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.
• For radiology there
  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.
         SI units for Radiologic
               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
  which are made of
  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
  period. Instead of adding another electron to the
  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.
              Radioactivity
• 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
  process is called radioactive disintegration
  or radioactive decay.
             Radioactivity
• These atoms are called radionuclides. Any
  nuclear arrangement is called a nuclide
  while only those at under go decay are
  radionuclides.
• When an atom contains too many or too
  few neutrons, it will under go radioactive
  decay.
              Radioactivity
• There are only two sources of naturally
  occurring radioisotopes.
  – They were formed when the earth was
    formed.
  – They are exposed to cosmic radiation in the
    upper atmosphere.
• Artificially produced radioisotopes have
  been identified for almost every element.
               Radioactivity
• There are many ways
  by which
  radioisotopes can
  decay to reach
  stability but only two
  are of particular
  importance.
  – Beta emission
  – Alpha emission
             Radioactivity
• 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.
             Radioactivity
• 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.
              Radioactivity
• 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%.
              Radioactivity
• 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
                   Radiation
• There are two types of ionizing radiation.
  – Particulate radiation
     • Alpha particles
     • Beta particles
  – Electromagnetic Radiation
     • 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.
    Electromagnetic Radiation
• Gamma rays and x-rays are often called
  photons. A photon is the smallest unit of
  electromagnetic radiation.
• 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.
    Electromagnetic Radiation
• Gamma rays are emitted from the nucleus
  of a radioisotope. They have 0-5 MeV and
  can penetrate 30 cm of tissue
• X-rays are produced outside the nucleus
  in the electron shells. They have 0-100
  MeV and can penetrate 30 cm of tissue.
  The End of Lecture

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