# Chapter 2 Fundamentals of Physics & Chapter 3 The Atom by ECW97R

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```									    Chapter 3 Fundamentals of
Physics & Chapter 4 The Atom
• Physics is the study of the interaction of
matter & energy.
• Physicist strive for simplicity. There are
three base quantities.
– Mass
– Length
– Time.
Base Quantities Support
Derived Quantities
• From the base
quantities, derived
quantities are formed.
are special quantities.
–   Exposure
–   Dose
–   Dose equivalent
–   Activity
Units of Measure
• Every measurement has two parts: a
magnitude and a unit.
• Four systems of units
– MKS (meters, kilograms, seconds)
– CGS ( centimeters, grams, seconds)
– British (Foot, Pound, Seconds)
– International (SI) (Meter, Kilogram, Seconds)
Standards of Mass and Time
• Mass: The kilogram is the unit for Mass.
Mass is not weight.
• For weight: The Newton or British Pound
are used.
• Time: Time is measured in seconds
Systems of Units
• The pound is actually a unit of force but is
related to mass.
• The SI has four additional base units.
There are special derived units and
special units for derived quantities &
special quantities.
Quantities
•   British           •   SI
•   Exposure          •   C/kg   Air Kerma (Gya)
•   Dose              •   J/kg   Gray (Gyt)
•   Dose Equivalent   •   J/kg   Seivert (Sv)
•   Activity          •   s-1     Becquerel (Bq)
Direction of Motion
• Mechanics deals with the motion of
objects.
• Motion of an object is described by the use
of two terms:
– Velocity or speed or how fast the object is
moving.
– Acceleration or the rate of change of
velocity.
• Velocity of light c= 3 x 108m/s
Velocity or Speed
• Velocity is how fast an object is moving or
the rate of change of position in time. The
metric measure is kilometers per hour or
meters per second.
• V= Distance / Time
• Average velocity is determined by adding
the initial velocity and final velocity and
dividing by 2.
Acceleration
• Acceleration is the rate of change of
velocity. It is measured in m/s2.
• Acceleration is velocity divided by time or
distance divided twice by time
• If velocity is constant, the acceleration
would be zero.
Newton’s Laws of Motion
• Newton’s First Law: A body will remain at
rest or continue moving with a constant
velocity in a straight line unless acted on
by an external force. The Law of Inertia
Newton’s Laws of Motion
• Newton’s second law define force: The
force (F) acting on an object with
acceleration (a) is equal to the mass (m)
multiplied by the acceleration. Force is
mass times acceleration.
• SI unit is Newton
• CGS unit is dyne. (1N=103 dyne)
• F=ma
Newton’s Laws of Motion
• Newton’s Third Law: To every action
there is an equal and opposite reaction.
Weight WT = mg
• Weight (WT) is a force on a body caused
by gravity. This rate is called the
acceleration of gravity (g)
• The value for earth are:
– SI g= 9.8 m/s2
– CGS g= 980 cm/s2
– British g= 32 ft/s2
Momentum p = mv
• Momentum is represented by p
• Momentum is the product of mass and
velocity.
• The greater the velocity of an object, the
more momentum the object possesses.
• The conservation of momentum law states
the total momentum before any interaction
is equal to the total momentum after the
interaction.
Work = fd
• Work done on an object is the force
applied times the distance over which it is
applied.
• The SI unit is joule (j)
• The CGS unit is erg
• An object held motionless has no work
according to the physics term.
Power P=Work/t
• Power is the rate of doing work.
• The SI term for power is watt (W) or
Joules/ second.
• The British term is horsepower (hp)
• 1 hp= 746 w
• 1000 W= 1 kilowatt (kW)
Energy
• Energy is the ability to do work. Energy
may be transformed from one form to
another but it cannot be created or
destroyed. The units for energy and work
are the same.
• To make x-ray, electrical energy is
converted heat and x-rays in the x-ray
tube.
Mechanical Energy
• There are two types of mechanical energy.
– Kinetic Energy (KE) or energy in motion
• KE = 1/2 mv2
• Kinetic energy is dependent upon the mass of the
object and the square of the velocity.
– Potential Energy (PE) or stored energy of
position or configuration.
• PE= mgh where h is the height above the earth’s
surface.
Heat
• Heat is a form of energy important to
radiology. Excessive heat will damage x-
ray tubes.
• Heat is the amount of kinetic energy of the
random disordered motion of molecules.
The unit for heat is calorie.
Heat
• 1 calorie equals the amount of heat
needed to raise the temperature of 1 g of
water 1 degree C.
• Heat is transferred three ways.
– Conduction
– Convection
– Thermal reaction
Heat
• Conduction is the transfer of heat by
molecular motion.
