Answer:
It is a nuclear reaction as Thorium here undergoes beta decay which is nuclear reaction
Step-by-step explanation:
Beta decay occurs when an unstable nucleus emits a beta particle and energy. A beta particle is either an electron or a positron. Positron can be considered as an anti-electron as it has a positive charge unlike electrons. When the beta particle is an electron, the decay is called beta-minus decay. When the beta particle is a positron, the decay is called beta-plus decay. Beta-minus decay occurs when a nucleus has too many neutrons relative to protons, and beta-plus decay occurs when a nucleus has too few neutrons relative to protons. Thorium undergoes beta minus decay and produces Actinium and an electron.