The core of the atom, where most of its mass and all of its positive charge is concentrated. Except for hydrogen, it consists of protons and neutrons. Any species of atom that exists for a measurable length of time. A nuclide can be distinguished by its atomic weight, atomic number, and energy state. A quantity of electromagnetic energy.
Photons have momentum but no mass or electrical charge.
Proton One of the basic particles which makes up an atom. The basic unit of an absorbed dose of ionizing radiation. One rad is equal to the absorption of 100 ergs of radiation energy per gram of matter. Radioactive dating A technique for estimating the age of an object by measuring the amounts of various radioisotopes in it. Radioactive waste Materials which are radioactive and for which there is no further use.