Question

The most common isotope of Uranium, ²³⁸U₉₂, radioactively decays into lead, ²⁰⁶Pb₈₂, y a means of a series of alpha and beta particle emissions. How many of each particle must be emitted.

A) 32 alphas, 10 betas 

B) 16 alphas, 16 betas 

C) 16 alphas, 8 betas

D) 8 alphas, 6 betas 

E) 4 alphas, 18 betas

Answer 1

The correct option is: (D) 8 alphas, 6 betas 

Explanation:

Beta particles do not change the atomic mass number since there is simply a conversion between nucleons, so the only way to reduce the mass number is by emitting alpha particles. The mass number goes down by 32 and each alpha particle reduces it by 4 so 8 alpha particles are needed. 8 alpha particles by themselves would also reduce the atomic # by 16, but it only ends up reduced by 10 so there are 6 protons needed. These 6 protons come from the beta decay where 6 neutrons turn into protons and release 6 beta particles.