Alpha decay is another prevalent form of radioactive decay. In alpha decay, the nucleus emits an alpha particle, which is essentially a helium nucleus (\( \alpha \) or \( \mathrm{^{4}_{2}He} \) ). This form of decay has noticeable effects:
- The atomic number of the original element decreases by 2 as two protons are removed.
- The mass number decreases by 4 because the nucleus loses a total of four nucleons (two protons and two neutrons).
For example, in the alpha decay of bismuth-212: \[ \mathrm{^{212}_{83}Bi \rightarrow ^{208}_{81}Tl + ^{4}_{2}He} \] Bismuth (Bi), with atomic number 83, transitions to thallium (Tl), with atomic number 81, and the mass number drops from 212 to 208.