (PDF) – Assessment of Radiological Consequences
and Evaluation of Protective Measures – Report by an International Advisory Committee 1991
Geiger counters are used to detect ionizing radiation. The primary component of the Geiger counter is a tube filled with an inert gas that conducts electricity when struck by radiation. This allows the gas to complete an electrical circuit. Whilst older models typically included a moving a needle many now feature an LCD display to display levels. Nearly all make an audible warning sound. Geiger counters can measure radiation in a variety of units, depending on the application.
Often confused with geiger counters, an ion chamber is an extremely simple device that can also detect ionizing radiation. The basic chamber is a simple metal tube with a wire electrode at the centre that is well insulated from the walls. The chamber is generally filled with dry air but using gasses like carbon dioxide can increase sensitivity. A DC voltage is applied between the outer can and the centre electrode to create an electric field that sweeps the ions to the oppositely charged electrodes. The centre wire is held near zero volts and the resulting current in the centre wire is measured.
One of the first pieces of measuring equipment the army sent to Chernobyl to evaluate the situation was a DP-3. The DP-3 was developed for use in military helicopters and armoured vehicles. Far less sensitive than a geiger counter, they measured from 0 to 500 roentgens per hour. If your DP-3 indicates radiation it’s time to run! More information here.
The situation at the plant by the evening of April 26 remained unclear. Therefore, on the night of 26 -27 April, Colonel-General VK Pikalov organised a patrol to measure radiation levels at reactor 4, at the plant in general and in the town of Pripyat. A BRDM-PX special armoured vehicle circled block 4, measuring radiation levels, which in some places exceeded 500 R / hr (the limit of the DP-3).
Levels of radiation at Chernobyl
Levels of radiation immediately after the explosion
The radiation levels in the worst-hit areas of the reactor building, including the control room, have been estimated at 300Sv/hr, (300,000mSv/hr) providing a fatal dose in just over a minute.
The reactor staff struggled to establish the levels of radiation following the explosion as one dosimeter capable of measuring up to 9Sv per second 1,000 R/s was buried in the wreckage, and another one failed when it was turned on. All the remaining dosimeters had limits of 0.001 R/s (0.3 µA/kg) 30mSv/hr and read “off scale”. The reactor staff could therefore only ascertain that the radiation levels were somewhere above 30mSv/h while in reality the true levels were far higher.
Because of the inaccurate low readings, the reactor crew chief Alexander Akimov assumed that the reactor was intact. The evidence of pieces of graphite and reactor fuel lying around the building where ignored, and the readings of another dosimeter brought in at 04:30am were dismissed under the assumption that the new dosimeter must have been defective. Akimov stayed with his crew in the reactor building until morning, sending members of his crew to try to pump water into the reactor. None of them wore any protective gear. Most, including Akimov, died from radiation exposure within three weeks.
22 years after the explosion radiation levels inside the reactor hall were approximately 34 Sv/hr – a lethal dose in 10-20 minutes.
Shortly after the explosion firefighters arrived to tackle the fire. First on the scene was the Chernobyl Power Station firefighter brigade under the command of Lieutenant Volodymyr Pravik, who died on 9 May 1986 of acute radiation sickness. They were not told how dangerously radioactive the smoke and the debris were, and may not even have known that the accident was anything more than a regular fire:
“We didn’t know it was the reactor. No one had told us.”
Grigorii Khmel, the driver of one of the fire engines, later described what happened:
“We arrived there at 10 or 15 minutes to two in the morning…. We saw graphite scattered about. Misha asked: “Is that graphite?” I kicked it away. But one of the fighters on the other truck picked it up. “It’s hot,” he said. The pieces of graphite were of different sizes, some big, some small, enough to pick them up…”
“We didn’t know much about radiation. Even those who worked there had no idea. There was no water left in the trucks. Misha filled a cistern and we aimed the water at the top. Then those boys who died went up to the roof – Vashchik, Kolya and others, and Volodya Pravik…. They went up the ladder … and I never saw them again.”
However, Anatoli Zakharov, a fireman stationed in Chernobyl since 1980, offers a different description:
I remember joking to the others, “There must be an incredible amount of radiation here. We’ll be lucky if we’re all still alive in the morning.”
Twenty years after the disaster, he said the firefighters from the Fire Station No. 2 were aware of the risks.
Of course we knew! If we’d followed regulations, we would never have gone near the reactor. But it was a moral obligation – our duty. We were like kamikaze
Approximate radiation levels in and around Unit 4 shortly after the explosion:
|Location||Sieverts per hour (SI Unit)|
|Vicinity of the reactor core||300|
|Debris heap at the place of circulation pumps||100|
|Debris near the electrolyzers||50-150|
|Water in the Level +25 feedwater room||50|
|Level 0 of the turbine hall||5-150|
|Area of the affected unit||10-15|
|Water in Room 712||10.00|
|Nearby concrete mixing unit||0.10–0.15|
Source B. Medvedev (June 1989).”JPRS Report: Soviet Union Economic Affairs Chernobyl Notebook”.
