(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, $A=238$

$\therefore A=238-4\times 8=206$