The emission of ionizing radiation or particles caused by the spontaneous disintegration of atomic nuclei is called radioactivity. Radiation can be classified as electromagnetic radiation such as radio waves, heat and x rays; particle radiation such as alpha, neutron and beta radiation; acoustic radiation such as seismic waves, sound and ultrasound; and gravitational radiation.

It can also be classified into ionizing or non-ionizing based on the radiated particle’s energy. Radioactive materials that release α, β or γ radiation are the common sources of ionizing radiation. Visible light, microwaves and infrared light are the common sources of nonionizing radiation.

The world around us is naturally radioactive in many ways.Radioactive elements, such as plutonium and uranium, are mined from deep below the earth's surface. They are enriched and harnessed to produce electricity and nuclear weapons and then disposed of, making them extremely harmful to humans, animals, plants and the environment alike. Another kind of natural radioactivity includes species produced in small amounts in the upper atmosphere due to cosmic ray bombardment. Even though radiation has few advantages, exposure to radioactive substances even for a small duration of time can pose a high risk to health. The extent of the damage depends upon the amount and duration of the exposure. A very large amount of radiation exposure can cause sickness or even death within hours or days.

Here is the list of the most radioactive places on earth.

Fukushima, Japan: In March 2011, a 9-9.1 magnitude earthquake triggered a tsunami on the Pacific coast of Japan, resulting in the worst nuclear disaster since Chernobyl. As a result, three of the Fukushima Daiichi Nuclear plant’s six reactors melted down and an enormous amount of radiation leaked into the surrounding sea.Radioactive material linked to the disaster was found as far as 200 miles away from the power plant. Scores of people have died and thousands became homeless.It is estimated that it will take four decades to completely decommission the nuclear plant. As the incident occurred recently, it is the most radioactive place on the earth currently.













Image: Fukushima I nuclear power plant before the 2011 explosion. Photo courtesy of KEI/Wikipedia.

Chernobyl, Ukraine: In April 1986, an explosion at the Chernobyl Nuclear Power Plant in Ukraine led to the release of a large quantity of radioactive material into the air and atmosphere, resulting in the death of approximately 93,000 people. The disaster released radiation which was 100 times more than the Nagasaki and Hiroshima bombs. A total of six million people are estimated to have been exposed to the radiation, which spread across Europe and the USSR. Belarus absorbed more than 70% of the radiation. Around $18bn was spent to control the damage.There is an Exclusion Zone of 2,600 km2 surrounding the Chernobyl plant, which is still closed from public access. Cleanup efforts are still underway, but it will be several decades before people will be able to return to the area for settlement.













Image: View of Chernobyl power plant taken from the roof of a residential building in Pripyat, Ukraine. Photo courtesy of Jason Minshull/Wikipedia.

Mailuu-Suu, Kyrgyzstan: Mailuu-Suu is a mining town in Jalal-Abad Region of southern Kyrgyzstan. Unlike in other places, here radiation is not due to nuclear power plants or bombs, but due to mining for uranium. Soviet Union, which had set up a mining facility, buried around 10,000 tons of uranium ore in the excavated areas. It currently has 1.96 million cubic meters of Uranium wastewith 26 waste dumps near the city boundary, which still occupied by close to 23,000 people. The region is also a hot-spot for seismic activity, which only increases the risk of radioactive material contaminating the region further.

Siberian Chemical Combine, Russia: The Siberian Chemical Combine plant,which is only about 3,000 km away from Moscow, was used in the USSR's nuclear research program to enrich uranium and plutonium for about 40 years. Later it was transformed into a storage site for solid toxic chemical and radioactive waste.Todaythousands of liters of liquid wastelie uncovered in pools and 113,000 metric tons of solid radioactive waste is stored in leaking containers. As a result, high mortality rates were recorded in the surrounding wildlife and local community was destroyed.

The Polygon (Semipalatinsk test site), Kazakhstan: The Polygon, which is also known as the Semipalatinsk test site,was one of the main sites for testing nuclear weapons by the Union of Soviet Socialist Republics (USSR) during the cold war era. It is estimated that more than 450 nuclear testswere carried out in the areafrom 1949 to 1989. Even though a staggering 700,000 people actually live in the area, the government deemed it to be uninhabited. Because of the largest concentration of nuclear explosionsalmost 200,000 people are still suffering from the adverse effects of radioactivity.

Sellafield, UK: Sellafield was constructed in 1940 on the western coast of England to manufacture plutonium for atomic weapons. During its peak period, the plant released eight million liters of toxic radioactive waste water into the Irish Sea every day.In 1957, a huge fire ravaged the plutonium enrichment plantfor three days and massive amounts of radioactive fumes were released into the atmosphere. The incident earned its place as the worst nuclear accident in the UK’s history and came to known as – The Windscale Fire.It was linked to 240 cases of cancer.












Image: Storm Clouds over Sellafield. Photo courtesy of Chris Eaton/Wikipedia.

Hanford, USA: The Hanford nuclear production complex was built in 1943 as part of the Manhattan Project. The US produced enriched plutonium in the plant to make majority of its 60,000 nuclear weapons. In the process, the facility led to the creation of large amount of radioactive waste. Even though the US government tried its best to mitigate the adverse effects by decommissioning the power plant, the area still accounts formore than 65% of the country’s highly radioactive waste, both in solid and liquid form.It contaminated 200 mi2 of groundwater, making the power plant the most radioactive place in the US.

The Somali Coast: During the 1980s several Swiss and Italian firms and even a particular section of Italian mafia took advantage of lax Somali regulations and secretly dumpedradioactive hospital rubbish, nuclear waste and toxic metalson the coast. The effect of this radioactive material can be still seen as birth defects and cancer are common in the area.

Mayak, Russia: The Mayak Production Association is one of the biggest nuclear facilities in the Russian Federation, housing plutonium production reactors and a reprocessing plant. It was built by the USSR during the build up to the cold war. The Mayak plant did not comply with the safety regulations and dumped about 100 tons of highly radioactive waste into the nearby Lake Karachay.The city also witnessed one of the world's worst nuclear tragedies – The Kyshtym Disaster – which had ripped through the plant and released deadly radiation in 1957.