Another isotope capable of fissioning under neutron bombardment is uranium-233. It does not occur in nature, but was formed in the laboratory by Seaborg and others in 1942. It has a half-life of 162,000 years. It can be formed from naturally occurring thorium-232. Thorium-232 will absorb a neutron to become thorium-233. Then 2 beta particles are given off so that the thorium-233 becomes first protactinium-233 and then uranium-233. If a thorium shell surrounds a nuclear reactor, fissionable uranium-233 is formed within it and is easily separated from the thorium. In this way, thorium is also added to the list of earth’s potential nuclear fuels.[4] If all the uranium and thorium in the earth’s crust (including the thin scattering of those elements through granite, for instance) were available for use, we might get up to 100 times as much energy from it as from all the coal and oil on the planet. Unfortunately, it is very unlikely that we will ever be able to make use of all the uranium and thorium. It is widely and thinly spread through the crustal rocks and much of it could not be extracted without using up more energy than would be supplied by it once isolated. Another problem rests with the nature of the fission reaction. When the uranium-235 nucleus (or plutonium-239 or uranium-233) undergoes fission, it breaks up into any of a large number of middle-sized nuclei that are radioactive—much more intensely radioactive than the original fuel. (It was from among these “fission products” that isotopes of element 61 were first obtained in 1945. Coming from the nuclear fire, it reminded its discoverers of Prometheus, who stole fire from the sun in the Greek myths, and so it was called “promethium”.) The fission products still contain energy and some of them can be used in lightweight “nuclear batteries”. Such nuclear batteries were first built in 1954. Some batteries, using plutonium-238 rather than fission products, have been put to use in powering artificial satellites over long periods. Unfortunately, only a small proportion of the fission products can be put to profitable use. Most must be disposed of. They are dangerous because the radiations they give off are deadly and cannot be detected by the ordinary senses. They are very difficult to dispose of safely, and they must not be allowed to get into the environment, especially since some of them remain dangerous for decades or even centuries. [Illustration: _The Experimental Breeder Reactor No. 2 building complex in Idaho. The reactor is in the dome-shaped structure._] NUCLEAR FUSION The Energy of the Sun As it happens, though, nuclear fission is not the only route to useful nuclear energy.