Known as the Trinity test, the plutonium bomb was detonated over the New Mexico desert, initiating a chain reaction that released 18.6 kilotons of power.
It marked the beginning of the Atomic Age.
Less than a month later, the US dropped two atomic bombs on the Japanese cities of Hiroshima and Nagasaki, killing more than 100,000 people instantly.
Thousands more died from their injuries, radiation sickness and cancer in the years that followed, bringing the toll closer to 200,000, according to the US Department of Energy’s history of the Manhattan Project.
To raise awareness of the effects of nuclear weapons testing and achieve a nuclear-weapons-free world, every year on August 29 the United Nations marks the International Day against Nuclear Tests.
Who has carried out nuclear tests?
According to the Arms Control Association, at least eight countries have carried out a total of 2,056 nuclear tests since 1945.
Of those, 507 have been atmospheric explosions, which spread radioactive materials through the atmosphere. In 1963, the Limited Test Ban Treaty led to a huge reduction in atmospheric explosions.
The United States has conducted just over half of all nuclear tests, with 1,030 tests between 1945 and 1992.
The Soviet Union carried out the second highest number of nuclear tests at 715 tests between 1949 and 1990. The USSR’s first nuclear test was on August 29, 1949. The test, codenamed RDS-1, was conducted at the Semipalatinsk test site in Kazakhstan.
According to the Preparatory Commission for the Comprehensive Nuclear Test-Ban Treaty Organization (CTBTO), the Soviet Union conducted 456 tests at the Semipalatinsk test site, with devastating consequences for the local population such as genetic defects and high cancer rates.
Kazakhstan closed the Semipalatinsk test site on August 29, 1991. Following this move, the UN established August 29 as the International Day against Nuclear Tests in 2009.
France has carried out 210 nuclear tests, while the United Kingdom and China have each carried out 45 tests.
India has carried out three nuclear tests, while Pakistan has carried out two.
North Korea is the most recent nation to carry out a nuclear test. In 2017, its sixth and most powerful bomb was detonated at the Punggye-ri nuclear test site. The underground explosion created a magnitude-6.3 tremor.
The largest nuclear explosion occurred in 1961, when the Soviet Union exploded the Tsar Bomba on Novaya Zemlya north of the Arctic Circle. The explosion’s yield was 50 megatonnes, 3,300 times more powerful than the nuclear bomb dropped on Hiroshima.
The largest nuclear test conducted by the US was the Castle Bravo test which took place on March 1, 1954, at Bikini Atoll in the Pacific Ocean. The explosion yielded 15 megatonnes, with a mushroom cloud of roughly 40km (25 miles).
The power of the nuclear test was miscalculated by scientists, and it resulted in radiation contamination that affected the inhabitants of the atolls. The nuclear fallout of the explosion is said to have spread over 18,130 square kilometres (7,000 square miles).
Where have nuclear tests been carried out?
Nuclear weapons have been tested all around the world.
On February 13, 1960, France carried out its first nuclear test, codenamed Gerboise Bleue, over the Sahara desert in Algeria – which it was occupying at the time.
Other nuclear test sites include a number in the US states of Nevada, New Mexico, Colorado and Mississippi.
Tests have been carried out in Australia, China, India, Kazakhstan, North Korea, Russia and Pakistan as well as on French Polynesia, Kiritimati, the Marshall Islands, Prince Edward Island in the Indian Ocean and in the open sea in the eastern Pacific and south Atlantic oceans.
In 1979, a US Vela satellite detected an atmospheric nuclear explosion over Prince Edward Island in the Indian Ocean. Many believe this was an undeclared joint nuclear test carried out by South Africa and Israel.
What are the effects of different levels of radiation?
Nuclear testing has immediate and long-term effects caused by radiation and radioactive fallout. Increased rates of cancer have been associated with nuclear testing, with studies showing that thyroid cancer is linked to radionuclides.
After a nuclear test, large areas of land remain radioactive for decades.
The health effects of different levels of radiation vary from nausea and vomiting to death within days.
The UK conducted a series of nuclear tests in the South Pacific Ocean between November 1957 and September 1958. A survey conducted in 1999 by the British Nuclear Test Veterans Association found that the impact of the tests on 2,500 veterans who had been present showed that more than 200 had skeletal abnormalities and 30 percent of the men had died, mostly in their fifties.
Radiation exposure is measured in roentgen equivalent man (rem) – a unit of radiation measurement applied to humans resulting from exposure to one or many types of ionising radiation.
The infographic below shows the effects of radiation on the human body.