• Convection is the mechanical transfer of
hot molecules in a gas or liquid from one
place to another.
Heat
• Thermal reaction is the transfer of heat
through space that depends upon the
temperature of the object.
• X-ray tubes use thermal reaction for
cooling.
• Thermal radiation is the transfer of heat
by the emission of infrared radiation. It is
that red glow that come off very hot
objects.
Temperature units
• There are three scales of temperature
– Fahrenheit (°F) Tf= 9/5Tc -32
– Celsius (°C) Tc= 5/9Tf +32
– Kelvin (K) Tk = Tc +273
Chapter 3 The Atom
• One of sciences most pronounced and
continuing investigation has been
determining the structure of matter.
• The Greek used the term atom to describe
the smallest part of the four substances of
matter. They were air, fire water earth.
• This persisted until 1808.
The Atom
• Today there are over 100 elements: 92 are
naturally occurring and over 15 have been
artificially produced
• In 1808, John Dalton showed that
elements could be classified according to
integral values of atomic mass.
The Atom through the Ages
The Elements
• In the middle of the 19th century, a
Russian scholar Dmitri Mendeleev was
credited with showing that if the elements
were arranged in the order of increasing
atomic mass, a periodic repetition of
similar chemical properties occurred. His
work resulted in the Periodic Table of the
Elements
The Atom
• In the late 1890’s J.J. Thompson theorized
that the atom was like a plumb pudding
where the plumbs represent negatively
charged electron and the pudding was a
shapeless mass of positive electrification.
• In 1911 Earnest Rutherford disproved
Thompson’s model of the atom.
The Atom
• The Rutherford atom has a small positively
charged nucleus and a cloud of negatively
charged electrons.
• In 1913 Neils Bohr improved upon
Rutherford’s description of the atom as a
miniature solar system. His method still
works though quantum mechanics model
is more accurate.
The Molecule
• Atoms of various elements combine to
form molecules. A measurable quantity of
one type of molecules is called a chemical
compound. Molecules make structures.
Fundamental Particles
• The atom as
described by Bohr
consists of orbiting
negatively charges
electrons and a
nucleus containing
protons and neutrons
quarks bound
together by gluons.
Fundamental Particles
• The fundamental
particles of the atoms
are electrons, protons
and neutrons.
• Atomic particles are
so small, they are
expressed in atomic
mass units.
• 1 amu = 1/12 the
mass of a carbon 12
atom.
Atomic Structure
• The nucleus of the atom contains 99.98% of the
mass of a element. The nucleus contains
nucleons called protons and neutrons. The
neutron has no charge while the protons carry a
positive charge.
• The electrons carry a negative charge and are
arranged in shell. The arrangement of shells
determine how the atom reacts chemically or
how it combines with other atoms to form
molecules.
Atomic Structure
• The number of protons determines the chemical
element.
• Atoms with a different number of neutrons are
called isotopes.
• The electrons are arranged in shells given codes
K, L,M,N,.. To represent the electron binding
energies. K being the innermost shell.
• Electrons closer to the nucleus have higher
binding energies.
• Electrons farther away from the nucleus have
greater potential energy.
Atomic Structure
• Atoms are electrically neutral. Because the
number of electrons and protons are equal.
• The positive charge of the nucleus provided a
binding force for the atom.
• If the atom has an extra electron or an electron
is removed, it is said to be ionized.
• Ionized atoms are no longer electrically neutral.
• Ionization is possible only with addition or loss of
electrons. A change in protons would change
the element. A change in neutrons would not
cause ionization.
Electron Arrangement
• Physicist call the shell number n the
principle quantum number.
• The maximum number of electrons that
can exist in each shell increases with the
distance of the shell from the nucleus.
• The number can be calculated by the
expression 2n2 where n is the shell
number.
Electron Arrangement
• The number of electrons in the outermost
shell of an atom is equal to its group in the
periodic table.
• The number of electrons in the outermost
shell determines the valence of a atom.
Electron Arrangement
• No outer shell can contain more than 8
electrons.
• All atoms that have one electron in the outer
shell fall in group one of the periodic table and
two electrons fall in group two.
• This orderly progression is interrupted in the 4th
outer shell, one is added to the inner shell.
These are called transitional elements.
Electron Arrangement
• Shell notation of the electron arrangement of an
atoms not only identifies the relative distance of
an electron from the nucleus but indicates the
relative binding energy by which the electron is
bound to the nucleus.
• The centripetal force or the force of attraction
of the negative charge of the electron and the
positive charge of the nucleus balances the
centrifugal force or the force of the electron
velocity to keep the electrons in precise orbits.
