Atomic bombs legacy

A legacy of the cold war

Two and a half years of natural radioactivity ...
. The nuclear atmospheric tests have dispersed huge quantities of radioactive elements, as has been shown by the estimates of the total activities of the main radioactive elements released. For reason of radioactive decline, the contaminations (in red) which still subsists 40 years after the end of these trials concerns tritium, carbon-14, strontium-90 and caesium-137. It is considered that humanity has been exposed to the equivalent of two and a half years of natural radioactivity as a result of these tests. (NB: the unity used for these very strong activities is the “etabecquerel”).

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.

Cesium in Europe beforeChernobyl
Legacies of the Cold War, the main radioactive contaminations remaining 40 years after the cessation of atmospheric nuclear tests are due to cesium-137 and to a lesser extent, strontium-90, two radioactive nuclei with half-lives of about thirty years. The map shows the distribution of Cesium-137deposits in Europe, just before the Chernobyl accident in 1986. Ground contamination was around a kilobecquerel per square meter. On that date the contamination was divided by about two from the years1950-60.
Atlas of Chernobyl

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.

Cesium in Europe after Chernobyl
In 1986, the activity of the cesium-137 released by the Chernobyl accident added to the residue of the impact of atmospheric nuclear tests. The map shows contamination about 1000 times higher near Chernobyl compared to western Europe because of distance. Globally the amount of Chernobyl releases totaled about three times the residual activity in 1986 of the nuclear tests.

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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