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.