For example, a helium atom has an atomic mass of 4, but an atomic number (or positive charge) of 2. Since electrons have almost no mass, it seemed that something besides the protons in the nucleus ...

It is not the same as a helium atom as it does not contain any electrons but it is written with the same chemical nomenclature as a helium atom: \(_{2}^{4}\textrm{He}\) When a radioactive atom ...