Term
| What is the shielding design goal for a controlled area? |
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Definition
P = 0.1 mGy/wk
(based on 5 mGy/yr - designed for a pregnant worker) |
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Term
| What is the shielding design goal for a uncontrolled area? |
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Definition
P = 0.02 mGy/wk (Air Kerma)
Based on public dose limit of 100 mrem/year.
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Term
| What is the maximum limit for leakage radiation? |
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Definition
| 100 mR/h or 0.877 mGy/h at 1 meter from the source. |
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Term
| What distance is used beyond a shielded wall for determining air kerma? |
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Definition
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Term
| What is a primary barrier? |
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Definition
| A barrier that intercepts the primary beam. |
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Term
| What is a secondary barrier? |
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Definition
| A barrier that intercepts secondary radiation (scatter and leakage radiation). |
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Term
| Name 4 factors that affect radiation exposure. |
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Definition
| 1) strength of the source, 2) distance from the source, 3) time - combination of beam on time and the time a person is in the radiation field, and 4) shielding |
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Term
| Recommended size and location of a viewing window. |
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Definition
| 45 x 45 cm2, centered 1.5 m above the floor. |
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Term
| Fluoro shielding only needs to consider _________ radiation. |
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Definition
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Term
| CT shielding only needs to consider _________ radiation. |
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Definition
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Term
| Walls are typically shielded to what height? |
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Definition
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Term
| What distances are used for the nearest person in rooms above, below, and adjacent? |
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Definition
0.5 m above the floor in rooms above the source
1.7 m above the floor in rooms below the source
0.3 m beyond the walls |
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Term
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Definition
| T - the fraction of the time the single most exposed person spends in the occupied area during a 40 hour week. |
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Term
| The occupancy factor allows the design air kerma to be ________ by a factor of ______? |
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Definition
| increased by a factor of 1/T |
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Term
| Occupancy factor for offices, reception areas, control rooms, reading rooms, etc. |
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Definition
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Term
| What has an occupancy factor of 1/2. |
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Definition
| patient exam rooms and treatment rooms |
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Term
| Occupancy factor for corridors, patient rooms, employee lounges, and staff rest rooms. |
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Definition
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Term
| What is the occupancy factor for corridor doors? |
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Definition
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Term
| What is the occcupancy factor for public restrooms, vending areas, storage rooms, unattended waiting rooms, and patient holding areas? |
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Definition
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Term
| Occupancy factor for outdoors, unattended parking lots, attics, stairways, elevators, and janitor closets. |
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Definition
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Term
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Definition
| Time integrated tube current (mA•min) per patient. |
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Term
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Definition
| N - number of patients per 40 hour week. |
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Term
| What is the formula for the weekly workload? |
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Definition
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Term
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Definition
| U - fraction of a primary beam workload that is directed toward a given primary barrier. |
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Term
| What is the Use Factor for mammo and for fluoroscopy? |
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Definition
| U = 0 for both. They both have primary beam stops so there are no primary barriers for these two modalities. |
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Term
| Unshielded primary air Kerma is given as: |
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Definition
Kp(0) = Kp' • U • N / dp2
Kp' is the kerma per patient at 1 meter |
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Term
| Unshielded secondary Air Kerma is given as: |
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Definition
Ksec(0) = Ksec' • N / dsec2
Ksec' is the kerma per patient at 1 meter
Note: no U for secondary radiation |
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Term
| The x-ray beam transmission is given by: |
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Definition
B(x) = K(x) / K(0)
B(x) - transmission through a barrier of thickness x |
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Term
| The formula for calculating the required transmission is given by: |
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Definition
B(x) = K(x) / K(0) = P/T / K(0) = P•d2/ (N•T•U•K')
K(x) - Kerma through barrier of thickness x.
K(0) - Kerma without a barrier
K' - Kerma per patient at 1 m, given in a table. |
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