Card Set Information

2013-12-04 16:21:08

Show Answers:

  1. what are the basic parts of a cathode assembly
    • filament
    • focusing cup
    • associated filament wires
  2. what is the purpose of the focusing cup
    what element is made out of
    • its purpose is to narrow the thermionic cloud as it is driven to the anode
    • nickel
  3. what is the composition and charge of the focusing cup
    • it is a shallow depression composed of nickel that focuses the electrons toward one another in convergence pattern because of it s geometry
    • it has a low negative charge
  4. what is a biased focusing cup
    what does it do to the electrons
    where is it often used
    it is the cup that maintains at a more negative voltage than the filament

    causes the the electron stream to become narrower as it goes towards the anode

  5. what is the space charge effect
    happens when more and more electrons build up in the area of the filament and their negative charges begin to oppose the emission of additional electrons
  6. What is the maximum mA range of the space charge effect?
  7. at what temperature does thermionic emission occur
    2200 degrees celsius no less or it will not happen
  8. what is thermionic emission
    process by which electrons are liberated or boiled off the filament
  9. why is tungsten used for the filament
    • has high atomic number
    • high melting point
    • difficult to vaporize
  10. what is the melting point of tungsten
    3370 celsius
  11. what is the line focus principle
    why is it used
    • is a principle in which the desgin of anode target are is angled
    • it used to reduce the effective focal spot, whuch permits the best resolution of detail
  12. according to the line focus principle, when the target angle is less than 45 degrees, the effective focal spot is always ____ than the actual focal spot
    smaller than
  13. why does a smaller filament give you better detail
    it has less divergence of the xray photons which produces fine detail images
  14. what is the actual focal spot and the effective focal spot
    • the physical area of the focal track that is impacted
    • the area of the focal spot that is projected out of the tube and down to the object being radio graphed
  15. what is the anode heel effect
    because of the geometry of the angle target area the radiation is intensifies on the cathode side
  16. why does the anode heel effect happen
    becuase photons emitted toward the anode end of the tube are more likely to be absorbed by the target material than those emitted toward the cathode end
  17. how many more photons are on the cathode end of the tube
    • 20% more on cathode
    • 255 less on anode
  18. when is the anode heel effect most noticeable
    on a large film but at a short distance
  19. how do we take advantage of the anode heel efffect
    we position the patient so that the cathode end is over the thicker denser part and anode over a less dense part
  20. what is the anode warmup procedure
    • process of warming the tube using moderate kvp moderate mas and long exposure
    • 1 sec exposure followed by 2 more 2 second exposures
  21. normal use of the rotating anode will eventually vaporize sufficient targe tfocal track material to ________
    to roughen or pit the target area
  22. what is the function of the stator
    what is it composed of
    where is it located
    • it turns the rotor
    • composed of induction motor magnets
    • it is only structure located outside of the glass envelope
  23. what is the function of the rotor
    location of rotor
    what is it composed
    • it turns the anode disk
    • it is located withing the stator
    • composed of a hollow copper cylinder cuff and is attached to a molybdenum shaft
  24. what is the purpose of ball bearings and where are they located
    • they are used as lubricants between the cylinder and the anode shaft to facilitate the turning of the anode
    • they are located witihn the rotor
  25. how fast do common rotating anodes revolve
    how fast do the high speed anodes revolve
    • 3200-3600rpm
    • 10000-12000 rpm
  26. what is the function of the glass envelope
    what is it made out of
    • to maintain a high vacuum
    • heat resistant pyrex glass
  27. what is the function of the protective housing
    what is made out of
    • controls leakage and scatter radiation
    • isolates high voltage and provides a means of control the tube for the radiographer
    • steel
  28. what is leakage radiation
    how much leakage is permitted
    • it is the radiation that escapes all areas of the steel housig except at the window
    • not exceed 100mR/hr at 1 meter
  29. what permits the electrons to flow from cathode to anode without encountering the gas atoms of air
    presence of a vacuum
  30. anode target surface area is composed of what element
  31. normal use of the rotating the anode will eventually vaporize sufficient target focal track material to ______
    roughen or pit the target area
  32. what is off focus radiation
    when does it occur
    • radiation composed of photons not produced at the focal spot
    • when high voltage electrons striking the target produce scattered electrons from photons or other areas of the tube
  33. how does off focus radiation effect the radiographic image
    how much of the primary beam is considered off focus radiation
    • they cause a ghosting effect
    • 25-30% of primary beam
  34. what is the purpose of a tube rating chart
    they provide a guide regarding the max tech factor combinations that can be used without overloading the tube
  35. when is a set of tech factors considered safe when using a tube rating chart
    when the amount of radiation is either on or below the curve on the graph
  36. what is the purpose of the cooling curve
    what units are they measured in
    • this chart permits the calcualtion of the time necesary for the anode/housing to cool enough for additional exposures to be made
    • heat units
  37. what is the formula for heat units
    what are the rectification constants
    • kvp x ma x time x rectification constant
    • single phase 1.00
    • 3 phase 6 pulse 1.35
    • 3 phase 12 pulse 1.41
    • high frequency 1.45
  38. what are the reccomendations for extending tube life
    • warm up the tube
    • depress rotor and exposure switches at the same time
    • use low ma when possible
    • do not make repeat exposures
    • do not use tube if you can hear loud ball bearings
  39. what is an incident electron
    it is the electron that is coming in from the filament
  40. what percentage of interactions at the target reslt in the production of xray photons
  41. describe a brems interaction
    An incident electron reacts with the force field of the nucleus, causing the electron to slow down, diverting the electron’s course; the electron loses energy and changes direction; the energy lost in the "braking" is a bremsstrahlung photon.
  42. what determines the strength of the xray photon created during a Brems interaction
    the amount of energy lost as the incident electron bends around the nucleus
  43. describe a characteristic interaction
    these interactions may occur only when the incident electron interacts with an inner shell electron and gets ejected

