Download Unit 1 Atom

DMI 261
RADIATION BIOLOGY
and PROTECTION
UNIT 1 THE ATOM

Nucleus



Protons
Neutrons
Shells / orbits

electrons
Protons

Nucleon
 + electrical charge
 1.00728 mass
 Opposite charge of
the electron
Neutrons

Nucleon
 No charge – neutral
 1.00867 mass
Shells / Orbits

Electrons




Exist in electron cloud
Arranged in precise
orbits or energy levels
- electrical charge
.000549 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