Helium-3

Natural helium is obtained by extraction from deposits in the ground. It is a harmless inert gas, safe to breathe. School children breathing helium from birthday balloons delight in the changes to their voices caused by helium’s low density. Because nitrogen at high pressure can dissolve into tissues and produce a narcotic or anesthetic effect, deep sea divers breathe mixtures of helium and oxygen to benefit from the low solubility of helium in tissues.

Natural helium, however, is not magnetic. Its nucleus contains four nucleons, each pair canceling one another’s magnetism. Helium-3 is chemically identical to natural helium (Helium-4), but its nucleus is magnetic because it has only one neutron. Helium-3 is stable (not radioactive) and similarly harmless.

Very little Helium-3 is found in nature. Extraction of this Helium-3 would be prohibitively expensive. There is, however, a fairly abundant source of Helium-3 gas. Modern nuclear weapon triggers require radioactive tritium, a heavy isotope of hydrogen with three nucleons. Tritium has a half-life of 12.3 years, emitting a weak beta particle and, one by one, converting to Helium-3 atoms. This gas is collected, purified, and sold to scientists. The world’s supply of affordable Helium-3 is, therefore, limited to the amounts made available by continuous production of tritium for maintaining the world’s nuclear stockpile.