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Radio 1 > Rad Physics > Flashcards

Rad Physics Flashcards

1
Q

Z-number is?

A

protons

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2
Q

A-number is?

A

mass number

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3
Q

Higher Z# means what for binding energy?

A

higher

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4
Q

Particulate vs Electromagnetic radiation

A

particulate: alpha, beta, cathode
kinetic energy of small mass

electromagnetic: x-rays, gamma rays, light
electric/magnetic fields

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5
Q

X-rays mass? electric charge?

A

no mass, no charge

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6
Q

Wavelength of xrays

A

0.1A to 0.5A

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7
Q

Bremstrahlung is what interaction? How are x-rays created this way?

A

electron to nucleus interaction

x-rays generated when high velocity electrons interact with high atomic # atoms and decelerate suddenly

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8
Q

characteristic radiation is what interaction? How are x-rays created this way?

A

electron to electron interaction

Direct hit knocks electron out of orbit. When a higher-energy electron fills this spot, the movement to a lower level gives off x-ray.

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9
Q

Two named mechanisms for x-ray production?

A

bremsrahlung and characteristic radiation

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10
Q

Which mechanism creates the greatest source of xrays?

A

Bremstrahlung

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11
Q

In the x-ray tube, the tungsten filament is the…

Tungsten target?

A

Filament - cathode

Target - anode

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12
Q

What is the source of electrons?

A

cathode

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13
Q

What concentrates electrons?

A

focusing cup

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14
Q

what accelerates electrons?

A

high voltage

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15
Q

What is the target to stop electrons?

A

anode

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16
Q

How are electrons generated in the cathode?

A

thermionic: current heats cathode to 2200 C which emits an electron cloud

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17
Q

What does the step down transformer do?

A

Steps voltage down so cathode doesnt melt

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18
Q

What does the step up transformer do?

A

increases potential difference between cathode and anode, increasing speed of electrons

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19
Q

effective focus spot is _____ to improve ____?

A

small to improve image sharpness

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20
Q

actual focus spot is _____ to increase _____?

A

large to increase heat dissipation

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21
Q

Factors controlling x-ray beam (5)

A 
Tube voltage (KVp)
Exposure time (S)
tube current (mA)
Filtration
Collimation
22
Q

Tube voltage effect on x-ray beam?

A

shifts curve up and to right - greater # of higher energy photons

23
Q

HVL - characterizes what about an xray beam?

A

penetrating quality and mean energy, found by thickness of an absorber that reduces quantity of photons by half

24
Q

As KVp increases, HVL…?

A

increases

25
Q

Tube current effect on xray beam?

A

Increases # photons

26
Q

Exposure time vs # photons recieved?

A

Double exposure = double photons

27
Q

FIltration filters out what?

A

low energy electrons that don’t contribute to radiograph but do to patient risk

28
Q

What is responsible for inherent filtration in xray tube?

Added filtration in x-ray tube?

A

Inherent - glass/oil

Added - aluminum disk

29
Q

Filtration levels for 50-70 kVp?

70+?

A
  1. 5mm aluminum equivalent

2. 5mm

30
Q

Filtration increases exposure time by what?

Reduces pt dose by?

A

50% more exposure, 80% reduced dose

31
Q

Filtration effect on photon curve?

A

down and peak to right

32
Q

collimator does what?

A

metallic barrier with aperture that

  1. reduces size and modifies shape of beam
  2. reduces volume tissue irradiated
  3. improves image quality
33
Q

Distance versus dose of xray

A

intensity inversely proportional to square of distance

34
Q

Should put x-ray tube how far from pt?

A

as close as possible without touching

35
Q

Types of interaction of xrays with tissue (3)

A

Coherent (7 %)

Photoelectric effect (27%)

Compton (57%)

(other 9% is no interaction)

36
Q

Coherent scattering is what?

A

Incoming low energy electron comes near outer electron, , causes it to vibrate at same frequency and dies. The new electron radiates a new x-ray with same frequency and energy as old xray.

37
Q

Which type of interaction is the primary contributor to image formation?

A

Photoelectric effect

38
Q

How does photoelectric effect work?

A

incoming photon collides with inner shell electron
electron absorbs all photon’s energy and is ejected (ionization)
Higher energy electron fills vacancy, emits characteristic radiation
Recoil electron (photoelectron) also given off, all absorbed.

39
Q

Photoelectric effect depends on what 3 things?

A
  1. wavelength/energy of photon energy/kVp
  2. Atomic # of material
  3. density of material

PE = Z^3/kVp^3

40
Q

Compton scattering works how?

A

Incoming photon interacts with outer shell electron, electron ejected
Incident photon deflected with lower energy
Scattered photons travel in all directions

41
Q

What do the scattered photons from compton scattering contribute to image?

A

no useful information due to altered path; only fogging/darkening

42
Q

Distinguishing radiopaque/radiolucent on film due to?

A

differential absorption

43
Q

Exposure defined as?

A

capacity of x-rays to ionize air - amount of charge per mass of air, coulombs per kg

44
Q

Conventional unit of exposure?

A

Roentgen: 2.58 x 10e-4 C/Kg

45
Q

Absorbed dose defined as

A

amt energy imparted by ionizing radiation to a mass of tissue.

46
Q

Absorbed dose unit?

A

1 Gray (Gy) = 1 joule of energy deposited in 1 kg

1 Gray = 100 Rads

47
Q

Equivalent dose measures? How to calculate?

A

biological effectiveness of different types of radiation

Sum of products of absorbed dose (Gy) and quality factor (QF)

48
Q

Unit of equivalent dose?

A

Rem, 100 Rem = 1 Sv (Sievert)

49
Q

Effective dose measures? How to calculate?

A

compares risk of different types of expsoures

Sum of products of equivalent dose to each organ and tissue weighing factor

50
Q

Effective dose takes into account (3)

A

Volume
Radiosensitivity of tissue irradiated
Biologic effectiveness of radiation

51
Q

For dental x-rays, 1 roentgen = ? rads = ? rems?

A

1 roentgen = 1 rad = 1 rem

52
Q

For dental xrays, 100 rads = ? Gy = ? Sv

A

100 rads = 1 Gy = 1 Sv

Radio 1 (6 decks)

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