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After five years of additional experimental work, Rutherford and Hans Geiger determined that "the alpha particle, after it has lost its positive charge, is a Helium atom". [7] [8] [9]: 61 Alpha radiation consists of particles equivalent to doubly-ionized helium nuclei (He 2+) which can gain electrons from passing through matter. This mechanism ...
Original – A diagram of a helium atom, showing the disparate sizes of the nucleus and electron cloud EDIT 1 – Red border and unencyclopedic pink dot removed. Reason Striking image illustrating the huge size difference between nuclei and electron clouds. Top image for four articles, including Atom Articles in which this image appears
The most common isotope, helium-4, is produced on Earth by alpha decay of heavier radioactive elements; the alpha particles that emerge are fully ionized helium-4 nuclei. Helium-4 is an unusually stable nucleus because its nucleons are arranged into complete shells. It was also formed in enormous quantities during Big Bang nucleosynthesis. [113]
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-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. At low temperatures (about 2.17 K), helium-4 undergoes a phase transition : A fraction of it enters a superfluid phase that can be roughly understood as a type of Bose–Einstein condensate .
The symbol is α or α 2+. Because they are identical to helium nuclei, they are also called He 2+ or 4 2 He 2+ indicating helium with a +2 charge (missing its two electrons). If the ion gains electrons from its environment, the α particle can be written as a normal (electrically neutral) helium atom 4 2 He.
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.
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus). The parent nucleus transforms or "decays" into a daughter product, with a mass number that is reduced by four and an atomic number that is reduced by two.