an alpha particle has a mass number of
Alpha decay 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 an atom with a mass number that is reduced by four and an atomic number that is reduced by two. An alpha particle is identical to the nucleus of a helium-4 atom, which consists of two protons and two neutrons. It has a charge of +2e and a mass of 4u. For example, uranium-238 decays to form thorium-234. Alpha particles have a charge +2, but as a nuclear equation describes a nuclear reaction without considering the electrons – a convention that does not imply that the nuclei necessarily occur in neutral atoms – the charge is not usually shown.
Coulomb It is equivalent to the charge of approximately 7018624200000000000♠6.242×1018 (6995103600000000000♠1.036×10−5 mol) protons, and −1 C is equivalent to the charge of approximately 7018624200000000000♠6.242×1018 electrons.
Density The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is
Atom Ubiquitousness and stability of atoms relies on their binding energy, which means that an atom has a lower energy than an unbound system of the nucleus and electrons. Where the temperature is much higher than ionization potential, the matter exists in the form of plasma—a gas of positively charged ions (possibly, bare nuclei) and electrons. When the temperature drops below the ionization potential, atoms become statistically favorable. Atoms (complete with bound electrons) became to dominate over charged particles 380,000 years after the Big Bang—an epoch called recombination, when the expanding Universe cooled enough to allow electrons to become attached to nuclei.[114]