Solved Sample Paper 1 — Question 13

(a) When a radioactive uranium nucleus $_{92}^{238}\text{U}$ emits an α particle, a new nucleus thorium $_{90}^{234}\text{Th}$ is formed and the change is represented as follows —

$^{238}_{92}\text{U} \longrightarrow \space ^{234}_{90}\text{Th} + \space ^{4}_{2}\text{He}$

When thorium $_{90}^{234}\text{Th}$ isotope decays by a β-emission to an isotope of protactinium (Pa), the change is represented as follows —

$^{234}_{90}\text{Th} \longrightarrow \space ^{234}_{91}\text{Pa} + \space ^{\enspace 0}_{-1}\text{e}$