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Radiation Sources Flashcards

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1
Q

NCRP 160

What is the breakdown of the average annual HE in mSv?

A

Natural background

  • Radon ⇒ 2.1 mSv
  • Other ⇒ 1.0 mSv

Artificial

  • Medical ⇒ 3.0 mSv
  • Consumer Products ⇒ 0.13 mSv
  • Occupational ⇒ 0.005 mSv
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2
Q

List three natrual environmental “background radiation” sources.

A
  1. Rocks in the crust of the earth
  2. Radionuclides in air, food and water
  3. Cosmic radiation
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3
Q

What radionuclides contribute to external terrestrial radiation (naturally occurring radionuclides in rocks)?

A
  • Ra-226
  • U-238
  • Th-232
  • K-40
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4
Q

Define

Genetically Significant Dose (GSD)

A
  • Includes only the fraction of the radiation which actually deposits energy in the gonads (ovaries or testes) of persons of childbearing age.
  • Useful when discussing background levels in populations.
  • This GSD number is further reduced by a “weighting factor” which is the probabilty of the exposed individual producing more offspring.
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5
Q

Most of the internal terrestrial radiation comes from which radionuclide (and how much)?

A
  • K-40
  • About 80%
  • The U.S. average GSD from all of the internal emitters, estimated in the 1987 report is 36 mrem year-1
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6
Q

Define

TENORM

A
  • Technologically Enhanced Naturally Occurring Radioactive Material.
  • A material which contains radionuclides that are present naturally in rocks, soils, water, and minerals and that have become concetrated and/or exposed to the accessible environment as a result of human activities.
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7
Q

Define

NORM

A
  • Naturally Occurring Radioactive Material
  • Term used to describe materials containing radioactive materials that exist in the natural environment.
  • NORM is widespread. Sands, clays, soils, rocks and many ores and minerals can contain varying amounts of naturally occurring radionuclides.
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8
Q

What are the chief NORM radionuclides of concern?

A
  • Ra-228, Ra-226, and their daughters (Pb-210 in particular)
  • K-40
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9
Q

What is the limit for airport backscatter X-ray scanners?

A
  • 25 micro-rem per screening
  • Recommended by ANSI N43.17-2009
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10
Q

What radioisotopes are commonly used for illumination devices? Which one produces the highest dose and why?

A
  • Ra-226, H-3, and Promethium-147.
  • Ra-226 produces a much higher genetically significant dose rate than the tritium or promethium (both beta emitters) which is why it is shielded by the case of the luminous device.
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11
Q

Smoking 1.5 packs of cigarettes a day delivers what lung dose?

A
  • 160 mSv per year to the lungs.
  • From Pb-210 and Po-210, alpha emitters that are present in cigarette smoke.
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12
Q

What radionuclides are released into the environment from combusion of fuels?

A
  • Coal burned to generate electrical power generates fly ash which carries measurable levels of Ra-226, Th-232, and isotopes of uranium, lead, and polonium.
  • Radiation doses from the average U.S. coal are about 4 mrem/yr (GSD) with dose rates to the bone of 36 mrem/yr for a person living 500 meters downwind from a 1,000 MW plant.
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13
Q

What radionuclide comprises a smoke detector?

A
  • 1 micro-curie of Am-241.
  • Approximately 0.01 mSv/yr was the 1987 NCRP estimate of GSD to the exposed individuals.
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14
Q

What are the basic components of an X-ray tube?

A
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15
Q

Describe

X-ray tube operation

A
  • X-ray tubes consist of a wire filament (cathode) and target (anode).
  • Cathode (tungsten wire) heats up by passing of an electric current, which releases electrons through therminioic emission.
  • An alternating potential is applied.
  • When the target is positive with respect to the cathode, electrons under Coulombic Force would accelerate across the gap and strike the target.
  • This leads to the emission of bremsstrahlung radiation.
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16
Q

Why is tungsten used as the target in X-ray tubes?

A

The amount of bremsstrahlung produced in an absorber is directly proportional to the atomic number (Z) of the absorber.

Therefore high Z metals which have high melting points are the best choice for X-ray tube targets.

Tungsten hss a Z of 74 and a melting point of 3,370 degrees C.

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17
Q

Medical X-ray machines are divided into what two basic groups?

A
  1. Diagnostic
  2. Therapeutic
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18
Q

21 CFR 1020

Radiation output limits for fluoro machines

A
  • 5 R min-1
    (without an automatic exposure rate control)
  • 10 R min-1
    (with an automatic exposure rate control)
  • 20 R min-1
    (machines with an optional high level control)
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19
Q

What are average patient doses for the following CTs?

  1. Head
  2. Chest
  3. Abdoment
  4. Pelvis
A
  1. Head ⇒ 2 mSv
  2. Chest ⇒ 8 mSv
  3. Abdomen ⇒ 10 mSv
  4. Pelvis ⇒ 10 mSv
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20
Q

What are two criteria for a radioisotope used in nuclear medicine?

A
  1. The chosen isotope should decay by emitting photon radiation predominantly. Any particular radiations (alpha or beta) will be locally absorbed in the organ and contribute to patient dose without contributing to the information signal.
  2. The half-life should be short (in hours). Patient dose is directly proportional to the half-life
21
Q

Equation for Mo-99 to make Tc-99m

A

TC-99m

  • Half-life of 6 hours
  • Photon energy of 140 keV
22
Q

What are common use radionuclides in radiation oncology?