    The reaction of electrons dropping into the holes created during a characteristic interaction until there is only a hole in the outer shell
  44. what determines the strength of the xray photon created during a characteristic interaction
    is this predictable
    • the amt of energy lost when an electron jumps from an outer shell to an inner shell
    • energy is predictable
  45. what is the characteristic cascade
    happens after an outer shell electron has dropped to fill the hole another electron will drop to the fil lthe hole it left and so on untl only the outermost shell is missing an electrons
  46. what is the k shell binding energy of tungsten
  47. at what kvp will characteristic interaction begin to occur
    greater than 70 KVP
  48. what is the characteristic peak
    it is a burst or spike on the emission graph that occurs when the k shell reach their effective energy of over 70 kvp
  49. within the diagnostic range, what type of interaction procedures produce most photons
    brems interaction
  50. what is the average energy of an xray beam
    30-40% or primary beam
  51. how is the emission spectrum changed when the mA time or mAs has changed
    increase in quantity (number) of electrons change (increase or decrease depending on the change)
  52. how is the emission spectrum affected when the kVp (quality and energy) is changed
    results in change in the number of photons as well as the amplitude
  53. what type of radiation produces the most ionizations per unit length of tissue
    alpha particles
  54. what interaction produces photons that are completely predictable
    • characteristic
    • brems
  55. define somatic and genetic
    • somatic pertains to the skin and body (cataracts, skin erythema, cancer)
    • genetic deals with our DNA effects offsprin
  56. list examples of natural radiation
    • cosmic radiaition (space)
    • terrestrial radiaition (ground)
    • naturally present radionuclides (internal and external)
  57. what is the largest source of natural radiation
  58. what is largest source of man made radiaition
    nuclear medicine and CT scan
  59. list some sources of man made radiation
    • xrays
    • radiopharmaceuticals
    • air trvel
    • consumer products
    • nucleur fuel
    • fallouts (bombs)
  60. what is the average effective dose equivalent for a member of the US population in mrem
    6.25 mSv or 625 mrem
  61. what is the unit of exposure
    R or roentgen (measures radiation in air)
  62. what is the unit of absorbed dose
  63. what is the unit of equivalent dose
  64. what is the quality factor
    type of radiation weigh factor
  65. what is the formmula for determining equivalent dose
    rad x QF = REM
  66. state several types of dosimeters employed tp detect and measure radiation
    • geiger mueller survey instruments
    • scintillation detection devices
    • ionization chamber instruments
  67. what field survey instrument is commonly employed for the measurement of the primary and secondary radiation beam for purposes of evaluation of equipment performances
    ionization chamber instruments
  68. which particle is least penetrating and which causes the least ionization per unit length
    alpha and xray
  69. what effect becomes evident in the indivudal exposed
  70. which dosimeter is measure in mR or R
    pocket dosimeters
  71. which dosimeter contains aluminum dioxide
    osl dosimeter
  72. which dosimeters contains lithium fluoride crystals
    tlds (thermoluminescent dosimeters)
  73. which dosimeters have filters used to determine radiation quality
  74. which dosimeter is most sensitive to radiation
  75. where should badges be worn? One issued?Two issued? During fluoro?
    • typically between chest and waist
    • one = on the waist until you get to fluoro and then move it to outside of the thyroid shield
    • two = on collar and at the waist
    • during fluoro one outside thyroid shield the other under the lead apron at waist level
  76. what can adversely affect film badges and TLD's
    • environmental factors
    • heat humidity pressure
    • prolonged exposure to light
  77. what is a control badge
  78. what are the occupational exposures for the following:
    cumulative, lens of the eye, skin hands and feet
    • annual 5 rem
    • cumulative age x 1
    • lens of eye 15 rem
    • skin hands and feet 50rem
  79. what are the public & student exposures for the following:
    cumulative, lens of the eye, skin hands and feet
    • whole body .1 rem
    • lens of eye 1.5rem
    • skin hands and feet 5 rem
  80. what are the embryo/fetus exposures for the following:
    monthly and whole term
    • monthly .05 rem
    • 9 month whole term .5rem
