Atomic number - The number of protons in the nucleus of the atom. Since the protons are positively charged, enough negatively charged electrons are collected around the nucleus to neutralize or charge balance the atom. These protons and electrons give the atom its unique chemical nature.

Atomic mass - The sum of the weights of both the neutrons and the protons in the atom.

Electron - A small negatively charged particle that surrounds the nucleus with a mass about 1/1800 that of the proton . Beta particles are energetic electrons ejected from a radioactive nucleus.

Element - the most basic physical substance composed of all the same type of atoms. Each atom will have the same number of protons. The number of neutrons can differ.

Isotope - Atoms with the same number of protons, but differing in the number of neutrons present in the nucleus. Most elements have more than one isotope.

Neutron - An electrically neutral particle found in the nucleus with a mass almost that of the proton. In the fission process, neutrons are liberated.

Nucleus - The densely packed kernel of the atom containing protons and neutrons. The diameter of the nucleus is 100,000 to 200,000 smaller than the whole atom.

Photon - The smallest unit of light. The photon is often described as a electromagnetic wave or wave packet. Light photons from red to blue in the visible spectrum have increasing energy. X-rays and gamma rays are energetic photons with thousands to millions of times the energy of light photons.

Proton - An electrically positive particle found in the nucleus of the atom. Each proton is balanced by the charge of an electron surrounding the nucleus. The electrically neutral atom has the same number of negative electrons as positive protons.

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