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Physics Ch 6
Chapter 6 Test #4
23
Physics
Undergraduate 2
10/27/2015

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Term
Heat Units
Definition
kVp x mA x time x rectification constant
Term
Space-charge effect
Definition
As more and more electrons build up in the area of the filament, their negative charges begin to oppose the emission of additional electrons
Term
Anode heel effect
Definition
Where the intensity of radiation is greater on the cathode side
Term
Thermionic emission
Definition
The ejection of electrons from the surface of the wire due to increased heat, causing an electron cloud (also called space charge cloud)
Term
Describe what it means when the x-ray tube is gassy.
Definition
A small percentage of electrons are permanently vaporized from the filament and they contribute to reducing the vacuum, thus making the tube gassy.
Term
What is responsible for the noise during rotor acceleration?
Definition
Long use at high temperatures causes the ball bearing to become imperfectly round.
Term
Describe the focusing cup and what it does.
Definition
A shallow depression in the cathode assembly designed to house the filament.
Term
What is the primary purpose of the focusing cup?
Definition
To narrow the thermionic cloud as it is driven towards the anode.
Term
Atomic number of tungsten?
Definition
74
Term
What part of the anode assembly is located outside the glass housing?
Definition
Stator
Term
What is the maximum allowable radiation leakage from the tube, according to the NCRP?
Definition
100 mR/hr at 1 meter
Term
What is the primary purpose of the tube glass housing?
Definition
Maintain the vacuum between the cathode and the anode.
Term
What material is used for the anode target area?
Definition
Tunsten
Term
Why is it used?
Definition
1. High atomic #
2. High melting point
3. Heat conducting ability
Term
What material commonly makes up the target for mammographic units?
Definition
Beryllium, to avoid attenuating the lower-energy photons.
Term
Where do you measure the "source" when measuring for SID?
Definition
The exact point at which photons are created. The target is considered to be a source point.
Term
What happens if the stator or rotor malfunction?
Definition
Electron stream overheats the target area of the anode focal track. Melting might occur, tube will be destroyed. The end of civilization as we know it!
Term
Describe the filament.
Definition
A small coil of thin thoriated tungsten wire.
Term
What are some desirable characteristics of the material used for filament?
Definition
High melting point and difficult to vaporize.
Term
Cathode end of the tube is what charge?
Definition
Negative
Term
What type of charge does anode have?
Definition
Positive
Term
Why is a rotating anode desirable over a a stationary anode?
Definition
More heat dissipation.
Term
What is a spinning top test used for?
Definition
1. timer accuracy
2. rectifier failure
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