Question

How many alpha and beta particles are emitted when Uranium nucleus ₉U²³⁸ decays to Lead If ₈₂Pb²⁰⁶ ?

Answer 1

On emission of one alpha particle, the mass number decreases by 4. With the emission of an alpha particle, the atomic number decreases by 2 but when a β-particle is emitted, the atomic number increases by 1.

\[\ce{_92U^238->[-α]_90X^234}\], where X represents the new nucleus

\[\ce{_90X^234->[-β]_91X^234->[-α]_89^230->[-β]_90^230->[-α]_88^226->[-α]_89^226->[-α]_87^222->[-α]_88^222->[-α]_86^218->[-β]_87^218->[-α]_85^214->[-β]_86^214->[-α]_84^210->[-α]_82Pb^206}\]

No. of α-particles emitted = 8.
No. of β-particles emitted = 6.