Question

During alpha emission of a radioactive element, how do the following change?

1. Atomic number of the radioactive element.
2. Mass number of the radioactive element.

Answer 1

During alpha emission, the nucleus ejects an alpha particle, which is a helium nucleus $${}_{2}^{4}\mathrm{He}$$. Therefore:

(i) Atomic number decreases by 2.

(ii) Mass number decreases by 4.

\[ {}_{Z}\mathrm{X}^{A} \longrightarrow {}_{Z - 2}\mathrm{X}_{1}^{A - 4} + {}_{2}\mathrm{He}^{4} \]

Example:

\[ {}_{92}\mathrm{U}^{238} \longrightarrow {}_{90}\mathrm{Th}^{234} + {}_{2}\mathrm{He}^{4} \]