Radioactive elements give out alpha particles when they go through a kind of radioactive decay , known as alpha decay . Thus , alpha particles may be loosely used as a term when referring to stellar helium nuclei reactions ( for example the alpha processes ) , and even when they occur as components of cosmic rays . However , helium nuclei produced by particle accelerators ( cyclotrons , synchrotrons , and the like ) are less likely to be referred to as `` alpha particles '' because the high energies produced by these sources highlights the striking difference in behavior of their particles from the classical alpha particles produced ( and originally defined ) by the process of radioactive alpha decay .