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| | A helium nucleus.
Helium ion with 2+ charge; an assembly of two protons and two neutrons.
A positively charged particle ejected spontaneously from the nuclei of some
radioactive elements. It is identical to a helium nucleus that has a mass
number of 4 and an electrostatic charge of +2. It has low penetrating power
and a short range (a few centimeters in air). The most energetic alpha
particle will generally fail to penetrate the dead layers of cells covering
the skin and can be easily stopped by a sheet of paper. Alpha particles are
hazardous when an alpha-emitting isotope is inside the body.
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