Nuclear reactions can involve either fusion or fission. Fusion is the joining of two lighter nuclei to form a heavier nucleus and releases energy. Fission is the splitting of a heavy nucleus into two lighter nuclei and also releases energy. Controlled fission in a nuclear reactor can be used for energy production, while uncontrolled fission in a nuclear weapon can cause a devastating explosion.

6. NUCLEAR
REACTIONS
FUSION
REACTION
FISSION
REACTION

9. NUCLEAR
FISSION
CONTROLLED
NUCLEAR
REACTOR
UNCONTROLLED
NUCLEAR
WEAPON

19. Lighter Nuclei
Lighter Nuclei Heavier Nuclei
Energy
Free Neutron
Fusion