Production of X-rays

Question 1

What is the atomic number?

Answer 1

number of protons
what determines identity of atom

Question 2

What is the atomic mass?

Answer 2

protons + neutrons

Question 3

What is the binding energy?

Answer 3

minimal amount of energy required to remove an electron from its shell

Question 4

Which shell is the most tightly bound?

Answer 4

K

Question 5

How much energy does it take to remove a K shell electron in Tungsten?

Answer 5

70,000 eV // 70 keV

Question 6

How is electron binding energy related to atomic number?

Answer 6

proportionally: higher atomic number = more protons –> higher atomic binding energy

Question 7

What describes creating a positive & negative ion by removal of an electron from a neutral atom?

Answer 7

ionization

Question 8

What is the transmission of energy through space in a vacuum & matter?

Answer 8

radiation

Question 9

What are the two forms of radiation?

Answer 9

wave & quantum

Question 10

Describe properties of the wave theory.

Answer 10

explains propagation of radiation
radiation in form of waves
no mass
speed of light

Question 11

Describe properties of quantum theory.

Answer 11

explains the interaction of radiation with matter
considers radiation small bundles of energy called photons: mass & travel in straight/diverging lines at speed of light

Question 12

What is high energy radiation?

Answer 12

high frequency & short wavelength

Question 13

What is low energy radiation?

Answer 13

low frequency & long wavelength

Question 14

How are frequency & wavelength related in wave theory?

Answer 14

inversely proportional

Question 15

Where does the electromagnetic spectrum become ionizing?

Answer 15

blue light (ultraviolet spectrum)

Question 16

List the electromagnetic spectrum from lowest energy to highest.

Answer 16

radio, micro, infrared, visible, ultraviolet, x-ray, gamma

Question 17

In the quantum theory of radiation are the particles charged?

Answer 17

they can be, but neutrons & x-rays are not

Question 18

What is the heaviest & most charged particle of radiation?

Answer 18

alpha

Question 19

What is the linear energy transfer (LET)?

Answer 19

ionizing rate: low LET for x-rays allows particles to move through tissue easily to reach receptor

Question 20

How is contrast created when considering the particle theory?

Answer 20

some energy/x-rays remain in tissue…cannot penetrate & remain trapped

Question 21

What particle has the highest LET and why?

Answer 21

alpha: electrical charge & weight

Question 22

What are the factors that lead to higher LET?

Answer 22

low velocity, higher charge, bigger size –> less penetration because lose energy over short distances

Question 23

US law states that x-ray machines must have what features?

Answer 23

dead-man type exposure button
indicator light
audible sound

Question 24

What is located inside the tube head?

Answer 24

power supply & x-ray tube

Question 25

Where is the step up transformer?

Answer 25

anode end

Question 26

Where is the step down transformer?

Answer 26

cathode end

Question 27

What charge are the cathode & anodes?

Answer 27

cathode = negative anode = positive

Question 28

Where are the electrons produced?

Answer 28

cathode

Question 29

What is the purpose of the aluminum filter?

Answer 29

filters non-useful x-rays so only the ones that will create an image exit the tube head

Question 30

What is in the cathode?

Answer 30

focusing cup (Mb) negatively charged filament (tungsten)

Question 31

Where is the source of electrons?

Answer 31

filament

Question 32

How are electrons produced?

Answer 32

thermionic emission

Question 33

How do we make the filament hotter to create more electrons?

Answer 33

increase the voltage/energy

Question 34

Which transformer heats up the filament?

Answer 34

low energy / step-down

Question 35

What is at the anode end?

Answer 35

tungsten target & copper stem

Question 36

How efficient is the tungsten target at transferring kinetic energy of the e- into x-rays?

Answer 36

highly inefficient: only 1% become x-rays

Question 37

What is the purpose of the copper stem?

Answer 37

works as a thermal conductor to remove heat & prevent target from melting

Question 38

Where is the source of x-rays?

Answer 38

focal spot

Question 39

What happens if the target melts?

