Question

What kind of change takes place in a nucleus when a  β - particle is emitted? Express it by an equation. State whether

1. atomic number and
2. mass number are conserved in a radioactive β - decay?

Answer 1

On emitting a β particle, the number of nucleons in the nucleus (i.e. protons and neutrons) remains same, but the number of neutrons is decreased by one and the number of protons is increased by one.

If a radioactive nucleus P with mass number A and atomic number Z emits a beta particle to form a daughter nucleus Q with mass number A and atomic number Z+1, then the change can be represented as follows:

\[\ce{\underset{Parent nucleus}{^A_Z P}   ->[β particle]} \] \[\ce{\underset{Daughter nucleus}{{^A_{z+1} Q}}} +  \underset{\ce{(Beta-particle)}}{{^0_{-1} e}}\] 

1. Atomic number 'Z' is not conserved. It is increased by 1.
2. Mass number A is conserved.