production of X rays

Question 1

Control panel:

contains (3)

Answer 1

 Exposure time, kVp and mA selectors
 Exposure button (dead-man type)
 Indicator light and audible signal

Question 2

Tube head: includes (2)

Answer 2

Power supply + x-ray tube

Question 3

Tube head

within (6)

Answer 3

◦Glass envelope
◦Insulating oil
◦Metal housing
◦Tube window
◦Aluminum filters
◦Lead collimator

Question 4

Cathode (-) (2)

Answer 4

◦ Filament

◦ Focusing cup

Question 5

Filament:

3

Answer 5

◦ Made of tungsten
◦ Source of electrons
◦ Is heated with a low voltage
source and emits electrons at a
rate proportional to its
temperature (thermionic emission).

Question 6

Focusing cup

3

Answer 6

◦ Made of Molybdenum
◦ Negatively charged
◦ Focuses the electrons into a
narrow beam directed to the
focal spot (+).

Question 7

Anode (+) (2)

Answer 7

◦ Tungsten target

◦ Copper stem

Question 8

Tungsten target:

2

Answer 8

◦ Transform the kinetic energy of
the colliding electrons into x-ray
photons.
◦ Highly inefficient: produces 99%
heat and 1% x-rays

Question 9

Copper stem:

1

Answer 9

◦ Works as a thermal conductor
to remove the heat from the
tungsten avoiding target
melting.

Question 10

Why is tungsten a good
target material?
(4)

Answer 10

1. High atomic number
2. High melting point
   (3422°C)
3. High thermal conductivity
4. Low vapor pressure

Question 11

1. High atomic number:

Answer 11

efficient production of x-

rays

Question 12

2. High melting point

(3422°C):

Answer 12

to withstand the

heat produced

Question 13

3. High thermal conductivity:

Answer 13

to dissipate the heat
produced away from the
target

Question 14

4. Low vapor pressure:

Answer 14

helps
maintain vacuum in the
tube at high temperatures.

Question 15

Conditions necessary for X-ray
production
(4)

Answer 15

1. Separation of electrons
2. Production of high-speed electrons
3. Concentration of electrons
4. Sudden stoppage of electron steam

Question 16

Low voltage filament current heats the tungsten filament to incandescence with
resultant separation of outer shell electrons from the tungsten atom (“boiling off”). This
separation of electrons is called

Answer 16

thermionic emission

Question 17

High potential difference is produced between the cathode and anode by applying a

Answer 17

high voltage between them.

Question 18

◦ Electrons are accelerated to approx.

Answer 18

0.5 X speed of light

Question 19

Electron beam is focused by the — and directed towards

the —

Answer 19

focusing cup (negative charge) 
focal spot.

Question 20

Upon striking the focal spot in the anode, the electron stream is stopped abruptly, and
kinetic energy of the electron stream undergoes conversion to

Answer 20

greater than 99% heat

and less than 1% x-radiation.

Question 21

— removes the heat from the tungsten

Answer 21

◦ Cooper stem

Question 22

Focal spot

Answer 22

◦ Area on the target to which the focusing cup directs the electrons and from which the
x-rays are produced.

Question 23

◦ Size if the focal spot is important for

Answer 23

image quality (smaller focal spot, higher spatial
resolution)

Question 24

◦ The smaller the focal spot →

Answer 24

more heat accumulates

Question 25

The smaller the focal spot →more heat accumulates. | ◦ 2 ways to overcome this problem:

Answer 25

1. Rotating anodes | 2. Stationary anodes (line- focus principle)

Question 26

Rotating anode | 2

Answer 26

``` • Allows heat at the focal spot to spread out over a large surface (dark band) • Medical devices ```

Question 27

Line-focus principle (stationary anode) (2)

Answer 27

``` • Angling the target to achieve a smaller effective focal spot than the actual focal spot • Results in sharper radiographic image while maintaining the original surface area of the target for heat dissipation ```

Question 28

Actual focal spot:

Answer 28

the projection of the focal spot perpendicular to the target

Question 29

Effective focal spot:

Answer 29

the projection of the focal spot perpendicular to the electron beam

Question 30

Effective focal spot is always --- than the actual focal spot.

Answer 30

smaller

Question 31

Power supply | 2 principal functions:

Answer 31

``` ◦ Provide a low-voltage current to heat the x-ray tube filament (step-down transformer) ◦ Generate a high potential difference to accelerate electrons form the cathode to the focal spot on the anode (step-up transformer) ```

Question 32

Transformer

Answer 32

◦Electromagnetic device that either increases or decreases the voltage in a circuit.

Question 33

3 types of Transformer in the x-ray unit:

Answer 33

◦ Step-down transformer (filament transformer) ◦ Step-up transformer (high voltage) ◦ Autotransformer

Question 34

Step-down transformer | 3

Answer 34

``` ◦ Used to convert 110 or 220 volts to 3-5 volts to heat the filament (low voltage circuit) ◦ Regulated by the mA switch ◦ increasing mA setting will increase the number of electrons emitted ```

Question 35

Step-up transformer | 3

Answer 35

``` ◦ Used to convert 110 or 220 volts to 60,000-100,000 volts to move the electrons across the tube (high voltage circuit) ◦ Regulated by the kV setting ◦ Increasing the kV will increase the energy of the electrons traveling from the cathode to anode ```

Question 36

Exposure timer: | ◦ Determines

Answer 36

amount of time the high voltage circuit is applied across the x- ray tube (amount of time x-rays are produced)

Question 37

Time delay circuit:

Answer 37

delay of ½ second | to heat the filament

Question 38

Timing circuit:

Answer 38

Actual time of exposure

Question 39

kV (kilovoltage):

Answer 39

controls the acceleration of electrons from cathode to anode

Question 40

mA (milliamperage):

Answer 40

controls heating of the | filament

Question 41

Exposure time:

Answer 41

controls the time in which x-rays are produced