Physics - Chapter 7 Flashcards
What are the essential components or the xray tube?
Support system
Protective housing
Glass or metal enclosure
Protects patient and MRTs from unnecessary radiation exposure and protects from electric shock
Protective housing
T/F
Leakage radiation is less than 1 mGya/s at 1 meter
True
What is the window called where X-rays are emitted?
Useful beam
What are X-rays called that escape through the protective housing?
Leakage radiation
What is the xray tube contained in?
A vacuum
What is the purpose of the xray vacuum?
-Efficient xray production
-Extends tube life
-Less heat produced
What is the length and diameter of an xray vacuum?
Length = 30-50cm
Diameter = 20cm
Negative side of the xray tube
Cathode
What are the 2 primary components of the cathode?
-filament
-focusing cup
What is the size of the filament?
Length = 1-2cm
Diameter = 2mm
Emits electrons when heated
Filament
Outer shell electrons are boiled off the filament and and ejected
Thermionic emission
What are filaments usually made from?
Thoriated tungsten
T/F
The boiling point of tungsten is 3410 degrees Celsius and it does not vaporize easily
True
What charge does the focusing cup have?
Negative
What is it called when an xray tube has two focusing cups side by side?
Small and large focal spot
What is the purpose of the focusing cup?
Negatively charged cup confines electrons to a small area of the anode
Electron cloud formed around the filament
Space charge
What defines the focal spot size?
The size of the filament
What is the size of a small filament?
0.1-1cm
What is the size of a large filament?
0.3-2cm
Positive side of the xray tube
Anode
What are the two types of anodes?
Stationary and rotating
What are the functions of the anode?
Conducts electricity
Radiates heat and X-rays from the target
How much of the kinetic energy is transferred to thermal energy when the electrons strike the target
99%
What are the most common anode materials?
Copper, molybdenum, graphite
Area of the anode struck by the electrons
Target
What is the target made of?
Tungsten
What is the atomic number of tungsten?
74
Thin shaft between the anode and rotor, usually made of molybdenum
Anode stem
What is used to turn the anode?
Induction motor
The part outside the glass or metal enclosure, consists of a series of electromagnets equally spaced around the neck of the tube
Stator
Inside the glass or metal enclosure, a shaft made of bars of copper and soft iron fabricated into one mass
Rotor
Spot of interaction between electrons and anode to produce xray photons
Focal spot
When the target angle is smaller, the effective focal spot is…
Smaller
What is the angle of the target in diagnostic xray tubes?
5-20 degrees
T/F
Effective focal spot increases with with increasing angle
True
The xray beam has a higher intensity on the cathode side than the anode side, what is this called?
Anode heel effect
What can the intensity vary up to with the anode heel effect?
45%
