Geiger counters, photographic plates, cloud and bubble chambers are all used to detect or observe radiation. Rutherford discovered the positive nucleus using his famous gold-foil experiment. Fusion requires that hydrogen be combined to make helium. Fission requires that a neutron causes uranium to be split into middle size atoms and produce extra neutrons. Radioactive half-lives can not be changed by heat or pressure.
Nuclear forces are strong and short ranged.
Special thanks to Physics teacher Jim Davidson for creating this list.