LECTURE 5: X-RAY PRODUCTION Flashcards Preview

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Flashcards in LECTURE 5: X-RAY PRODUCTION Deck (48):
1

What is kVp?

It is the potential difference between the cathode and the anode

2

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

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

3

Where does the KE of e- come from?

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

4

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

high-voltage generator

5

What is KE of e- called?

Kilo-electron-volts - keV

6

T or F: kVp is proportional to keV

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

7

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

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

8

Formula for KE?

KE = 1/2m v^2 JOULES

9

What is the units for KE?

Joules

10

Do all e- have the same mass?

YES!!! Always

11

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

It will quadruple! x4 because it is ^2
i.e. 5^2 = 25 but 10^2 is 100

12

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

It will double

13

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

Stays the same!

14

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

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

15

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

True - more than half

16

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

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

17

What is coulomb interaction?

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

18

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

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

19

Describe what interaction makes characteristic x-rays

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

20

All atoms have same binding E. T or F?

FALSE - "Characteristic" of each atom - they have diff properties!

21

Why is it called "characteristic" x-rays?

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

22

What does "ISOPROPIC" x-ray production mean?

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

23

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

the proton positive charges

24

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

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

25

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

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

26

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

YES- characteristic x-rays!

27

What is the concept of brems that releases energy?

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

28

What are white radiations?

Brem x-rays

29

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

Large wavelength and low freq

30

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

Energy is in the form of a photon

31

T or F? Coulomb force varies strongly with distance

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

32

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

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

33

Can an e- hit the nucleus?

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

34

Is the brems process poly or monoenergetic?

Poly - there are many diff energies being released

35

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

1. kVp (max energy)
2. Atomic number

think about it - we need the target and we need the energy to hit it

36

How is efficiency measured?

Ratio between the radiative energy loss : collisional energy loss

37

Why are there different energies on the x ray spectrum?

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

38

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

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

39

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

Low energy filtered out by window + surroundings

40

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

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

41

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

TRUE - we only want K shell!

42

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

TRUE

43

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

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

44

Theoretically, how should an x-ray spectrum look?

negative linear graph with characteristic spikes in them

45

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

Radiation vs Collision loss

46

Are collision or radiation loss more common?

Collision - characteristic

47

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

TRUE

48

How to measure efficiency of x-ray production?

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