Alpha particles come from the nucleus of a radioactive atom. They consist of 2 protons and 2 neutrons; hence have a 2+ charge. A few centimeters of air will stop them. Alpha radiation consists of ...

^{4}\textrm{He}\) When a radioactive atom emits an alpha particle the mass number decreases by four and the atomic number drops by two. Here is the equation for the alpha decay of radon-219 into ...