Q.Calculate the energy in MeV released in the nuclear reaction
174-77-Ir → 170-75-Re + 4-2-He
Atomic masses : Ir = 173.97 u, Re = 169.96 u and He = 4.0026 u
(Ans. 6.89 MeV)

Radioelements decay in three ways. Alpha decay is the emission of an alpha particle (a helium-4 nucleus, 4-2-He, charge +2, mass 4u): $^{A}_{Z}X \rightarrow\ ^{A-4}_{Z-2}Y + 4$-$2$-$He$, dropping the mass number by 4 and the atomic number by 2, so the daughter sits two places to the LEFT of the parent in the periodic table. Beta decay is the emission of a high-speed electron: $^{A}_{Z}X \rightarrow\ ^{A}_{Z+1}Y + 0$-$(-1)$-$e$, leaving the mass number unchanged but raising the atomic number by 1, so the daughter sits one place to the RIGHT of the parent. Gamma decay/emission is the release of high-energy electromagnetic radiation, almost always accompanying an alpha or beta decay, because th …