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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. Unlike for hydrogen , a closed-form solution to the Schrödinger equation for the helium atom has not been found.
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 ...
The term helion is a portmanteau of helium and ion, and in practice refers specifically to the nucleus of the helium-3 isotope, consisting of two protons and one neutron. The nucleus of the other (and far more common) stable isotope of helium, helium-4, consisting of two protons and two neutrons, is called an alpha particle or an alpha for short.
Because they are identical to helium nuclei, they are also sometimes written as He 2+ or 4 2 He 2+ indicating a helium ion with a +2 charge (missing its two electrons). Once the ion gains electrons from its environment, the alpha particle becomes a normal (electrically neutral) helium atom 4 2 He. Alpha particles have a net spin of zero.
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.
An important property of helium-3, which distinguishes it from the more common helium-4, is that its nucleus is a fermion since it contains an odd number of spin 1 ⁄ 2 particles. Helium-4 nuclei are bosons, containing an even number of spin 1 ⁄ 2 particles. This is a direct result of the addition rules for quantized angular momentum.
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or "decays" into a different atomic nucleus, with a mass number that is reduced by four and an atomic number that is reduced by two.
When there are many helium atoms around, alkali metal ions can attract shells of helium atoms. Clusters can be formed from absorbing metal into helium droplets. The doped droplets are ionised with high speed electrons. For sodium clusters appear with the formula Na + He n with n from 1 to 26. Na + He is the most common, but Na + He 2 is very ...