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ONPS YEAR 2 SEM 1 > LECTURE 5: X-RAY PRODUCTION > Flashcards

LECTURE 5: X-RAY PRODUCTION Flashcards

1
Q

What is kVp?

A

It is the potential difference between the cathode and the anode

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2
Q

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

A

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

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3
Q

Where does the KE of e- come from?

A

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

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4
Q

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

A

high-voltage generator

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5
Q

What is KE of e- called?

A

Kilo-electron-volts - keV

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6
Q

T or F: kVp is proportional to keV

A

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

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7
Q

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

A

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

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8
Q

Formula for KE?

A

KE = 1/2m v^2 JOULES

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9
Q

What is the units for KE?

A

Joules

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10
Q

Do all e- have the same mass?

A

YES!!! Always

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11
Q

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

A

It will quadruple! x4 because it is ^2

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

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12
Q

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

A

It will double

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13
Q

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

A

Stays the same!

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14
Q

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

A

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

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15
Q

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

A

True - more than half

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16
Q

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

A

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

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17
Q

What is coulomb interaction?

A

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

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18
Q

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

A

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

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19
Q

Describe what interaction makes characteristic x-rays

A

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

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20
Q

All atoms have same binding E. T or F?

A

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

21
Q

Why is it called “characteristic” x-rays?

A

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
Q

What does “ISOPROPIC” x-ray production mean?

A

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

23
Q

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

A

the proton positive charges

24
Q

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

A

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

25
Q

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

A

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

26
Q

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

A

YES- characteristic x-rays!

27
Q

What is the concept of brems that releases energy?

A

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
Q

What are white radiations?

A

Brem x-rays

29
Q

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

A

Large wavelength and low freq

30
Q

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

A

Energy is in the form of a photon

31
Q

T or F? Coulomb force varies strongly with distance

A

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

32
Q

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

A

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

33
Q

Can an e- hit the nucleus?

A

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

34
Q

Is the brems process poly or monoenergetic?

A

Poly - there are many diff energies being released

35
Q

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

A
  1. kVp (max energy)
  2. Atomic number

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

36
Q

How is efficiency measured?

A

Ratio between the radiative energy loss : collisional energy loss

37
Q

Why are there different energies on the x ray spectrum?

A
  1. Random events - K shell or L shell- could be from any

2. Interactions along the way changes KE of each e-

38
Q

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

A

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

39
Q

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

A

Low energy filtered out by window + surroundings

40
Q

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

A

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

41
Q

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

A

TRUE - we only want K shell!

42
Q

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

A

TRUE

43
Q

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

A

Peak E of x-ray is determined by the kVp - Emax

Lowest E is not easiy determined due to filter and other interactions

44
Q

Theoretically, how should an x-ray spectrum look?

A

negative linear graph with characteristic spikes in them

45
Q

Brems vs. Charac: what is the “loss” called?

A

Radiation vs Collision loss

46
Q

Are collision or radiation loss more common?

A

Collision - characteristic

47
Q

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

A

TRUE

48
Q

How to measure efficiency of x-ray production?

A

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

ONPS YEAR 2 SEM 1 (5 decks)

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