Answer 39

vapors/materials enter the x-ray tube & it is no longer a vacuum

Question 40

Why is a vacuum needed?

Answer 40

we do not want x-rays to interact with anything & want the full energy of them to create our radiographs

Question 41

Why is tungsten a good target material?

Answer 41

high atomic number high melting point high thermal conductivity low vapor pressure

Question 42

The low voltage current heats up the _____ resulting in ______.

Answer 42

tungsten filament separation of outer shell e- from atom

Question 43

How many volts does the low-voltage/step-down transformer produce?

Answer 43

6-12 volts

Question 44

How many volts are required to remove a k shell electron of tungsten?

Answer 44

70kp

Question 45

How is the focal spot related to spatial resolution?

Answer 45

smaller focal spot = higher resolution

Question 46

How do we avoid heat accumulation on the focal spot?

Answer 46

line-focus principle

Question 47

How does the line-principle work?

Answer 47

angling of target creates smaller effective focal spot compared to actual focal spot...results in sharper resolution, while maintaining original surface area of target for heat dissipation

Question 48

The step down transformer is regulated by what switch?

Answer 48

mA

Question 49

Increasing mA setting will increase what?

Answer 49

number of electrons emitted

Question 50

The step UP transformer is regulated by what switch?

Answer 50

kV setting

Question 51

Increasing kV will increase the ?

Answer 51

energy of the electrons traveling from the cathode to the anode

Question 52

If you increase the exposure time, how does that effect the amount of xrays produced?

Answer 52

increases...proportional

Question 53

What term means flow of electrons through an electrical conductor?

Answer 53

electricity

Question 54

What term means the amount of electrons flowing through a conductor per second?

Answer 54

current

Question 55

what is current measured in?

Answer 55

mA

Question 56

What is the path of electrical current?

Answer 56

circuit

Question 57

What is the difference in electrical potential energy between 2 points in an electrical circuit?

Answer 57

voltage (potential difference)

Question 58

What is voltage measured in?

Answer 58

kVp

Question 59

In the USA how many cycles per second?

Answer 59

60

Question 60

T/F During each cycle there is a phase where the anode is positive & attracts e- and a phase where the anode is negative & repels e-?

Answer 60

true

Question 61

T/F the current is constant?

Answer 61

false

Question 62

During what part of the cycle are x-rays produced?

Answer 62

when the anode is positive & attracts e-

Question 63

Why does the current have to be alternating?

Answer 63

because direct current cannot pass through the transformer

Question 64

Why do we need direct current?

Answer 64

once we pass through the transformer we want direct current to ensure that the flow of e- is in one direction towards the anode

Question 65

What device converts the current from alternating to direct?

Answer 65

rectifier

Question 66

How do we create a nearly constant potential?

Answer 66

give multiple pulses after rectification so that the amount of energy/volts stays nearly constant between cathode & anode

Question 67

Why do we want the higher voltage to be constant?

Answer 67

more efficient at producing x-rays & the x-rays will have higher energy

Question 68

Constant potential & direct current means that we can have...?

Answer 68

- shorter exposure times - more consistent beam of intensity - higher mean energy of beam - decreased radiation dose

Question 69

How are x-rays actually produced ?

Answer 69

when the high-speed e- suddenly stop/decelerate close to the nuclei of a high Z # absorbing material (tungsten)

Question 70

What are the 2 mechanisms for x-ray formation?

Answer 70

- Bremsstrahlung - Characteristic

Question 71

Which mechanism describes an e- to nucleus interaction?

Answer 71

Bremsstrahlung

Question 72

Which mechanism describes an e- to e- interaction?

Answer 72

characteristic

Question 73

Describe the spectrum of x-ray energy for Bremsstrahlung radiation?

Answer 73

all the way to max if head on collision occurs (wide distribution/heterogenous)

Question 74

Describe the type of energy emitted by an e- in characteristic radiation?

Answer 74

energy is equivalent to the difference in binding energies of the 2 shells/orbitals

Question 75

Majority of x-ray beams are produced in which way?

Answer 75

Bremsstrahlung radiation