  81. what does alara
    as low as reasonably achievable
  82. what are the principles of personnel exposure reduction
    time distance shielding
  83. what cells are radiosensitive
    • wbcs, rbcs, thyroid cells, spermegonia, oogenia cells, skin cells
    • because they are constantly dividing to give us more and more
    • we give blood away, our body undergoes mitosis to create more blood
  84. what is the most radioresistant cell in the body
    • cells of CNS b/c they do not regenerate if they are damaged they can repair but we cant make more nerve cells
    • spinal cord
    • muscle cells
  85. describe a primary barrier
    how much lead is it
    • its is the areas struck by the primary beam the floor and the wall bucky
    • lined with 1/16 pb/Eq
  86. describe a secondary barrier
    how much lead
    • it is the areas struck by scatter and leakage radiation
    • 1/32'' pb/eq
    • all other walls ceiling control booth
  87. what is the lead equivalency for protective aprons and gloves
    • lead aprons min of .5mm pb/eq
    • gloves .25mm pb/eq
  88. what technique factors should be used to minimize patient dose
    • high kvp and low mas
    • more penetration low absorption
  89. what principles should be applied to minimize patient dose
    shielding collimation and communication
  90. what is NRC regulation 10CFR19.12
    requires that instructions to women assigned to radiation exposure areas must include explanation of the right to declare or not declare pregnancy status as well as requiring that all info in NRC regulatory guide 8.13 be discussed
  91. when is a women most radiosensitive
    8-15 weeks post conception
  92. why is it no longer common practice to assign declared pregnant women to areas where exposure is likely to be lower
    because it is unfair to other workers
  93. what does filtration eliminate
    low energy long wavelength photons
  94. what is the purpose of filtration
    harden the beam and get rid of low wavelength photons
  95. what is the hvl
    the amount of absorbing material that will reduce the intensity of the primary beam by one half its original value
  96. what is added filtration
    list examples
    what is its al/Eq
    • is located outside of the tube and protective housing and before the IR
    • collimator mirror collimator box anything that is added in crease the half value
    • 1mm al/eq
  97. what is inherent filtration
    list examples
    what is the al/eq measurement
    • filtration built in the tube things you cant change in it
    • thickness of glass tube, oil that surrounds the tube, the glass window of the housing
    • .5-1mm al/eq
  98. what is standard filtering material
    what measurement is it expressed in
    • aluminum
    • mm al/eq
  99. what is a compound filter
    • uses two or more filters/materials the complement one another in their absorbing materials
    • it is made so that each layer absorbs the characteristic photons from the previous layer
    • each layer breaks it down further and further until absorbption
  100. what is a compensating filter
    list examples
    • used to even out the unequal subject densities
    • wedge filter - even out densities of the feet
    • trough filter - even out densities in the chest
    • boomerang filter - used for shoulders
  101. what is total filtration
    it is the added filtration plus the inherent filtration
  102. when filtration is increased, what must be done to technical factors to maintain the density
    increase of mas
  103. what is the reccommended filtration levels for equipment operating below 50, 50-70, and above 70 kvp
    • 50 kvp - .5mm/al
    • 50-70 1.5mm/al
    • 70 kvp - 2.5mm/al (max)
  104. what is the inverse square law (xray intensity and distance)
    if you double distance you get 4 x less ore 4 more radiation from the source
  105. what is the unit of measurement used to express occupational exposure for film and TLD readings
  106. what causes pitting or many small surface melts on the anodes focal track
    repeated, frequent overloading
  107. what key factor will not affect patient dose
    focal spot size
  108. what two things serve to increase the average energy of the xray beam
    an increase of kvp and increase in added filtration
  109. how does filtration affect the primary beam
    filtration increases the avg energy of the primary beam
  110. the size of the focal spot in use is determined by what?
    mA selected
  111. for a given exam dose to which anatomic structure will be the greatest
    skin not the gonads
  112. man made sources of radiaition include
    • nuclear fallout
    • medical and dental xray productions
    • building materials that emit radiaition (like bricks)