H-bomb: Same as hydrogen bomb.
Heavy hydrogen: Same as deuterium.
Heavy water: Water with heavy hydrogen substituted for ordinary hydrogen.
Hydrogen bomb: A high-yield thermonuclear bomb.
Iodine¹³¹: A radioactive fission product with a half-life of 8 days. It emits an electron of average energy 0.2 million electron-volts and a gamma ray of energy 0.4 million electron-volts.
Ion: A charged atom or molecule. Ions are produced in abundance when energetic charged particles pass through matter.
Ionization: The process of removing electrons from neutral atoms or molecules. Neutrons and gamma rays as well as energetic charged particles are very effective in producing ionization.
Iridium¹⁹²: 75 day radioisotope. It emits an electron of average energy 0.2 million volts and a 0.3 million volt gamma ray.
Isotopes: Atoms whose nuclei have the same number of protons but a different number of neutrons. Such atoms have the same chemical behavior.
Kiloton: The amount of energy released by a thousand tons of TNT.