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17 Cards in this Set
- Front
- Back
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What are the 3 basic tenets of radiation safety?
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1. Decrease time spent near a source
2. Increase distance from a source 3. Use shielding |
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What does ALARA stand for?
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As Low As Reasonably Achievable
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Exposure has a _____ relation to length of time.
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Linear relation
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The intensity of radiation is inversely proportional to the distance from a point source.
If distance is doubled, the intensity is quartered |
Inverse Square Law |
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The exposure rate at a standard distance from a unit of radioactivity of a specific radionuclide
Units are in R⋅cm^2 / mCi⋅hr |
Specific exposure rate constant or gamma constant
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What is the dose rate (DR) formula?
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Gamma constant (R⋅cm^2 / mCi⋅hr)
Activity (mCi) Distance (cm) |
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A specific exposure rate constant that neglects the contribution from low energy photons is indicated by a subscript for the energy cutoff in keV. How would you interpret this?
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Any photons with energies below 20 keV we are ignored
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What are the 3 ways that energy is lost?
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1. Photo electric - photons hit something hard
2. Compton - Low energy protons hit outer orbital electrons and scatter 3. Pair production |
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Density
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ρ = gram/cm^3
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Density thickness
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ρ thickness = gram/cm^2
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The fraction of the number of photons removed from the radiation field per cm of absorber.
It is specific for the energy of photon and the type of absorber |
The linear attenuation coefficient (μ)
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What are the units for linear attenuation coefficient?
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1/cm (thickness of shield is put in denominator)
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The fraction of the number of photons removed from a radiation field per unit of mass of absorber
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Mass attenuation coefficient
μ / ρ = cm^2/gram |
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I = intensity after shielding
Io = initial intensity e = 2.718 μ = linear attenuation coefficient in cm^-1 x = thickness of shield in cm |
Shielding formula |
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The thickness of a shielding material necessary to reduce the incident radiation intensity by 1/2.
It is specific to energy and absorber |
Half value layer (HVL)
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How is the half value layer related to the linear attenuation coefficient?
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HVL = 0.693 / μ
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Thickness required to reduce exposure to 1/10th its original value
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Tenth Value Layer
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