Production of X-Rays Part I

Question 1

what is on the control panel

Answer 1

• exposure time, kVp, and mA selectors
• exposure button
• indicator light and audible signal

Question 2

what makes up the tube head

Answer 2

power supply and x ray tube

Question 3

where is the insulating oil located

Answer 3

outside the X ray tube and transformers

Question 4

what is inside the xray tube

Answer 4

a vacuum

Question 5

what is in the tube head

Answer 5

• glass envelope
• insulating oil
• metal housing
• tube window
• aluminum filters
• lead collimator

Question 6

what does the aluminum filter do

Answer 6

filters X ray and removes low energy X rays from the whole beam, so only those that have sufficient energy can exit the tube head

Question 7

what is the x ray tube made of

Answer 7

glass

Question 8

what is the tube head made of

Answer 8

metal

Question 9

what does the oil do

Answer 9

dissipates the heat generated in the tube head

Question 10

what is in the cathode

Answer 10

filament and focusing cup

Question 11

what is the filament made of

Answer 11

tungsten

Question 12

what is the source of electrons

Answer 12

the filament

Question 13

how are electrons emitted from the cathode

Answer 13

filament is heated with a low voltage source and emits electrons at a rate proportional to its temperature - called thermionic emission

Question 14

what is the focusing cup made of

Answer 14

molybdenum

Question 15

what is the charge of the focusing cup

Answer 15

negative

Question 16

what does the focusing cup do

Answer 16

focuses the electrons into a narrow bean directed to the focal spot

Question 17

what charge is the focal spot

Answer 17

positive

Question 18

what is in the anode

Answer 18

tungsten target and copper stem

Question 19

what does the tungsten target do

Answer 19

• transform the kinetic energy of the colliding electrons into Xray photons

Question 20

how efficient is the tungsten target

Answer 20

very ineffective. produced 99% heat and 1% Xrays

Question 21

what does the copper stem do

Answer 21

works as a thermal conductor to remove the heat from the tungstem avoiding target melting

Question 22

why is tungsten a good target material

Answer 22

• high atomic number: efficient production of X rays
• high melting point - 3422 C- to withstand heat in tube
• high thermal conductivity: to dissipate the heat produced away from the target
• low vapor pressure: helps maintain vacuum in the tube at high temperatures
• cheap

Question 23

what are the conditions necessary for X ray production

Answer 23

• separation of electrons
• production of high speed electrons
• concentration of electrons
• sudden stoppage of electron steam

Question 24

what happens in separation of electrons

Answer 24

• thermionic emission
• step down transformer provides the voltage

Question 25

how much voltage is supplied from the step down transformer

Answer 25

6-12 volts

Question 26

describe the production of high speed electrons

Answer 26

- high potential difference is produced between the cathose and anode by applying a high voltage between them - electrons are accelerated to approximately 1/2 speed of light

Question 27

what does the kVp stand for

Answer 27

difference between the anode and the cathose

Question 28

what is usually the kVp

Answer 28

60-90

Question 29

describe the concentration of electrons

Answer 29

- electron beam is focused by the focusing cup (negative charge) and directed towards the focal spot

Question 30

describe the sudden stoppage of electron steam

Answer 30

- upon striking the focal spot in the anode the electron steam is stopped and kinetic energy of the electron steam undergoes conversion to greater than 99% heat and less than 1% x-radiation

Question 31

what removes the heat from tungsten

Answer 31

copper stem

Question 32

the smaller the focal spot the _____ of the image

Answer 32

higher resolution

Question 33

what is the focal spot

Answer 33

the area of the target to which the focusing cup directs the electrons and from which the xrays are produced

Question 34

the smaller the focal spot the more ___ accumulates

Answer 34

heat

Question 35

what are 2 ways to overcome heat accumulation with a smaller focal spot

Answer 35

- rotating anodes - stationary anodes - line focus principle

Question 36

what does the rotating anode do and where is it found

Answer 36

- allows heat at the focal spot to spread out over a large surface - medical devices

Question 37

what is the line focus principle (stationary anode)

Answer 37

- angling the target to achieve a smaller effective focal spot than the actual focal spot

Question 38

what does a stationary anode result in

Answer 38

sharper radiographic image while maintaining the original surface area of the target for heat dissipation

Question 39

what is the actual focal spot

Answer 39

the projection of the focal spot perpendicular to the target

Question 40

what is the effective focal spot

Answer 40

the projection of the focal spot perpendicular to the electron beam

Question 41

how does the effective focal spot compare to the actual focal spot in size

Answer 41

the effective is always smaller

Question 42

what are the 2 functions of the power supply

Answer 42

- provide a low voltage current to heat the x ray tube filament - step down transfomer - generate a high potential difference to accelerate electrons from the cathose to the focal spot of the anode- step up transformer

Question 43

what is the transformer

Answer 43

electromagnetic device that either increases or decreases the voltage in a circuit

Question 44

what are the 3 types of transformers in the xray unit

Answer 44

- step down transformer - filament transformer - step up transformer - high voltage - autotransformer

Question 45

what does the mA control

Answer 45

the amount of energy in the step down transformer

Question 46

what happens if you increase the mA

Answer 46

more energy through the transformer the higher voltage through the filament and the higher number of electrons -> modifies the AMOUNT of X rays produced

Question 47

what does the kVp modify

Answer 47

step up transformer and ENERGY of the X ray

Question 48

what happens if you increase kVp

Answer 48

greater difference between anode and cathose -> electron will be more attracted to the anode -> electron has more energy -> Xray will be more energetic -> modified ENERGY of X ray

Question 49

what does the step down transformer do

Answer 49

used to convert 110 volts to 3-5 volts to heat the filament

Question 50

what does the step up transformer do

Answer 50

used to convert 110 volts to 60,000-100,000 volts to move the electrons across the tube

Question 51

what does the exposure timer determine

Answer 51

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

Question 52

what is the time delay circuit

Answer 52

delay of 1/2 second to heat the filament

Question 53

what is the timing circuit

Answer 53

actual time of exposure

Question 54

what affects number of X rays

Answer 54

time and mA

Question 55

what affects energy of x rays

Answer 55

kVp

Question 56

what does kV control

Answer 56

the acceleration of electrons from cathode to anode

Question 57

what does mA control

Answer 57

the heating of the filament

Question 58

what does exposure time control

Answer 58

the time in which xrays are produced