Will give medal! A radioactive nucleus decays to yield a bismuth-211 nucleus and an alpha particle. What was the identity of the original nucleus?

Question

jfraser · Answer

just like "normal" chemical reactions, nuclear reactions still obey laws of conservation. The TOTAL number of protons in a nuclear reaction must be conserved, and the TOTAL mass number must be conserved. If you know what the products mass and atomic numbers are, you know what the original nucleus must have originally contained

jfraser · Answer

$$^{238}_{92}U \rightarrow \space ^4_2 \alpha + \space  ^{234}_{90}Th$$