A
  • Ra-226
  • Rn-222
  • Cs-137
  • Ir-192
  • I-125
23
Q

What are the common components of nuclear particle accelerator?

A
24
Q

What is the relationship between accelerated particle energy and potential difference?

A
25
Q

Nuclear Particle Accelerators

What is the ion source?

A
  • Device for producing a plasma of free ions.
  • In positive ion accelerators, it often is of the radiofrequency stripping type.
  • A high frequency alternating potential difference causes sufficient forces on the electrons of a neutral gas so that they break their binding forces (are stripped) to produce positive ions.
26
Q

Nuclear Particle Accelerators

What is the high voltage supply?

A

By connecting a high voltage supply in such a way that a potential difference appears between the ion source and the target section, the ions accelerate toward the target under action of the coulomb force.

27
Q

Nuclear Particle Accelerator

What is the beam pipe?

A
  • An evacuated section through which the accelerated ions pass.
  • A vacuum system removes enough of the air molecules to prevent loss of beam ions due to collisions with these extraneous molecules.
28
Q

Nuclear Particle Accelerator

What are magnets used for?

A
  • As a lens to focus the beam into a tight “pencil”.
  • A deflection force to steer the beam along a desired path of beam line.
29
Q

Nuclear Particle Accelerator

What is the target?

A
  • Where the “useful” work is done.
  • In a research application, the effect of the beam on some object is studied at the target.
30
Q

Nuclear Particle Accelerator

What is the beam dump?

A
  • A section at the end of the beam pipe to remove any remaining energy from the beam and to safely dissipate the resulting heat.
  • It often involves some form of water-cooled apparatus.
31
Q

Nuclear Particle Accelerators

What are the two types of accelerator radiation fields of interest?

A
  1. Prompt Fields
  2. Induced Fields
32
Q

Nuclear Particle Accelerator

What is a prompt field?

A
  • Present only when the nuclear accelerator beam is on.
  • In electron machines, the prompt field is dominated by bremsstrahlung photons at all electron energies.
  • In electron machines operating above 10 MeV, there is an additional problem from neutrons produced in photonuclear reactions caused by high energy brmsstrahlung.
33
Q

Nuclear Particle Accelerator

What is an additional concern in high energy accelerators (>1,000 MeV)?

A
  • Muons are an added complication.
  • Muons are produced from the decay of short-lived pi and K mesons which are produced when the high energy ion collides with the target nuclei.
34
Q

Nuclear Particle Acclerator

What is the induced field?

A
  • Consists of the emissions of radioactive nuclei which have been activated by prompt neutrons striking machine components, the surrounding shielding, and the air inside the accelerator vault.
35
Q

Nuclear Particle Accelerator

What is the decay rate of a typical accelerator once the beam is turned off?

A

Often falls by a factor of 2 in 50 hours.

36
Q

Nuclear Particle Accelerator

What are the common activation products from an accelerator?

A
  • Na-24 is the dominant activation product (gamma emitter) in concrete shields.
  • Air activation products include: O-15, N-13, C-11, Ar-41.
37
Q

1 Watt = _____ fissions sec-1

A

1 Watt = 3.3 x 1010 fissions sec-1

38
Q

Nuclear Reactor

What are the common components of a nuclear reactor?

A

Fuel - Source of U-235

Moderator - Slows down fast neutrons

Coolant - Removes the heat of fission

Reflector - Reduces neutron leakage

Control Rods - Adjusts the value of keff

Shield - Protects operating personnel

39
Q

Nuclear Reactor

What are elements with a high neutron capture probability?

A
  • Boron
  • Cadmium
  • Hafnium
  • Indium
  • Silver
40
Q

Nuclear Reactor

What is enriched uranium?

A

The concentration of the U-235 isotope has been artificially increased above the natural abundance level of 0.72%.

41
Q

Nuclear Reactor

What is Highly Enriched Uranium (HEU) of U-235?

A

U-235 is above 20%

42
Q

Nuclear Reactor

What is “Weapons Grade” U-235?

A
  • U-235 is above 93%
43
Q

Occupancy Factor

Administrative offices; laboratories, pharmacies (work areas); adjacent X-ray rooms, film reading areas, nurse’s stations, x-ray control rooms

(NCRP 145/147)

A

1

44
Q

Occupancy Factor

Rooms used for patient examinations and treatments

(NCRP 145/147)

A

1/2

45
Q

Occupancy Factor

Corridors, patient rooms, employee lounges, staff rest rooms

(NCRP 145/147)

A

1/5

46
Q

Occupancy Factor

Corridor doors

(NCRP 145/147)

A

1/8

47
Q

Occupancy Factor

Public toilets, unattended vending areas, storage rooms, outdoor areas with seating, unattended waiting rooms, patient holding areas

(NCRP 145/147)

A

1/20

48
Q

Occupancy Factor

Outdoor areas with only transient pedestrian or vehicular traffic, unattended parking lots, vehicular drop off areas (unattended), attics, stairways, unattended elevators, janitor’s closets

(NCRP 145/147)

A

1/40

49
Q

List

Five machine parameters that affect radiation exposure from CT, X-ray, and fluoroscopy

A
  • Machine voltage (kVp)
  • Machine current (mA)
  • Beam filtration
  • Beam area (collimation)
  • Machine on time (sec)

Health Physics (17 decks)

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