Nuclear charge number is the number of protons in the nucleus of an atom.

See also Mass Number, Ordinal Number.

Fissile isotopes such as 233U, 235U or 239Pu get exposed to a thermal neutron beam. The resulting nuclear chain reaction is controlled by moderators such as graphite, Beryllium or heavy water.
For example Mo-99, source for Tc-99m, is produced by fission of highly enriched uranium (HEU) in a few reactors around the world (monitored and controlled by The International Atomic Energy Agency).

Stable elements get activated by neutrons.

A nucleon is a proton or a neutron - part of the nucleus.

The nucleus is the positively charged center of an atom and contains most of the mass. Except for 1H, the atom core consists of a combination of the subatomic particles protons and neutrons.