Q. 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 $A - 1$
Explanation
(c) 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$\beta^{+}$emission. Since, gamma rays have no charge or mass their emission does not change the chemical composition of the atom.
Hence atomic number$= \ Z - 1$,
mass number$\ = A\ $
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.