Helium is the second lightest element as well as the second most abundant element in the universe (hydrogen has the honor of holding the top spot in both cases). Helium is also the smallest of the noble gases, inert elements that do not readily form compounds with other elements due to their full electron shells. In its natural, stable state, helium has two protons (particles with positive charges) and two electrons (particles with negative charges). It also has 10 isotopes, some which are stable and some which are not. An isotope is a version of an element that has a differing number of neutrons (neutral particles), which increases the mass of the atom. Helium-3 (one neutron) and Helium-4 (two neutrons) are the most abundant and naturally occurring. But there are some “exotic” isotopes of helium that are coming to light as our knowledge of science continues to grow.
One of these exotic isotopes is helium-5. Helium-5, like all other helium isotopes, has two protons and two electrons. It differs from the others in the fact that it has three neutrons. It is one of the unstable isotopes, having a half-life of significantly less than a picosecond (a trillionth of a second). A half-life is the time it takes for half of the substance to decay. All of the exotic isotopes of helium have half-lives of less than a second, but helium-5 is the shortest-lived. Researchers continue to make these exotic isotopes from collisions in particles accelerators in the hopes that their strange nuclear structures may offer insights into the properties of neutrons.
Due to its very short existence, the properties and usefulness of helium-5 have not been readily established. Scientists do know that it is an intermediate product of the fusion reaction between deuterium and tritium. Intermediate products are made in one step of a multi-step reaction and used up in a later step, and obviously have some sort of importance or the reaction would proceed directly to the final product. Deuterium and tritium are isotopes of hydrogen, with deuterium having one neutron and tritium having two. When these two are fused, they briefly make helium-5 before it decays into the more stable isotope helium-4. The study of fusion reactions, which are the same as those that give the sun its power, is important in the hunt to find more natural sources of renewable energy. If nuclear reactions can produce cheap and safe energy for consumption, it could help solve the energy crisis that we continue to face. Will helium-5 be one of those keys? Only time and research will tell.