Asker: Bart, 16 years old
Answer
The half-life of Uranium-238 (the most abundant isotope on Earth) is just under 4.5 billion years. The Uranium was created during the explosion of a supernova (a large star), also about 4.5 billion years ago. The Earth was created from debris from that explosion.
Half-life means that if you have a number of U atoms, half of them will remain after a half-life. The other half has broken up into pieces, which is also called fission. Breaking into pieces produces other radioactive elements, such as radioactive iodine, and releases a few neutrons.
The only way to make the fission happen faster than ‘naturally’ is to start a chain reaction, breaking up a U atom, releasing neutrons that break up a few other U atoms, and so on. That is exactly what happens in a controlled manner in a nuclear reactor. The same principle can be used for some other radioactive elements (eg plutonium, americium, etc.): this is called ‘transmutation’.
Higher up I wrote “of course” in quotes. The reason is that there have been real natural nuclear reactors in nature, such as at Oklo in Gabon, where the concentration of U was so high two billion years ago that there have been spontaneous reactors in several places that have been active for several hundred thousand years. .
Frank Deconinck
Answered by
Professor Frank Deconinck
Medical applications of physics Nuclear energy and applications
Free University of Brussels
Pleinlaan 2 1050 Ixelles
http://www.vub.ac.be/
Pleinlaan 2 1050 Ixelles
http://www.vub.ac.be/
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