Week 6- X-Ray Photon Production

Question 1

List components of a diagnostic X-ray

Answer 1

Tube insert
Tube housing (shield)
Light beam diaphragm

Question 2

Describe tube housing

Answer 2

Provides protection from RADIATION and ELECTRICAL HAZARDS resulting from tube insert

Question 3

Describe light beam diagrpham

Answer 3

Provides protection from radiation hazards from tube insert

(Filters - remove lobe energy

Reduces irradiated areas from scattered radiation)

Controls field size of Beam/ reduces area irradiated

Protects body parts not required on radiograph

Question 4

Is anode or cathode positive

Answer 4

ANODE

Question 5

Describe X-ray photon production

Answer 5

X-Ray photons are produced when fast-moving electrons [ accelerated from thecathode ] are suddenly stopped by theimpact with a metal target [ the anode ]

The Kinetic Energy (KE) of the electrons isconverted into X-Ray photons (≈ 1%) andinto heat (≈ 99%

Question 6

Describe thermionic emission

Answer 6

E- emitted from cathode by tHERMONIC EMMISION

Material is heated, KE atoms^, ^ collisions
-outer e- loosely bound
-collisions of atoms near material has sufficient KE to cause some e- to be LIBERATED
-each e- LIBERATED will leave material with a positive charge

Question 7

Describe thermionic emmission- space charge effect

Answer 7

A state of equilibrium is created where:▪ the rate of electrons that are liberated from the material [ W ]EQUALS the rate of electrons that are attracted back into thematerial [ W ]▪

Thus, an electron cloud [ or space charge ] is created

Question 8

In terms of tHERMONIC emissions, the higher the temperature, the…

Answer 8

Greater KE of atoms
More e- liberated

Question 9

Define thermonic work functiom

Answer 9

Min energy needed to liberate an e- from material

The lower the thermionic work function of a material,the less energy is required to liberate the electronsfrom the surface of a material

Question 10

What does scattered radiation do to image quality

Answer 10

Degrade quality of image

Question 11

What else needs to increase in order to increase tube current

Answer 11

Increase number of e- in the charge space BY INCREASING TEMP OF FILAMENT

Question 12

What does increasing temp of filament do to electrons

Answer 12

Increase temp of filament

Question 13

What causes filament to heat

Answer 13

Passage of the current through the filament

E- are liberated by thermionic emmission

Question 14

Describe the process of the tube current/ filament current

Answer 14

The passage of the current through the filament causesthe filament to heat, with the temperature rise causingelectrons to be liberated by thermionic emission▪ The liberated electrons are drawn towards the positiveanode and form the TUBE CURRENT [ mA ]▪ The liberated electrons are then accelerated towards themetal target to create x-ray photons▪ To be able to increase the tube current, it is necessaryto increase the number of electrons in the chargespace by increasing the temperature of the filament,causing more electrons to be liberated▪ Thus, the tube current [ mA ] selection determines thefilament heating current required to produce therequired mA

Question 15

How do we increase tube current

Answer 15

Increase number of e- own charge space by increasing temp of filament so more e- can be liberated

Question 16

What does kV control

Answer 16

peak potential differenceacross the X-Ray tube [TUBE VOLTAGE]

▪ The higher the kV, the greater the peak potentialdifference, and the greater the force of attractionbetween the cathode filament and the anode▪

Thus, the liberated electrons will strike the anode withgreater KE, producing more energetic X-ray photons

▪ The maximum x-ray photon energy is determined by thetube voltage

Question 17

Describe the process occurring within the target

Answer 17

▪ Each liberated electron arrives at the surface of thetarget material with a kinetic energy determined by thetube voltage [ kV ]

▪ The liberated electrons penetrate several millimetres intothe target material and lose their energy by acombination of processes:

▪ [1] As many very small energy losses, by interactionwith the shell electrons of the atoms in the targetmaterial, constituting unwanted heat and causing a risein temperature]

▪ [2] As large-energy losses producing X-Ray photons,caused by the interaction with either the inner shells ofthe atoms in the target material OR [3] the positiveattractive field of the atomic nuclei within the targetmaterial

Question 18

What happens when filament e- interact with shell e-

Answer 18

they are briefly excited (releasing some KE) before returning to their original shape

Energy emitted is infrared- HEAT

99% energy is heat

Question 19

Describe Bremsstrahlung (braking) radiation

Answer 19

Inelastic collisions with atomic nuclei:

▪ filament electrons are suddenly decelerated ordeflected in the vicinity of the positively chargedatomic nuclei

▪ the deceleration causes the filament electronsto lose some KE, which may be converted intoX-ray photons known as Bremsstrahlung (orbraking) radiation▪

the X-ray photons produced have a range ofenergies [ in keV ] lower than maximum kVsetting

Question 20

Describe max photon energy

Answer 20

Inelastic collisions with atomic nuclei:

▪ a filament electron is suddenly halted byimpacting directly with the positively chargednucleus

▪ the sudden halting causes the filamentelectron to lose all of its KE, which is thenconverted into an X-ray photon

▪ the X-ray photon produced has the maximumpossible energy [ in keV ] equal to themaximum kV setting

Question 21

Describe characteristic radiation

Answer 21

Inelastic collisions with inner shells:

▪ filament electrons can liberate shell electronswhen they have sufficient KE to overcome thebinding energies of the shell electrons

▪ the vacancy left by an ejected inner shellelectron leaves the inner shell unstable

▪ the vacancy is immediately filled by anotherelectron dropping down from a higher shell [ anelectron transition ] with the release of electronPE in the form of an X-ray photon

▪ the energy of the X-ray photon is dependent onthe difference between the binding energies ofthe shells involved in the electron transition

Question 22

Define electron transitions

Answer 22

the energy of the X-ray photon is dependent onthe difference between the binding energiesof the shells involved in the electron transitions

Question 23

What do we use to manipulate size, shape, start and end point of X-Ray spectrum

Answer 23

KV (tube voltage)
MA (tube current)
Z (atomic number)
Filtration
Waveform

Question 24

Symbol for tube voltage

Answer 24

KV

Question 25

Symbol for tube current

Answer 25

MA

Question 26

Symbol for atomic number

Answer 26

Z

Question 27

What happens to the x-ray spectrum when tube voltage is increase

Answer 27

Up and right

^ number of X-ray photons

but increase change in AverageE, Effective E, Maximum E, or Minimum E

Question 28

Equation for voltage

Answer 28

V= i x r

Question 29

What occurs when we increase tube current

Answer 29

X-ray spectrum shifts ^

^ in number of X-ray photons

but no change in AverageE, Effective E, Maximum E, or Minimum E

Question 30

What happens to figrak when target material to lower Z

Answer 30

Reducesnumber of x ray photons
And radiation produced

Question 31

Describe inherent filtration

Answer 31

Low e xray photons are filtered by tube snort and cooling oil surround tube insert

Question 32

What does the quality of Bremsstrahlung radiation represent

Answer 32

The penetrating power of X-RAY Beam