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Helium is the least water-soluble monatomic gas, [96] and one of the least water-soluble of any gas (CF 4, SF 6, and C 4 F 8 have lower mole fraction solubilities: 0.3802, 0.4394, and 0.2372 x 2 /10 −5, respectively, versus helium's 0.70797 x 2 /10 −5), [97] and helium's index of refraction is closer to unity than that of any other gas. [98]
Helium-2, 2 He, is extremely unstable. Its nucleus, a diproton, consists of two protons with no neutrons.According to theoretical calculations, it would be much more stable (but still β + decay to deuterium) if the strong force were 2% greater. [18]
Liquid helium is a physical state of helium at very low temperatures at standard atmospheric pressures.Liquid helium may show superfluidity.. At standard pressure, the chemical element helium exists in a liquid form only at the extremely low temperature of −269 °C (−452.20 °F; 4.15 K).
A helium atom is an atom of the chemical element helium. Helium is composed of two electrons bound by the electromagnetic force to a nucleus containing two protons along with two neutrons, depending on the isotope , held together by the strong force .
Disodium helide (Na 2 He) is a compound of helium and sodium that is stable at high pressures above 113 gigapascals (1,130,000 bar). Disodium helide was first predicted [5] using USPEX code and was first synthesised in 2016.
Within this liquid state, helium has two phases referred to as helium I and helium II. Helium I displays thermodynamic and hydrodynamic properties of classical fluids, along with quantum characteristics. However, below its lambda point of 2.17 K, helium transitions to He II and becomes a quantum superfluid with zero viscosity. [2]
Helium 3 is rare on Earth, primarily produced by the radioactive decay of tritium, but it does reside in abundance in the lunar regolith, deposited by billions of years of solar wind.
Helium-3 (3 He [1] [2] see also helion) is a light, ... Also, the microscopic properties of helium-3 cause it to have a higher zero-point energy than helium-4.