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MED 107- MEDICAL PHYSICS II > 8. X-RAYS: INTERACTIONS OF HIGH ENERGY ELECTRONS WITH MATTER > Flashcards

8. X-RAYS: INTERACTIONS OF HIGH ENERGY ELECTRONS WITH MATTER Flashcards

1
Q
  1. Which kinds of electrons are accelerated towards the anode?
A
  • electrons that are released from the filament of the X-
    Ray Tube
  • they are released by Thermionic Emission
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2
Q
  1. How is Thermionic Emission accomplished?
A
  • it is accomplished using a potential difference
  • this potential difference is found between the cathode
    and the anode
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3
Q
  1. What is another term for: “Potential Difference”?
A
  • Voltage
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4
Q
  1. What determines the number of electrons released in each exposure?
A
  • the selected mA (current)
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5
Q
  1. How do we find out the total number of X-Rays produced during an exposure?
A
  • this is set by the milliamperes per second (mAs)
  • this is the product of exposure time (TE)
    in seconds
    AND the electron current (mA)
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6
Q
  1. What determines the Kinetic Energy acquired by the electrons?
A
  • the selected kV
  • this is the Voltage
    (Potential Difference)
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7
Q
  1. What happens to the electrons as they reach the anode?
A
  • the interact with the atoms of the anode
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8
Q
  1. What are the 2 Parameters of an X-Ray beam?
A
  1. QUALITY OF THE X-RAY BEAM
    - this is determined by the energy of the electrons
    - the kV x p
  2. QUANTITY OF THE X-RAY BEAMS
    • this is the amount
    • it is the number of electrons
    • the mAs
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9
Q

9.What are the 3 types of interactions that will occur between the electrons and the atoms of the Anode?

A
  1. Incoming electrons will interact with the outer-shell
    electrons of the target atoms
  2. Incoming electrons will interact with the inner-shell
    electrons of the target atoms
  3. Incoming electrons will interact with the nuclei of the
    target atoms
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10
Q
  1. How many interactions do incoming electrons usually undertake with the target atoms?
A
  • around 1000 interactions
  • then they give up all their kinetic energy
  • these interactions will occur within 0.5mm of the
    surface of the target
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11
Q
  1. What is Tungsten’s Atomic Number?
A
  • 74
  • this means that there are 74 electrons in each atom of
    the target material
  • all these electrons are available for interactions
  • most of these electrons are found on the outer orbitals
    of each of the Tungsten atoms

NB:
- the incoming electrons will require relatively small
amounts of energy to interact with the shell-bound
electrons

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12
Q
  1. What happens when incoming electrons interact with the electrons in Tungsten atoms?
A
  • small amounts of energy are released as
    electromagnetic radiations
  • the energy amounts are too small to produce X-Rays
  • this means that virtually all the energy is release as
    heat
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13
Q
  1. What results in the electromagnetic radiations being released during interactions between electrons?
A
  • Electrostatic Repulsion
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14
Q
  1. What percentage of energy produced at the target of the X-Ray tube occurs in the form of heat?
A
  • 99%
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15
Q
  1. Which 2 interactive processes between incoming electrons and target atoms produce X-Rays?
A
  1. Characteristic Radiation
  2. Bremsstrahlung Radiation
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16
Q
  1. Provide the descriptions for parts of this diagram numbered 1-6.
A
  1. INCOMING FAST ELECTRONS
    • these collide with the electron from the inner orbital
      of the atom
  2. EJECTED ELECTRON
  3. VACANT ELECTRON ORBITAL POSITION
  4. ELECTRON FROM ANOTHER ORBITAL FILLS THE
    VACANCY
    • this is usually from a higher orbital
  5. ENERGY IS RELEASED AS A CHARACTERISTIC X-RAY
  6. THE FURTHER AWAY FROM THE NUCLEUS THE
    ORBITAL IS:
    • the higher the orbital energy will be
17
Q
  1. What kinds of shells are K and L Orbital Shells?
A
  • inner shells
18
Q
  1. What do the two orbital shells in Tungsten allow for?
A
  • the ejection of a electron
  • this leads to the emission of a photon
  • this photon has Electromagnetic Radiation
19
Q
  1. When can these Electromagnetic Radiated Photons be perceived as X-Rays in nature?
A
  • when they have the sufficient energy to escape from
    the X-Ray tube
20
Q
  1. What are 2 types of Characteristic Radiation reactions?
A
  1. EXCITATION
  2. IONISATION
21
Q
  1. What is Excitation?
A
  • this is when sufficient energy is given to the orbital
    bound electron
  • this electron will now be raised to the next orbital
22
Q
  1. What is Ionisation?
A
  • this is when the binding energy of an orbital electron is
    overcome
  • the electron is released from the atom
23
Q
  1. What can be said about the removal of the electron from its orbital shell during Excitation?
A
  • the electron has only been removed temporarily
  • the electron remains within the structure of the atom
  • the electron ultimately returns back to its original
    position
24
Q
  1. What does Excitation result in?
A
  • it results in a photon being given out
  • this photon has the same amount of energy as the
    energy gained by the electron when it raised itself to a
    different orbital shell
25
Q
  1. What is the released electron known as when it comes to Ionisation?
A
  • it is known as a Delta Ray
  • it carries kinetic energy with it
  • this energy is donated during the interaction
26
Q
  1. What will the Delta Ray do during Ionisation?
A
  • it will interact with other atoms
  • this will continue until it has lost all of its acquired
    energy
27
Q
  1. When does Ionisation occur?
A
  • it only occurs if the kinetic energy that carried by the
    incoming electron
    is equal to or greater
    than the specific binding energy of the orbital bound
    electron
28
Q
  1. What can be said about the electron energies when it comes to Tungsten?
A
  • the K-Orbital Binding energy is 69.5 keV
  • the L-Orbital Binding energy is 10.2 keV
29
Q
  1. What happens when the K-Shell Electron is ionised?
A
  • it will leave the atom with a vacancy in the K-shell
    orbital
  • this kind of vacancy cannot be sustained in nature

IMMEDIATELY:
-an electron from an outer orbital shell will drop into
the K-Shell

30
Q
  1. What happens once the outer orbital electron has dropped into the K-Shell Orbital vacancy?
A
  • an X-Ray will be released
  • its energy value will be equal to:
    the energy value of the donating shell MINUS
    the energy value of the receiving shell
31
Q
  1. What happens if an electron moves from the L-Shell to the K-Shell?
A
  • this is known as a K-Alpha emission
32
Q
  1. What happens if an electron moves from the M-Shell to the K-Shell?
A
  • this is known as a K-Betta Emission
33
Q
  1. What will the removal of an inner shell electron always result in?
A
  • it will always lead to the production of X-Rays
  • these X-Rays fall into well defined energy bands
  • these energy bands are characteristic for each atom
  • these radiations are characteristic of the material in
    which they are produced

MED 107- MEDICAL PHYSICS II (108 decks)

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