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
Boiling Springs, Pennsylvania year round. This is arguably the most intensely fished section of water in Pennsylvania when the White Mayfly hatches. Limestone bedrock streams are rich in minerals, which serve as the basis for the trout's food chain and contribute to healthy growth rates for trout. Boiling Springs and South Middleton Township, which are near the halfway point of the Appalachian Trail, were designated Pennsylvania's first Appalachian Trail Community. In 2010, the Appalachian Trail Conservancy started recognizing towns near the trail that are assets to hikers and the trail. As of 2012, Boiling Springs is one of 23 designated Appalachian Trail Communities.