LECTURE 5: X-RAY PRODUCTION

Question 1

What is kVp?

Answer 1

It is the potential difference between the cathode and the anode

Question 2

Where does the external energy source to accelerate the e- come from?

Answer 2

generator! high-voltage generator supplies the energy to the cathode to fire e- at anode

Question 3

Where does the KE of e- come from?

Answer 3

As the e- are accelerated to the anode, they gain kinetic energy

Question 4

How are e- accelerated to the anode? Where does its energy come from?

Answer 4

high-voltage generator

Question 5

What is KE of e- called?

Answer 5

Kilo-electron-volts - keV

Question 6

T or F: kVp is proportional to keV

Answer 6

TRUE - the kinetic energy of an e- is proportional to kVp (potential difference between cathode and anode)

Question 7

If the atomic number of the target is higher, does this increase or decrease x-ray production?

Answer 7

Increase because more probability of hitting an e- since theres more of them

Question 8

Formula for KE?

Answer 8

KE = 1/2m v^2 JOULES

Question 9

What is the units for KE?

Answer 9

Joules

Question 10

Do all e- have the same mass?

Answer 10

YES!!! Always

Question 11

Kinetic energy: if you double V, what happens to KE?

Answer 11

It will quadruple! x4 because it is ^2

i.e. 5^2 = 25 but 10^2 is 100

Question 12

Kinetic energy: if you double m (mass), what happens to KE?

Answer 12

It will double

Question 13

If you decrease mass by 1/4, but increase speed by double, what happens to KE?

Answer 13

Stays the same!

Question 14

Do all e- have the same energy if you supply a certain kVp?

Answer 14

No - because it depends on a lot of factors like e- e- interaction, space defect…

Question 15

T or F? e- travel at half the speed of light

Answer 15

True - more than half

Question 16

Where does heat come from when e- interact with target?

Answer 16

Collision with atom but KE incident e- is less than BE of orbital e-; only get excitation

Question 17

What is coulomb interaction?

Answer 17

INDIRECT INTERACTION of electrically charged particles - i.e. electrons with nucleus - Bremsstrahlung x-rays

Question 18

What is the main principle of bremsstrahlung x-rays, what about characteristic?

Answer 18

Brem: coulomb interactions
Characteristic: IONISATION - incident e- collision with orbital e-

Question 19

Describe what interaction makes characteristic x-rays

Answer 19

IONISATION incident e- comes and hits orbital e-; with KE larger than BE, it will eject the orbital e- from the atom

Question 20

All atoms have same binding E. T or F?

Answer 20

FALSE - “Characteristic” of each atom - they have diff properties!

Question 21

Why is it called “characteristic” x-rays?

Answer 21

First, we have incident e- ejecting an orbital e-; (produces heat) then, as each e- from outer shells jump down to fill the space, energy is given off in the form of CHARAC X RAYS

Question 22

What does “ISOPROPIC” x-ray production mean?

Answer 22

Means that e- has no set path when it is ejected; goes wherever they want to

Question 23

What makes outer shell e- want to jump closer to the nucleus?

Answer 23

the proton positive charges

Question 24

Can you get more than one characteristicc x ray during just one interaction?

Answer 24

Of course. because all the e- keep jumping down the spaces!

Question 25

As e- transitions to a lower E state, what happens?

Answer 25

The difference in BE of the e- from outer and inner shell is released as characteristic x-ray photons

Question 26

Is BE unique to given elements/atoms? (Z)

Answer 26

YES- characteristic x-rays!

Question 27

What is the concept of brems that releases energy?

Answer 27

High energetic e- misses outer shell e- > goes close to nucleus > attraction to nucleus causes KE to slow down > e- must release some energy > energy in form of brem x-rays > continuous

Question 28

What are white radiations?

Answer 28

Brem x-rays

Question 29

For brems; a small deflection means ____ wavelength and ____ freq?

Answer 29

Large wavelength and low freq

Question 30

Brems: when e- loses KE, where does it go?

Answer 30

Energy is in the form of a photon

Question 31

T or F? Coulomb force varies strongly with distance

Answer 31

VERY TRUE - this is the basis of brems; closer to nucleus, more force

Question 32

Brems: closer e- comes to nucleus, higher energy emitted

Answer 32

True - decrease distance - increase amount of E lost by incident E - increase photon E (conservation law)

Question 33

Can an e- hit the nucleus?

Answer 33

YES - but very rare. in this occasion, the MAX x-ray energy is released (Emax)

Question 34

Is the brems process poly or monoenergetic?

Answer 34

Poly - there are many diff energies being released

Question 35

X-ray production efficiency is influenced by what 2 main factors?

Answer 35

1. kVp (max energy) 2. Atomic number think about it - we need the target and we need the energy to hit it

Question 36

How is efficiency measured?

Answer 36

Ratio between the radiative energy loss : collisional energy loss

Question 37

Why are there different energies on the x ray spectrum?

Answer 37

1. Random events - K shell or L shell- could be from any | 2. Interactions along the way changes KE of each e-

Question 38

If you increase kVp, low energy x-rays will increase. T or F? Explain

Answer 38

True!!! More e- fired, more interaction, but more heat produced; more interaction between e- (?) - space charge?

Question 39

Explain why the x-ray spectrum shows there are small amounts of low energy x-rays

Answer 39

Low energy filtered out by window + surroundings

Question 40

how do you calculate the peak value in an x-ray spectrum

Answer 40

The peak - will be halfway between one third and half of kVp

Question 41

Characteristic x-rays other than those generated through K-shell transitions are not important in diagnostic imaging

Answer 41

TRUE - we only want K shell!

Question 42

As the E of the incident e- increases above the threshold E for characteristic x-ray production, the % of characteristic x-rays ↑

Answer 42

TRUE

Question 43

How is the peak voltage and lowest energy x ray determined? (Brems)

Answer 43

Peak E of x-ray is determined by the kVp - Emax | Lowest E is not easiy determined due to filter and other interactions

Question 44

Theoretically, how should an x-ray spectrum look?

Answer 44

negative linear graph with characteristic spikes in them

Question 45

Brems vs. Charac: what is the "loss" called?

Answer 45

Radiation vs Collision loss

Question 46

Are collision or radiation loss more common?

Answer 46

Collision - characteristic

Question 47

Brems efficiency is much higher at higher kVp than it is at low

Answer 47

TRUE

Question 48

How to measure efficiency of x-ray production?

Answer 48

Amount of energy emerging as x-rays vs the amount we put into the e- to hit the target