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
Nucleate boiling formula_6 is the Prandtl number of the liquid. The bubble Reynolds number, formula_7 is defined as, formula_8 Where formula_9 is the average mass velocity of the vapor leaving the surface and formula_10 is the liquid viscosity. Rohsenow has developed the first and most widely used correlation for nucleate boiling, <math>\frac{q}{A}= Nucleate boiling Nucleate boiling is a type of boiling that takes place when the surface temperature is hotter than the saturated fluid temperature by a certain amount but where the heat flux is below the critical heat flux. For water, as shown in the graph below, nucleate boiling occurs when