Helium results from the fusion of four hydrogen nuclei to form one helium nucleus. This reaction also generates energy and is the source of power at the core of stars.
Constituting about 24 percent of the mass of the macrocosm, helium is the second lightest and second most common element in the universe, the first being hydrogen. Despite its abundance in the universe at large, helium is not common on Earth and makes up only about 0.00052 percent of the Earth's atmosphere.
Most helium on Earth results from radioactive decay that is created during the process of nuclear fission. Elements like uranium in the Earth's crust and upper mantle are primary helium sources. Approximately 78 percent of the world's helium comes from the United States.
Some researchers have raised concerns over the use of helium for frivolous reasons such as party balloons. There is a limit to Earth's helium supply, and the element is critical in research and to hospitals, which use helium in devices such as MRI scanners. The Rutherford Appleton Laboratory in the United Kingdom had to cancel several experiments in 2012 because the facility had run low on helium. This illustrates just how scarce helium can sometimes be.