Isotopes of helium a thousand times lower than helium-4 (2.17 K). This difference is explained by quantum statistics, since helium-3 atoms are fermions, while helium-4 atoms are bosons, which condense to a superfluid more easily. The most common isotope, , is produced on Earth by alpha decay of heavier radioactive elements; the alpha particles that emerge are fully ionized nuclei. is an unusually stable nucleus because its nucleons are arranged into complete shells. It was also formed in enormous quantities during Big Bang nucleosynthesis. Terrestrial helium consists almost exclusively (99.99986%) of this isotope. Its boiling point of 4.2 K is the lowest of
The Elements (song) the song "Tchaikovsky and Other Russians", written by Ira Gershwin, which listed fifty Russian composers in a similar manner. "The Elements" differs from the "Major-General's Song" in that: "The Elements" has been featured in popular culture many times. In the episode "Ex-File" of "NCIS", Timothy McGee and Abby Sciuto hum the song, which forms a key clue in their case. In "The Big Bang Theory" episode "The Pants Alternative", a drunk Sheldon Cooper starts to sing the song during his acceptance of an award from his university. In the 2006 episode of "Gilmore Girls" called "The Real Paul Anka", Luke