A form of an element that has isotopic abundances that are different from the naturally occuring form. Compare with isotope and polymorph . Some elements occur in several distinct forms called allotropes.
Allotropes have different chemical and physical properties.
For example, graphite and diamond are allotropes of carbon. A particle that is commonly ejected from radioactive nuclei, consisting of two protons and two neutrons. Alpha particles are helium nuclei. A stream of alpha particles . Alpha rays rapidly dissipate their energy as they pass through materials, and are far less penetrating than beta particles and gamma rays .