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Q.
A decay chain of the nucleus $\_{92}^{238}U$ involves eight $\alpha $ -decays and six $\beta $ -decays. The final nucleus at the end of the process will be
NTA AbhyasNTA Abhyas 2022
Solution:
(i) When $\alpha $ -particle is emitted from a radioactive nucleus then atomic number decreases by $2$ and atomic mass decreases by $4$ .
(ii) When $\beta $ -particle emitted from a radioactive nucleus then atomic number is increased by $1$ and atomic mass unaffected.
Here, atomic number $\left(Z\right)=92$
After emitting $8 \, \alpha $ -particles and $6\beta $ -particles,
$Z=92-2\times 8+6=82$
and atomic mass, $A=238$
$\therefore A=238-4\times 8=206$