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CEDO > 3: Ionization > Flashcards

3: Ionization Flashcards

1
Q

What is ionization?

A

Creation of ion pairs - transfer of energy from photon or atom (electron that was forced out of atom)

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2
Q

Ionization can be caused when these types of particles interact with the atom.

A

Alpha/Beta, neutrons and free electrons.

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3
Q

HOW does ionization occur when the particles interact with the atom?

A

Energy transferred from moving particles to orbital electron and dislodges it.

energy received depends on mass, charge and speed

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4
Q

What is specific ionization?

A

Number of ion pairs produced per unit length of a particles path.

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5
Q

What is total ionization?

A

Total number of ion pairs produced along path.

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6
Q

Is ionization through electromagnetic radiation a result of direct collision?

A

No because electromagnetic radiation has no mass.

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7
Q

What is ionization through electromagnetic radiation a result of? (3)

A
  1. Photoelectric process
  2. Compton scattering
  3. Pair production
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8
Q

What is the photoelectric effect?

A

Photon (LOW energy) transfers its total energy (complete absorption) to an electron by colliding with it - photon completely absorbed.

*Excess energy transferred to electron in kinetic energy form.

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9
Q

What is Compton scattering?

A

Photon (MED energy) interacts with orbital electron and dislodges it - photon loses energy* (from interaction) but continues to travel in different direction room.

*Greater than energy required to eject.

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10
Q

What is pair production?

A

Interaction with nucleus.

Photon must have min energy (1.022 MeV) comparable to mass energy of 2 resting electrons.

Destroyed photon creates: electron (-1) and positron (+1)

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11
Q

Describe 3 characteristics of a positron:

A
  1. Short lived
  2. Disappears when collided with free electron
  3. Energy used to create 2 photons of 0.511 MeV each
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12
Q

What is the result of an electron and positron that was created through annihilation of a photon?

A

2 lower energy photons

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13
Q

What is radiation intensity directly proportional to?

A

Activity of radionuclide.

More rays = more ionization

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14
Q

Number of rays available is determined by what?

A

Dose rate

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15
Q

What is energy proportional to?

A

Frequency

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16
Q

What is energy inversely proportional to?

A

Wavelength.

17
Q

What would be considered primary radiation?

A

Photons produced in an X-ray or following a disintegration of a radionuclide.

18
Q

When primary radiation strikes an object, what does the gamma radiation and orbital electron produce?

A

A free electron AND a less energetic photon travelling different direction than incident — which is scattered radiation

19
Q

Amount of an absorber depends on what 3 factors?

A
  1. Original energy of radiation
  2. Density/atomic structure of absorber
  3. Thickness of absorber
20
Q

What is the absorbing material expressed in?

A

HVL and TVL

21
Q

What happens to high energy radiation when passing through a gas?

A

Ionization

22
Q

What does a survey meter measure?

A

Ion pairs

23
Q

What is a scintillator?

A

Absorbs ionizing radiation and converts fraction of absorbed energy into visible/UV protons

24
Q

What type of radiograph do you need when generating X-rays using a low kilo voltage?

A

Radiograph with high contrast.

Low radiation is more attenuated

25
Q

X-ray films for general radiography consist of what?

A
  1. An emulsion made of gelatin
  2. Radiation sensitive silver halide crystals
  3. Emulsion costed on both sides of base in layers about 0.0005” thick
26
Q

With exposure above 150 KV, where does the film need to go?

A

Between 2 thin sheets of lead compound in paper backing.

27
Q

What type of screens are essential in basically ALL radiography with gamma rays?

A

Lead foil screens*

28
Q

What are 3 benefits of lead foil screens?

A
  1. Shorter exposure time than without
  2. Absorb large portion of scattered radiation
  3. Intensifies primary radiation
29
Q

When do you use fluorescent screens in NDT?

A

For very thick specimens.

Fluorescent screens = lower definition

30
Q

What events occur during a photoelectric effect?

A

Incident photon with low energy transfers TOTAL energy to electron in a shell by colliding with it - excess energy transferred to electron in kinetic energy form.

31
Q

What events occur in a Compton effect?

A

Med energy incident photon interacts with orbital electron and dislodges it - Compton electron ends up with kinetic energy, photon of less energy than incident travelling in different direction

32
Q

What is radiographic contrast?

A

Degree of density difference between 2 areas on radiograph.

CEDO (9 decks)

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