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Radiation Protection (Physics) > Lecture 9, 10, 11. Radiation Detectors > Flashcards

Lecture 9, 10, 11. Radiation Detectors Flashcards

1
Q

What are the 2 categories of radiation measuring instruments?

A
  1. Survey Instruments (Measures rate at which radiation events occur)
  2. Dosimeters (Measures cumulative radiation dose)
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2
Q

Diagram of Gas-Filled Detectors

A
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3
Q

How do Gas-Filled Detectors work?

A
  1. A high voltage is placed between anode and cathode
  2. Radiation ionizes gas in the detector
  3. Positive ions are attracted to cathode, free electrons are attracted to anode
  4. Collected charges form a small current
  5. Current is measured and displayed as a signal
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4
Q

T or F. The larger the chamber, the more gas molecules there are for ionization and hence more sensitive

A

True

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5
Q

T or F. A pressurized chamber has more gas molecules, hence more sensitive

A

True

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5
Q

What are the 3 types of Gas-Filled Detectors?

A
  1. Ionization chamber
  2. Proportional counter
  3. Geiger-Muller detector
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6
Q

The Voltage Curve

A
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7
Q

Name 2 examples of ion chamber detector

A
  1. 6cc chamber
  2. 180cc chamber
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8
Q
A
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8
Q

How much voltage is generally applied in the ion chamber region?

A

300 volts

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9
Q

How much voltage is normally applied in the proportional counter region?

A

900 - 1300 volts

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10
Q

In the proportional region, decreasing the gas pressure _________ the multiplication

A

Increases

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11
Q

T or F. The proportional counter is used normally in neutron detectors

A

True

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12
Q

What substance is used to stop the continuous discharge that is present in the Geiger Muller tube

A

Alcohol

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13
Q

Dead time + Recovery time =

A

Resolving time

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14
Q

List 3 advantages of the ion chamber

A
  1. Simple and accurate
  2. No dead time
  3. Can distinguish between alpha and beta pulses
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15
Q

What is the main disadvantage of the ion chamber?

A

Poor sensitivity to low exposure rates

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16
Q

List 2 advantages of the proportional counter

A
  1. Can discriminate between high and low LET photons
  2. Higher sensitivity than ion chamber
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17
Q

List 2 disadvantages of the proportional counter

A
  1. Requires very stable electronics
  2. Expensive and fragile
18
Q

List 3 advantages of the GM tube

A
  1. Inexpensive
  2. Little or no pulse amplification needed
  3. Useful for finding lost sources
19
Q

List 2 disadvantages of GM tube

A
  1. Saturation at high dose rates
  2. Limited life
  3. Dead time
20
Q

What detector is ideal for measuring the AMOUNT of radiation from a source?

A

Ion chamber

21
Q

What detector is ideal for measuring the AMOUNT of radiation and its ENERGY?

A

Proportional counter

22
Q

What detector is ideal to know if there’s radiation in an area and if it is too high

A

Geiger-Muller tube

23
Q

What is scintillation?

A

When a material emits a flash of light immediately in response to the absorption of ionizing radiation

24
Q

Scintillation Detectors

25
Q

List the sequence of events of scintillation

A
  1. Photon enters the crystal and imparts some or all its energy to an atomic electron
  2. Electron dissipates its energy through excitations and other processes
  3. De-excitation occurs emitting light
  4. Light strikes photo-cathode of photomultiplier tube (PMT)
  5. Photo-cathode (compound of Cs, Sb, Bi) emits electrons
  6. Electrons are drawn towards dynodes by a high positive voltage
  7. When electrons strike dynode more electrons are displaced by ‘secondary emission’ and they are attracted to the next dynode, and so on
  8. Anode collects an amplified pulse whose size is proportional to the energy deposited
26
Q

What are the advantages of scintillators?

A
  1. Enhanced sensitivity
  2. Can differentiate between different types of radiation
27
Q

What are the disadvantages of scintillators

A
  1. Relatively expensive
  2. Fragile
  3. Very sensitive to light leaks
28
Q

What is the main advantage of liquid scintillation counters?

A

They have nearly 100% detection efficiency for beta radiation

29
Q

List the process of Liquid Scintillation

A
  1. The radioactive sample is added to the scintillation cocktail
  2. Beta particles are emitted, which cause solvent molecules to become excited
  3. The energy of the solvent molecules is transferred to the fluor molecules, which in turn emit light
  4. The jar is placed inside a scintillation counter, which captures and digitizes the light photons
30
Q

What are the uses of gamma spectroscopy

A
  1. Particle energy and spectrum measurements
  2. Nuclide identification
  3. Activity measurements
  4. Concentration measurements
31
Q

List the Steps in Gamma Spectroscopy Processing Chain

A
  1. Detector
  2. Pre-amplifier
  3. Amplifier
  4. ADC (digitizer)
  5. MCA
  6. Image
32
Q

The Gamma spectrum

33
Q

What is the photopeak?

A

The peak which results from photoelectric interactions

NB: They are used to identify the radionuclides

34
Q

T or F. With photopeak, the energy deposited is practically the same as energy emitted

35
Q

What is the Compton continuum?

A

The portion of the spectrum which is produced by Compton scattering within the detector volume

36
Q

What is the Compton edge?

A

The portion of the spectrum which corresponds to the Compton scattering event within the detector volume

37
Q

What is Backscatter Peak?

A

The portion of the spectrum which corresponds to the Compton scattering event in the materials surrounding the detector with scattering angles greater than about 110-120 degrees

38
Q

At what energy does the backscatter peak occur?

A

180-250 keV

39
Q

What other peaks happen inside the detector volume?

A
  1. Single escape peaks
  2. Double escape peaks
40
Q

What other peaks happen in the material surrounding the detector?

A
  1. Annihilation peaks
  2. X-ray peaks
41
Q

What is the main use of Alpha Detectors?

A

For contamination measurements

42
Q

What is radioactive contamination?

A

Deposition of radioactive material in any place where it is not supposed to be

43
Q

List the types of neutron detectors

A
  1. Proportional counter
  2. Fission counter
  3. Activation foil
  4. Bubble detector
44
Q

What two compounds are normally involved in neutron detectors?

A
  1. Helium-3
  2. Lithium flouride (LiF)
45
Q

Types of radiation and their ideal instruments:

A

Gamma - Gamma spectroscopy
Beta - Liquid scintillator
Alpha - Scintillator
Neutron - Proportional counter
Contamination - Alpha detector

Radiation Protection (Physics) (9 decks)

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