DMI 261 RADIATION BIOLOGY and PROTECTION

UNIT 1 THE ATOM  Nucleus Protons Protons Neutrons Neutrons  Shells / orbits electrons electrons

Protons  Nucleon  + electrical charge  mass  Opposite charge of the electron

Neutrons  Nucleon  No charge – neutral  mass

Shells / Orbits  Electrons Exist in electron cloud Exist in electron cloud Arranged in precise orbits or energy levels Arranged in precise orbits or energy levels - electrical charge - electrical charge mass mass

Maximum electrons / shell  K = 2  L = 8  M = 18  N = 32  O = 50  P = 72  Q = 98

Binding energy of an atom  Holds electrons in orbit  Measured in electron volts (eV)  Inner electrons are tightly bound  Outer electrons are loosely bound and easily ionized

Valence shell  The outermost shell of loosely bound electrons.  # of electrons in valence shell determines the atom’s combining ability.

Ionization  Ionize – to remove electrons from an atom.  Occurs when an x-ray photon transfers its energy to an orbital electron and ejects it from its shell.  An ion pair is formed.

ION PAIR  + charged atom  free electron

Atomic Number  Number of protons in the nucleus  “Z” number  Written at the bottom of the chemical symbol

Atomic Mass  Sum of the protons and neutrons in the nucleus.  “A” number  Written at the top of the chemical symbol

Isotopes  Atoms that have the same atomic number but different mass number.  Atoms that have the same # of protons but a different # of neutrons.  Most elements have more than one stable isotope and some radioactive isotopes.

Medical Radioisotopes  Used in Nuclear Medicine Imaging  Man-made in particle accelerators called cyclotrons  Technetium 99m  Iodine 123  Xenon 133 gas