Electron Binding Energy
• The strength of the attachment of the
electron to the nucleus is called the
electron binding energy or Eb.
• The electron closer to the nucleus is more
tightly bound than the outer shell electron.
• Not all K-shell electrons are bound with
the same binding energy. The greater the
total number of electrons, the more tightly
each is bound.
Electron Binding Energy
• The larger and more complex atoms have higher
Eb than smaller atoms because of the greater
number of protons.
• It take more energy to ionize these larger atoms.
• Carbon is one of the important components of
human tissue. As with other tissue atoms, Eb is
approximately 10 eV. Yet is take about 34eV to
ionize tissue atoms. The 34 eV is called the
ionization potential. The difference 24 eV
causes multiple excitations resulting in heat.
Atomic Nomenclature
• Often elements are identified by an
alphabetic abbreviation called the atomic
symbol.
• The chemical properties are determined
by the number and arrangement of
electrons. In the neutral atom, the number
of electrons and protons are the same.
This is called the atomic number or Z.
Atomic Nomenclature
• The number of protons and number of
neutrons in the nucleus of the atoms is
called the atomic mass number or A.
• The atomic mass number and the precise
mass number are not equal. The actual
precise atomic number (amu) is
determined by actual measurement.
The Tungsten Atom
Isotopes
• Atoms that have the same atomic number
but different atomic mass numbers are
isotopes.
• Barium has an atomic number of 56. Its
atomic mass number is 138 and is based
upon the average of the seven isotopes of
barium. Each has a different atomic mass
but reacts chemically the same.
Isobars
• Isobars are atoms that have different
numbers of protons and neutrons but the
same number of nucleons.
• Isobaric radioactive transitions from parent
atom to daughter atoms result in the
release of a beta particle or positron. The
parent atom and the daughter atoms are
of different elements.
Isotones & Isomers
• Atoms with the same number of neutrons
but different number of protons are
isotones.
• Isomers have the same atomic number
and the same atomic mass number.
Characteristics of Various Nuclear
Arrangements
Arrangement Atomic     Atomic Mass   Neutron
Number     Number        Number
Isotope    Same        Different     Different

Isobar     Different   Same          Different

Isotone    Different   Different     Same

Isomer     Same        Same          Same
Combinations of Atoms
• Atoms of various elements may combine
to form structures called molecules.
• A compound is any quantity of one type
of molecule.
• Some atoms have nuclei that contain
excess energy or an unstable nucleus. To
reach stability, the nucleus
spontaneously emits particles and energy
to transform itself into another atom. This
• These atoms are called radionuclides. Any
nuclear arrangement is called a nuclide
while only those at under go decay are
• When an atom contains too many or too
few neutrons, it will under go radioactive
decay.
• There are only two sources of naturally
– They were formed when the earth was
formed.
– They are exposed to cosmic radiation in the
upper atmosphere.
been identified for almost every element.
• There are many ways
by which
decay to reach
stability but only two
are of particular
importance.
– Beta emission
– Alpha emission
• During Beta emission , an electron like
particle is ejected from the nucleus with
considerable kinetic energy. The neutron
is transformed into a proton.
• Most elements are capable of Beta
emission.
• Alpha emission is much more violent. An
alpha particle consists of two neutrons and
two protons.
• The atom loses two units of positive
charge and four of mass.
• It must be a very unstable to under go
alpha emission.
• Some radioisotopes are pure beta emitters
and some are pure alpha emitters but
most emit gamma rays simultaneously
with the particles.
• Radioactive materials disintegrate at an
ever decreasing rate. The half life is the
time it takes for the quantity of radioactivity
to be reduced by 50%.
• The concept of half life is essential to
radiology. It is used daily in nuclear
medicine.
• It’s parallel in x-ray terminology is Half
Value layer
• There are two types of ionizing radiation.
• Alpha particles
• Beta particles
• X-rays
• Gamma Rays
Alpha Particles
• Alpha particles have atomic mass of 4 with
a positive charge. Because of it’s mass, it
easily transfers it’s kinetic energy to the
orbital electrons resulting in ionization.
Alpha particles are emitted by the nuclei of
heavy elements.
• The average alpha particle has 4 to 7
MeV.
Beta Particles
• Beta particles have no atomic mass and
carry a negative charge. The only
difference between an electron and a beta
particle is it’s origin.
• It has 0 to 7 MeV Kinetic energy and can
penetrate 2 cm of tissue.
• Gamma rays and x-rays are often called
photons. A photon is the smallest unit of
• Photons have no mass or charge and
travel at the speed of light.
• Like beta particles, the difference between
gamma rays and x-rays is their point of
origin.