The XRay Tube

What end of the tube is the cathode?

The negative end

What charge is the focusing cup?

Negative

What is the cathode filament made of?

Mostly tungsten and thorium

What is the average length of the small coil filament?

0.1-0.5mm

What is the average length for the large coil filament?

0.4-1.2mm

What is the maximum mA station for filament currents?

1000-1200

What end is the Anode end?

Positive end

What is the anode target is made of?

Tungsten-rhenium alloy

How fast does the anode rotate?

3400 rpms

What is the atomic number of tungsten?

74

What is the melting point of tungsten?

3410°C

What are the good properties of tungsten?

High atomic number, high melting point, good heat dissipation.

What is insulating oil used for?

To help dissipate heat?

What is the federal regulation for the amount of leakage radiation allowed for an xray tube?

Less then 100mR/hour at 1 meter from the tube.

How are cray emitted from the focal spot?

Isotropically

What is the actual focal spot?

the actual area on the anode which is struck by the electron stream

Why do you want the actual focal spot larger?

To help with heat distribution

Effective focal spot

Is what is projected down from the tube and is always smaller do to beveling the anode, thus improving sharpness of detail.

What is the anode heel affect?

A variation in intensity of the output along the longitudinal tube axis

At what end is the intensity greater?

At the cathode end

What is the cause of the anode heel effect?

Because a large percentage of photons are absorbed by the anode.

What is the variance between the cathode and anode end of the tube?

40%

When is the anode heel effect more pronounced?

Smaller anode angles, shorter SIDs, larger image sizes.

What is the single phase heat unit equation?

mAs•kVp

What is the equation for the three phase heat unit?

mAs•kVp•1.35

What is the high frequency heat unit equation?

mAs•kVp•1.40

What are common tube failures?

Cracking of the anode, pitting or meting of the anode, electrical spark over.

What is the cause of cracking of the anode?

Improper tube warm up, too much heat on a cold anode.

What is the cause of melting of the anode?

When the anode fails to rotate during the exposure. The warped ball bearing fail, usually due to excessive rotoring

What is the cause of electrical spark over?

Due to tungsten atoms “plating” on the inside of the glass window.

What is the most common cause of tube failure?

Filament burn out

What is electromagnetic radiation?

Energy emitted and transferred through matter in the form of a wave. Travels at the speed of light. No mass

What is ionizing radiation?

Capable of removing and orbital electron from an atom when it interacts.

What are the four types of ionizing radiations?

Xray (electromagnetic), gamma ray (electromagnetic), alpha particle (particulate), beta (particulate)

Electron in the k-shell have:

The lowest energy total with the highest binding energy.

With each successive shell:

total electron energies increase and binding energies decrease.

What two interactions produce X-rays:

Bremstahling and characteristic

What is bremstrahling radiation?

When the incident electron is slowed by a positively charged nucleus, lost kinetic energy converted into xray energy.

What kind of spectrum does beams radiation create?

Continuous spectrum

What kind of spectrum does characteristic radiation create?

Discrete emission spectrum

What is characteristic radiation?

When the incident electron ejects and inner shell electron and an outer shell fills a vacancy

How do you calculate the energy of the photon emitted for a characteristic xray photon?

The difference between the two binding energies

What percent of X-rays are produced through brems interactions

85% except in settings below 70kvp

What percent of the time do characteristic interactions make X-rays?

15% of the time

At what technique does characteristic interactions occur?

Only occurs in techniques using 70kvp or higher

What is the effect of mA on emission spectrum?

Changes beam amplitude but average energy stays the same

What is the effect of kV on the emission spectrum?

Changes beam amplitude and average energy.