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{{r|Helium}}

...[elementary charge]]. An &alpha;-particle is in fact the nucleus of the [[helium]]-4 [[isotope]], consisting of two [[proton]]s and two [[neutron]]s, thus h ...ption required </ref> in which it was explained that &alpha;-particles are helium atoms that have lost their negative charge. In 1908 it was not yet known th

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...ic and subatomic particles, such as [[electron]]s (&beta;-radiation) and [[helium]] nuclei (&alpha;-radiation), or of high-energy massless particles, [[photo ...e a (theoretical) [[rest mass]] of zero. The &alpha; and &beta; particles (helium nuclei and electrons) have rest mass not equal to zero; the same is true f

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...when the Earth first formed its atmosphere mostly contained hydrogen and [[helium]], but the gravity was not strong enough to hold onto these light gases and ...[[Jupiter]], [[Saturn]], [[Uranus]] and [[Neptune]] have more hydrogen and helium in their atmosphere. Being further out from the sun they received large amo

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