Exam 3 Xray Physics

When x-rays are produced, they are emitted:

 

in all directions

The x-rays emitted through the window are called the ______

useful beam

X-rays that escape through the protective housing are called ______ radiation

leakage

The cathode is the _________ side of the x-ray tube.

negative

The filament is embedded in a metal shroud called the:

focusing cup

What is a space charge?

a cloud of electrons

Which area of the anode is struck by electrons?

target

off-focus radiation

x-rays produced outside the focal spot

most common cause of tube failure:

 

Tungsten vaporization

What could cause rotational friction and an imbalance of the rotor anode assembly?

 

Excessive heating of the bearings

X-rays are produced:

 

isotropically

Considering the line focus principle, which focal spot do you want to be smaller?

 

Effective focal spot size

would it be safe or unsafe to use 80 kVp, 70 mA, and 1 second?

safe

Is X-ray production is an efficient process?

no

What produces a negative space cloud?

heated filament

What selects the filament size on the control panel?

 

Focal spot size

would it be safe or unsafe to use 120 kVp, 200 mA, and 0.2 sec?

unsafe

How long would it take the anode to cool from 65,000 HU to 15,000 HU?

4 minutes

A ______ effective focal spot size will increase image detail.

smaller

purpose of the tube housing

 

reduce leakage radiation and heat to the tube, protect from electrical shock

Explain how the anode rotates

Electromagnets are energized in sequence which turns the rotor in attempt to align with the energized electromagnet.

What is the type of motor used with x-ray tubes?

Induction motor

Electric current is supplied directly to the ____

stator

What is the most common type of anode material?

Tungsten

Why is Tungsten the most commonly used anode material?

high melting point, high heat capacity to withstand heat during production, and high atomic number to increase x-ray production (more interactions)

What is the melting point of the anode material in Celsius?

3400 degrees Celsius

What is the melting point of the anode material in Fahrenheit?

6700 degrees Fahrenheit

What is the anode rotation speed in a general x-ray tube?

 

3400 rpm

1

protective housing

2

leakage radiation

3

high-voltage receptacles

4

tube enclosure/ envelope

5

primary beam

What material is the protective housing made out of?

lead

What material is the anode target made out of?

Tungsten

What material is the cathode filament made out of?

Tungsten

What material is the tube enclosure/envelope made out of?

glass or metal

What are the 3 purposes of the tube protective housing?

1. Electrical insulation

2. Heat protection

3. Reduction of leakage radiation

During x-ray production, what percentage of the interaction is heat and what percentage is photons?

99% Heat

1% X-ray Photons

What are 2 ways the tube housing assists in dissipating heat in the tube?

1. Oil bath

2. Cooling fans

1

Rotor

2

stator

4

cathode

5

anode target/ disc

6

Tube Enclosure/ envelope

7

filament wire

8

Port Window

What is special about the port or window?

It is thinner than the rest of the x-ray tube/enclosure and the useful beam of X-rays is emitted through it

anode charge

positive

cathode charge

negative

focusing cup

negative

1

anode target/ disc

2

electron beam

3

focusing cup

4

filament wire

5

primary beam

What is it called when an x-ray tube has 2 filament wires?  

dual-focus

What part of the x-ray circuit protects the filament wire(s) from breakage/damage?

 

Step-down Transformer

What principle causes the anode to rotate?

 

Mutual Induction

A

Anode angle

B

Anode target/disc

1

electron beam

2

actual focal spot

3

effective focal spot

What principle is this diagram showing?

line-focus

Electric current is supplied directly to the ______

stator

Most of the kinetic energy of electrons is converted into ____.

heat

Only approximately _____ % of electron kinetic energy is used for the production of x-radiation.

1

__________ x-rays are emitted when an outershell electron fills an inner shell void.

Characteristic