Lecture 2 - Radiation Flashcards
Why is the tube head filled with oil?
Heat transfer from the photon
An incident electron directly striking a tungsten nucleus produces what?
Maximum energy Bremsstrahlung radiation
When the incident electron passes near the atom, but doesn’t hit it, what occurs?
Low energy Bremsstrahlung radiation
When an electron passes close to the nucleus and bend around it, when is produced?
Moderate energy Bremsstrahlung radiation (x-ray photon)
*The electron decelerates and bends, when this occurs, energy is given off
What element is the target for electrons?
Tungsten
Bremsstrahlung Radiation:
High energy
Moderate energy
Low energy
High - Some electrons directly collide with the tungsten nucleus - produces a high energy photon equal in energy to the incident electron
Moderate - Electrons pass close to nucleus - Decelerates and bends electron - Moderate energy photon given off
Low - Electrons pass at a distance from nucleus - deflected and slowed - Low energy photon given off
A 70 kVp tube head will produce x-rays with a max energy of how much?
70 keV of energy
What is characteristic radiation?
Incident electron hits another electron, and kicks it out of its orbital. This creates a void in the orbital, and a lot of energy is released in the form of photons
T/F - Characteristic radiation accounts for only a small fraction of x-ray photons generated.
TRUE
The tungsten characteristic X-ray is found at what photon energy?
59 keV
The cathode is __________
The anode is ___________
Negative
Positive
*This is opposite of common sense
What is the cathode made of?
How does it work?
Tungsten filament and molybdenum focusing cup.
Low voltage heats the filament, and this produces a cloud of electrons. The molybdenum cup focuses the electrons into a narrow beam
What is the anode made of?
How does it work?
Tungsten target and copper stem
Electron stream turned into x-rays and heat
Why is the X-ray tube in a vacuum?
It helps prevent burnout of the filament, also no oxidation
What is the element used as the typical target on the anode?
Tungsten
What is the focal spot?
The point on the target where the stream of X-ray photons originate.
What does the low voltage tube current do?
Heats the tube filament - this generates a stream of electrons b/t the cathode and anode
What does the high tube voltage current do?
It accelerates the electron stream from the cathode to the anode to a level that X-rays can be produced (80,000 volts)
What does the step-down filament transformer do?
Reduces incoming voltage (110-120V) to approximately 3-5 volts needed to heat the filament
What does the step-up transformer do?
Provides large electrical force needed to propel electrons from cathode to anode (from 110-120 V to 60,000 to 100,000 V)
What is the auto transformer and what does it do?
It is controlled by the kVP dial on control panel. It varies the voltage to the step-up transformer to achieve the desired kVp to the tube
What is the most frequent source of malfunction in the X-ray tube?
Filament burnout
*Keep the machine on during the day. More strain occurs when it is repeatedly warmed and cooled by being turned on and off repeatedly
How do you increase the energy of the emitted X-ray beam?
Increase power to the high voltage step up transformer. This increases the acceleration of the electrons from cathode to anode, resulting in an energy increase
Doubling the exposure time _________ the exposure.
Doubles
