RADIATION THEORY
A more detailed discussion of radiological theory can be found in
the Troxler Nuclear Gauge Safety Training Program manual,
provided at the Troxler Safety Class.
ATOMIC STRUCTURE
All matter is made up of atoms. For example, water has two atoms
of hydrogen (H) and one atom of oxygen (O), which in chemical
notation is written H
2
O.
An atom is made up of a dense nucleus, consisting of positively
charged protons and uncharged neutrons, surrounded by a cloud of
negatively charged electrons. Under normal circumstances, the
number of electrons in an atom equals the number of protons. The
number of protons in the atom is called the atomic number (Z). A
chemical element consists of all atoms having the same atomic
number.
The number of protons plus neutrons in the nucleus is called the
atomic mass (A). Atoms of a given chemical element can exist in
slightly different variants called isotopes that have different atomic
masses. For example, carbon-12 (C-12) is non-radioactive and
carbon-14 (C-14) is radioactive. Isotopes that are radioactive are
termed radioisotopes or radionuclides.
Figure A–1 depicts a helium atom consisting of two protons and two
neutrons in the nucleus and two orbiting electrons.
ELECTRONS
NEUTRON
PROTON
Figure A–1. Diagram of an Atom
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