Question

A nucleus decays by $ \beta^+ $ - emission followed by a $ \gamma $ -emission. If the atomic and mass numbers of the parent nucleus are $ Z $ and $ A $ respectively, the corresponding numbers for the daughter nucleus are respectively :

• A. $ Z − 1 $ and $ A − 1 $
• B. $ Z+1 $ and $ A $
• C. $ Z − 1 $ and $ A $
• D. $ Z+1 $ and $ A − 1 $

Answer 1

Answer: (C)

$\beta$ -rays are fast moving electrons.
When there is an excess of protons in the nucleus and it is not energetically possible to emit an $\alpha$ -particle, $\beta^{+}$ decay occurs. Resulting in reducing atomic numbers by $1 .$ New atomic number $=Z-1$, mass number $=A .$ Gamma ray emission occurs with $\beta^{\prime}$ emission. Since gamma rays have no charge or mass their emission doesnot change the chemical composition of the atom.
Hence, atomic number $=Z-1$, mass number $=A$