Half-Life Of Uranium-235 is 700 Million Years, Then Why Are People In Hiroshima Still Alive?


Uranium is not a problem in this case, as its radioactivity is very low. This is due to the long half-life. How much uranium will decay per second with a half-life of 700 million years? This is a very insignificant figure.

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Half-Life Of Uranium-235 is 700 Million Years
Half-Life Of Uranium-235 is 700 Million Years

During the explosion of a nuclear bomb, hundreds and thousands of isotopes are formed. Most of them exist for no more than a few seconds, and some are very much smaller. But at least 4 of the resulting isotopes are long-living, and they emit enough radiation to be considered dangerous.

This group of the long-living includes isotopes of iodine, strontium, cesium, and carbon. They exist for from several weeks to several millennia.

The half-life of iodine-131 is 8 days. In just 50 days, the amount of iodine-131 in Hiroshima reached 1% of the initial amount. Cesium has a half-life of 30 years. Therefore, it is dangerous in the future. Hiroshima cesium radiation is still about 16% of the original. Strontium has a half-life of 28 years. Today, its radiation has decreased to about 12% of the original.

The half-life of carbon-14 is 5,700 years. Every second, it produces small radiation. Therefore, it presents a real danger only at a sufficiently high concentration.

Bombs in Hiroshima and Nagasaki were detonated about 500 meters above the ground. This was done to maximize damage. The vast majority of radioactive isotopes scattered with the wind. The radiation from the explosions was not recorded after a few years.

The above means that the radiation hazard from nuclear disasters, even as serious as Chernobyl, will be practically negligible in a few centuries. Naturally, it will not disappear completely, but it will be extremely small. After 300 years, for example, only 1/1000 strontium of the original volume will remain.

Today, approximately 2 million people live in Hiroshima and Nagasaki.


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