where is cathode located
in tube housing, inside envelope
is the cathode on the negative or positive side
negative
where is the vacuum located
between anode and cathode
What are the 4 parts of the cathode?
filament circuit and filament, focusing cup, and associated wiring
what does the cathode produce?
thermionic cloud, a group of elecs that have been boiled off and sit infront of the filament and focuses electron stream towards anode
what selection is the cathode used in
kVp
what is the role of the filament circuit
supplies pwr to filament
what does mAs determine for the cathode
how much pwr will be supplied to filament
the amount of mAs used is determined by….
size of body part
what is the filament
smal coiled wires made of thoriated tungsten.
it is heated to alloed for thermionic emission.
why is thoriated tungsten used in the filamen
tung- has high melting point
thor- increases the # of elecs that will be boiled off so we get a better image
what is thermionic emission
the elcs that get boiled off
what does the focusing cup do
helps direct elecs to the anode
what is supplied to the filament and how
the current, by the circuit.
amt of current supplied depends on mA selected and is normally between 100-800 mA
what causes the release of elecs from the filament ? how many are released?
the resistance of the filament causes ot to heat and release elecs, this happens when we half depress button.
the amt released depends on mA selected and controls the rate of thermionic emission
why is there a (-) charge behind the focusing cup when the filament infront of it is alrdy (-)
because it will repulse electrons at the filament and make them want to move forward to the anode
where does thermionic emission occur
at the filament
the # of elecs boiled off is determined by….
the mA selected
high mA = more elecs boiled off = more xray photons produced
what is the space charge effect
more likely to happen w high mA,
the thermionic cloud has a neg charge and no more elecs will be boiled off bc the elecs are repulsed by this and do not join the cloud
what is saturation current
filament current has been raised to its max value bc all available elcs have been used
occurs at abt 1000 mA
what is the focusing cup
shallow depression in cathode where filament sits
what is the focuing cup made of
nickel
why does focusing cup have a neg charge
so elecs are repulsed and move to anode, limits thermionic cloud
when us grid controlled or grid biased used
when taking many exposures at once
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M1 L18
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M1 L2 basic elements6
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M1 L334
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cathode36
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anode30
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line focus principle M1L623
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anode heel effect M1L714
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tube preservation21
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M2 L1 scatter19
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M2 L2 collimator31
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M2 L3 intro to grids26
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M2L4 grid formulas14
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M2 L523
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M2 L6 grid errors14
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M3 L1 & 231
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M3 L3 & 416
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M3 L520
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M4 L1 & 230
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M4 L315
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M4L4 & questions from review15
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M5 L1, 2, & 329
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M5 L423
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M5 L5-732
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M6 L1-338
