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)

Key Idea: $\beta -$ 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 p4 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 Note: During ${\beta }^{+}$ decay, a positron (a particle with the same mass as an electron but. With positive charge) and a neutrino are released.