Levels of radiation in Pripyat and Chernobyl now
The levels of radiation as measured in 2009 (Radiation levels can, and do, fluctuate depending on a number of factors.)
|“Lazurny” swimming pool||0.9|
|Pripyat kindergarten “Golden Key”||0.8|
|Pripyat 1970 monument||11.5|
|Hospital No 126||0.7 above ground
0.8 – 382+ in the basement
|Palace of culture||0.8|
|Middle School Number 3||0.7|
|Middle School Number 1||0.7|
|Cooling towers||1.5 Inside
12.6 to the rear
|16 storey tower block||0.9 roof|
|Fish laboratory||1.6 outside
1.3 by the fire engine
|Jupiter factory||0.5 outside
0.7 – 1.6 inside
|Yanov Railway Station||0.3|
|Reactor 4||2.4 – 2.6 surrounding roads|
|Pripyat cemetery||14 – 22|
|Residential houses Chernobyl||0.2|
|Cafe Pripyat||13.6 on steps|
|Metal claw used in the clean up||336|
Generally the levels of radiation in Pripyat and the surrounding area, although far higher than the norm, are safe for the time you will be exposed to them (just don’t go licking stuff).
Those who work within the zone typically work 3 weeks on, 3 weeks off. The “off” period must be spent outside of the zone.
Radiation levels can change daily, dependent upon a number of factors including wind speeds. Just because you measured a level yesterday doesn’t mean it’ll be the same today as pockets of radiation move around. Large variations in levels can also occur within only a few metres of each other.
Weather cleansed tarmac, or hard standing, is preferable to standing on vegetation. Pay specific attention to moss, wherever it may grow, as it is great at absorbing radiation and therefore likely to emit far higher levels than the surface it is growing on. This sounds simple in theory but I found it easy to forget when confronted with the sights of Pripyat.
It depends on the nature of your visit but for longer, less chaperoned, trips it may be worth borrowing or buying a Geiger counter. I didn’t have one but many of those I went with did. All gave slightly different readings but functioned as a good guide. Clearly it’s pointless having one if you don’t know what the readings actually mean, accurate or not, partly why I didn’t take one on my first visit.
Dust is a potentially nasty. Ingesting radioactive particles is not something you want to make a habit of. I choose not to wear a mask. The majority of people I saw also didn’t but obviously make your own decision, it’s your health.
Rooms open to the elements, the majority now are, tend to have lower levels of radiation than those still enclosed by doors and windows. The basement of the hospital contains the clothing of those who first tackled the explosion. Located in an enclosed environment even after 25 years the clothing is highly radioactive (way in excess of 386 uSv/h) and a terrifying reminder of what those first on the scene faced. If you do venture down there I recommend you don’t hang around and wear at least a correctly rated mask that covers both nose and mouth. A hazmat suit you can bin afterwards may also be wise. I didn’t have a mask and therefore chose not to go down there, a decision I don’t regret.
High levels or radiation (336 uSv/h) can also be found towards the rear of the claw used in the clean up. Although decontaminated they clearly missed a bit.
Most of Pripyat was decontaminated in the weeks following the explosion however the graveyard is one exception (14-22 uSv/h), it being hard to remove topsoil and keep graves intact, and therefore we spent only 15 minutes on site.
I ate and drank in Pripyat but generally only within the minibus and I was conscious not to touch the food directly with my hands. There seemed to be an unwritten rule that all accompanying officials must light a cigarette upon exiting a vehicle in the Zone.
The clothing I wore, including footwear, I either binned or double washed on my return home. It’s easy to become blasé out there but if you’re unpacking footwear caked in zone mud at home it soon focuses the mind. The clothing I took home I wrapped and sealed in several bin bags.
The spread of radiation
Following the explosion at Chernobyl approximately 100,000 km² of land was significantly contaminated with fallout, the worst hit regions being in Belarus, Ukraine and Russia. Lower levels of contamination were detected over all of Europe.
The initial evidence that a major release of radioactive material was affecting other countries came from Sweden, where on the morning of 28 April workers at the Forsmark Nuclear Power Plant approximately 1,100 km (680 mi) from the Chernobyl were found to have radioactive particles on their clothes.
The rise in radiation levels had already been measured in Finland, but a civil service strike delayed the response and publication.
It was Sweden’s search for the source of radioactivity, once they had ruled out a leak at the Swedish plant itself, that at noon on 28 April led to the first hint of a serious nuclear problem in the western Soviet Union. The evacuation of Pripyat having already taken place by this point.
Areas of Europe contaminated with 137Cs
|Country||37–185 k Bq/m2||185–555 kBq/m2||555–1480 kBq/m2||>1480 kBq/m2|
|km2||% of country||km2||% of country||km2||% of country||km2||% of country|
|Totals||162,160 km2||19,100 km2||7,200 km2||3,100 km2|
Radioactive fallout from the Chernobyl accident was scattered depending on the weather conditions. Much was deposited on mountainous regions such as the Alps and the Welsh and the Scottish Highlands, through rainfall. Sweden and Norway also received heavy levels of fallout.
