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Helium is found in large amounts in minerals of uranium and thorium, including uraninite and its varieties cleveite and pitchblende, [20] [137] carnotite and monazite (a group name; "monazite" usually refers to monazite-(Ce)), [138] [139] because they emit alpha particles (helium nuclei, He 2+) to which electrons immediately combine as soon as ...
Terrestrial helium consists almost exclusively (all but ~2ppm) [16] of 4 He. 4 He's boiling point of 4.2 K is the lowest of all known substances except 3 He. When cooled further to 2.17 K, it becomes a unique superfluid with zero viscosity. It solidifies only at pressures above 25 atmospheres, where it melts at 0.95 K.
The helium atom. Depicted are the nucleus (pink) and the electron cloud distribution (black). The nucleus (upper right) in helium-4 is in reality spherically symmetric and closely resembles the electron cloud, although for more complicated nuclei this is not always the case. Helium-4 (4 He) is a stable isotope of the element helium.
Helium is the most common element in the universe after hydrogen, with a mass fraction of about 24%. Most of the helium in the universe was formed during Big Bang nucleosynthesis, but the amount of helium is steadily increasing due to the fusion of hydrogen in stellar nucleosynthesis (and, to a very slight degree, the alpha decay of heavy ...
Helium is inert - it does not react with other substances or combust - and its atomic number is 2, making it the second lightest element after hydrogen. Rockets need to achieve specific speeds and ...
Helium is the smallest and the lightest noble gas and one of the most unreactive elements, so it was commonly considered that helium compounds cannot exist at all, or at least under normal conditions. [1] Helium's first ionization energy of 24.57 eV is the highest of any element. [2]
They fuse helium until the core is largely carbon and oxygen. The most massive stars become supergiants when they leave the main sequence and quickly start helium fusion as they become red supergiants. After the helium is exhausted in the core of a star, helium fusion will continue in a shell around the carbon–oxygen core. [20] [24]
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