Question

In both β⁻ and β⁺ decay processes, the mass number of a nucleus remains the same, whereas the atomic number Z increases by one in β⁻ decay and decreases by one in β⁺ decay. Explain giving reason.

Answer 1

In β⁻ decay, a β particle of zero mass and −1 charge is emitted. The decay process is shown below:

\[^{A}_{z}{X} \to\ ^{A}_{Z + 1}{Y} +\ ^{0}_{- 1}{\beta} + \nu\]

Since the mass of β⁻ particle is negligibly small, the mass number of the nucleus remains the same and the atomic number increases by 1 due to the loss of 1 negative charge.
Similarly, for a β+ decay, a β particle of negligibly small and +1 charge is emitted. The decay process is shown below:

\[^{A}_{z}{X} \to\ ^{A}_{Z + 1}{Y} + ^{0}_{+ 1}{\beta} + \nu\]

The mass number remains the same, but here, the atomic number decreases by 1 due to the loss of 1 positive charge.