1 Principles of Imaging Science I (RAD119) Physics Fundamentals & Atomic Structure Goals • Understand the structure of matter and the fundamentals of electromagnetic radiation. • Understand the concept of x-ray production, how x-rays interact with matter, the quantity and quality of the x-ray beam, and demonstration of anatomic structures in the radiographic image (radiograph) An Art and a Science • Radiography as art • Scientific method • Natural science o Physical science: non-living matter • Physics o Biological science: living matter • Anatomy and Physiology
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Principles of Imaging Science I (RAD119)
Physics Fundamentals &
Atomic Structure
Goals • Understand the structure of matter and the
fundamentals of electromagnetic radiation.
• Understand the concept of x-ray production, how x-rays interact with matter, the quantity and
quality of the x-ray beam, and demonstration of
anatomic structures in the radiographic image (radiograph)
An Art and a Science
• Radiography as art
• Scientific method
• Natural science
o Physical science: non-living matter
• Physics
o Biological science: living matter
• Anatomy and Physiology
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Matter and Energy
• Physics studies relationships between matter
and energy
• Matter o Mass and occupies space
• Energy is force used to do work
Matter • Matter
• Anything that occupies space, has shape or form, and has mass
• States of matter: Solid, liquid, gas
• Mass • Amount or quantity of matter in an object.
• Does not change with a change in the form
• Does not change with gravitational force
• Air has mass, but much less than a rock that has the same volume because the particles of matter in air are
more widely spaced.
• Fundamental Unit - Atom • Composed of smaller units protons,
neutrons, and electrons
Atomic Theory
• Basic building blocks of matter
• Atom is unique and characteristic of a
certain type of matter
oHydrogen atom is different from an atom
of Barium or Calcium
• Atoms cannot be seen o Scientists theorized about its structure and function based
on experimentation
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Atomic Structure
• Nucleus
• Small, dense center
• Contains nucleons protons and
neutrons
• Electrons
• Orbit nucleus
Bohr Atom • Basic structure of atoms is comparable to
our solar system
• An atom is mostly empty space – the space between the electrons and the nucleus is like the space between the earth and sun
• Atom is comprised of a small, dense, positive nucleus and negative electrons revolving in orbit around the nucleus
Bohr Atom
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Basic Atomic Particles
• Proton
• Positive charge
• Represents the Atomic Z#
• Distinguishes elements by number of protons
in the nucleus
• Change the Z#, change the element!
Basic Atomic Particles • Neutron
• Neutral charge
• Stability of nucleus
• Serve in the role in radioactive atoms (isotopes)
• Electron
• Negative charge
• Electrical stability maintained through equal
number of protons and electrons
Atomic Mass Unit (amu) • Unit used to measure atomic mass.
• It is not a metric unit, based on the standard of the carbon-12 atom.
• The equivalent mass in kilograms notes the small size of an atomic mass unit
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Electrons • Electrons (-) charge
• Subatomic particle
• Small quantity of mass
• Located outside nucleus in orbital shells
• Stable atoms have equal electrons as protons
• Electron shells • Ordered from the first shell (K) to
the last shell (Q)
Electron Shells • Represent the energy levels
• Maximum number of electrons in each shell based upon 2n2
• K shell: Shell #1 = 2 electrons (innermost)
• L shell: Shell #2 = 8 electrons (2)(2)2
• M shell: Shell #3 = 18 electrons (2)(3)2
• Q shell: Shell # 7 = 98 electrons (2)(7)2
• A maximum of 8 electrons may comprise the outermost shell of any atom (valence shell)
Electron Shell Maximum
Factoid: The largest naturally occurring atom, uranium, has a total of 92 electrons in its
seven shells. Even in this atom, shells 5, 6, and 7 are not completely filled.
Shell
Number
Principle
Quantum #
Shell Symbol Number of
Electrons
1 K 2
2 L 8
3 M 18
4 N 32
5 O 50
6 P 72
7 Q 98
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Forces • Nuclear Binding Energy
• Holds protons and neutrons together in the nucleus
• Sum of the strong nuclear forces that attract
and pull the protons and neutrons together in the nucleus
• Measure of the amount of energy needed to
“split the atom” • If a particle shot at the atom strikes the nucleus with
the energy equal to the nucleus's binding energy, the atom could break up or "split."
Forces Centripetal force
Maintains electron in orbit preventing it from flying away from the nucleus
“Center seeking force” Balances the force created by the electron velocity
Forces
Centrifugal force
Maintains electron at a distance from the nucleus while moving around the nucleus
“Out from center force”
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Forces • Electron Binding Energy (BE)
• Maintains electrons in their shells
• Dependent upon:
• Proximity to nucleus
• Higher BE closer to nucleus
• Total # electrons in the atom
• Higher BE in larger atoms
• Most of the BE comes from the force of attraction between the electrons and
protons
Electron Binding Energy (Eb)
• Energy needed to eject
electron from atom
TUNGSTEN
(Eb)Comparison
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Electron Binding Energy
CHARGE & IONS
• Neutral atoms: equal # of electrons and
protons
• Balanced or stable
• If an electron is added or removed the atom is no longer neutral: it becomes electrically charged.
• Negative ion - An atom with an extra electron
• Positive ion - - An atom that has one fewer electrons than protons