Rain was purposely seeded over 10,000 km2 of the Belorussian SSR by the Soviet air force to remove radioactive particles from clouds heading toward highly populated areas. Heavy, black-coloured, rain fell on the city of Gomel just over the Belarus border.
Reports from Soviet and Western scientists indicate that Belarus received about 60% of the contamination that fell on the former Soviet Union. However, the 2006 TORCH report stated that half of the volatile particles had landed outside Ukraine, Belarus, and Russia. Studies carried out in surrounding countries indicate that over one million people could have been affected by radiation.
The release of radiation
The nature of the radiation released was dependent on the physical and chemical properties of the radioactive elements in the core. Particularly dangerous were the highly radioactive fission products, those with high nuclear decay rates that accumulate in the food chain, such as the isotopes of iodine, caesium and strontium. Iodine-131 and caesium-137 are responsible for most of the radiation exposure received by people.
The release of radioisotopes from the nuclear fuel was partly dependent on their boiling points, and the majority of the radioactivity present in the core was actually retained in the reactor.
- All of the noble gases, including krypton and xenon, contained within the reactor were released immediately into the atmosphere by the first steam explosion.
- 50 to 60% of all core radio-iodine in the reactor was released, as a mixture of vapor, solid particles, and organic iodine compounds with a half-life of 8 days.
- 20 to 40% of all core caesium-137 was released in aerosol form. Caesium-137, along with isotopes of strontium, are the two primary elements preventing the Chernobyl exclusion zone from being re-inhabited. Cs-137 has a half-life of 30 years.
- An estimated 1150 PBq of Tellurium-132, half-life 78 hours, and 5200 PBq of Xenon-133, half-life 5 days, was released.
- An early estimate for total nuclear fuel material released to the environment was an emission of 6 t of fragmented fuel.
Cesium-137 is a radioactive isotope of caesium which is formed by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nuclear weapons. It is among the most problematic of the short-to-medium-lifetime fission products because it easily moves and spreads in nature due to the high water solubility of caesium’s most common chemical compounds, which are salts.
Cesium-137 has a half-life of approximately 30 years. As of 2005, caesium-137 is the main source of radiation in the Exclusion Zone around the nuclear power plant. Together with caesium-134, iodine-131, and strontium-90, caesium-137 was among the isotopes distributed by the reactor explosion that posed the greatest risk to health. It is Cesium-137 that has led some reindeer and sheep in Scandinavia to exceed the Norwegian safety limit 26 years after the disaster.
In April 2011, elevated levels of caesium-137 were also being found in the environment after the Fukushima Daiichi nuclear disasters in Japan. Caesium-137 in the environment is human-made. Unlike most other radioisotopes, caesium-137 is not produced from the same element’s nonradioactive isotopes but as a byproduct of the nuclear fission of much heavier elements, meaning that until the building of the first artificial nuclear reactor, the Chicago Pile-1, in late 1942, it had not occurred on Earth for billions of years.
Health of plant workers and local people
In the aftermath of the accident, 237 people suffered from acute radiation sickness (ARS), of whom according to World Health Organization’s 2006 report, 28 died within the first three months. Most of the victims were the firemen and rescue workers first on the scene.
No further ARS-related deaths were identified in the general population affected by the disaster. Of the 72,000 Russian Emergency Workers being studied, 216 non-cancer deaths are attributed to the disaster, between 1991 and 1998. Of all the 66,000 Belarusian emergency workers, by the mid-1990s only 150 (roughly 0.2%) were reported by their government as having died. In contrast, 5,722 casualties were reported among Ukrainian clean-up workers up to the year 1995, by the National Committee for Radiation Protection of the Ukrainian Population.
The latency period for solid cancers caused by excess radiation exposure can be 10 or more years; so at the time of the WHO report being undertaken, the rates of solid cancer deaths were no greater than the general population.
Acute radiation syndrome
Acute radiation syndrome (ARS), also known as radiation poisoning, radiation sickness or radiation toxicity, is a number of health effects which occur within 24 hours of exposure to high amounts of ionising radiation.
The radiation causes cellular degradation due to destruction of cell walls and other key molecular structures within the body and it is this destruction that causes the symptoms. The symptoms can begin within one or two hours and may last for several months. The term refers to acute medical problems rather than ones that develop after a prolonged period.
The onset and type of symptoms depends on the radiation exposure. Relatively smaller doses result in gastrointestinal effects such as nausea and vomiting and symptoms related to falling blood counts such as infection and bleeding. Relatively larger doses can result in neurological effects and rapid death. Treatment of acute radiation syndrome is generally supportive with blood transfusions and antibiotics, with some more exotic treatments such as bone marrow transfusions being required in extreme cases.
Similar symptoms may appear months to years after exposure as chronic radiation syndrome when the dose rate is too low to cause the acute form. Radiation exposure can also increase the probability of developing some other diseases, mainly different types of cancers. These diseases are sometimes referred to as radiation sickness, but they are never included in the term acute radiation syndrome.