The residue of radioactive contamination which still endures has its origin in the nuclear tests conducted by the Great Powers during the period 1945-1980 as part of the Cold War and the Arms race. The H bombs or hydrogen fusion bombs, although more powerful had less fall out than atomic bombs to start with.
The effects of the radioactivity dispersal have decreased over time. Initially, at the peak of the trials in the 1960s, the annual doses reached 0,100 mSv per year. Today the annual dose is set at 0.005 mSv per year in European countries like Belgium, far from the test sites.
This exposure is low compared to the average 1 mSv received through medical examinations, but contributes to important part of artificial radioactive residue outside the medical field
It is greater than that, released by nuclear power plants and the residual radioactivity of Chernobyl, outside the most affected areas.By far the biggest part of radioactivity coming from powerful explosions are found in the stratosphere, where it remains for around 7 years, before settling three quarters in the Northern hemisphere and one quarter in the Southern hemisphere.
The total collective dose involved as a result of the atmospheric tests has been estimated at 30 Million"man-sievert". Shared over 5 billion individuals, this represents the equivalent to two and a half years exposure to natural radioactivity, namely around 6.0 mSv per person.
In terms of activity, the main radioelements subsisting are : tritium (spread in abundance by the hydrogen bombs), carbon-14, caesium-137 and strontium-90. In terms of effective doses, the main contributor is carbon -14 (70%), followed by caesium-137 (13%). The contamination due to tritium and carbon-14, radioelements produced also by cosmic rays, are of little concern .
Because of its half-life of 5730 years, the carbon-14 released by nuclear tests will vanish extremely slowly ... and may disrupt the future radiocarbon-14 dating performed by our descendents. One estimates to 0.22 EBq (1 etabecquerel = 1 billion of billions of becquerels) the amount of radioacarbon produced as a result of atmospheric testing. This amount, compared to the 11.5 EBq accumulated as a result of cosmic rays, corresponds to an excess of about 2%. Most of this carbon ends up in the ocean, 1.6% going in the troposphere.
Limited attention is paid to tritium, which have a very low radiotoxicity and vanishes with an half-life of 12 years. More worrying are cesium-137 and strontium-90 which have an half-life of around last 30 years.
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