TM 5-805-12
e. Structural details. Structural details and detailed drawings must show construction of sheet-lead barriers. The
joining of lead materials must be designed to avoid radiation leakage and scattering. All drawings will conform to NCRP
Reports 35 and 49 and will become part of the design drawings. Specific drawings and specifications should be prepared
to:
(1) Indicate the penetration in barriers, such as pipes, ducts, conduits, and louvers, that should be provided with
baffles.
(2) Show where and how lead is to be placed at doors, door openings, door sills, observation windows, corners,
floors and ceilings, and other breaks in the lead barrier.
(3) Specify what should not be pierced by nails, screws, rivets, and bolts, without adequate provisions for
equivalent cover protection.
6. Assumptions.
The following assumptions should be made in determining the shielding requirements for x-ray and gammaray medical
and dental facilities referenced in TB MED 521:
a. X-ray technicians or radiologists will spend their entire work period in the controlled area.
b. Areas adjacent to the radiological rooms are to be occupied by persons nonoccupationally exposed to ionizing
radiation.
c. The x-ray system is operated at its maximum rated peak tube potential (kilovolt peak) and tube current
(milliamperes).
d. The minimum source-to-occupied-area distance is 5 feet.
e. The minimum distance from an unshielded outside wall of a radiographic room to an occupied area is at least 50
feet.
f.
The required thickness of the shielding depends on the quality of radiation, quantity being produced in some
chosen period of time, distance from the tube, degree and nature of occupancy, type of area, and material of which the
barrier is to be constructed.
7. Shielding criteria.
Minimum shielding thicknesses will conform to the following criteria. In all other areas, shielding will be designed for the
specific environment. See tables 1, 2, 3, and 4 for general shielding information.
a. Dental rooms. Guidelines for the thicknesses of barriers (walls, ceiling, and floor) will be determined from NCRP
Report 35 and TB MED 521.
(1) Shielding will cover walls and doors up to 7 feet above the floor.
(2) Ceilings will be covered with lead if space above can be occupied and calculations indicate a need for
increased shielding.
(3) Floors will be covered with lead if space below can be occupied and calculations indicate a need for
increased shielding.
(4) Control booth or protective barrier, including observation window, will have the same rating as specified
shielding. Control booth will be arranged so that radiation has to be scattered twice before entering the protected area.
The control booth will be large enough to adequately protect the controls and operator. The viewing window shall be at
least 16 by 24 inches. For standing operations, the bottom of the viewing window should be 45 inches above the floor.
There shall be a minimum of 18 inches from the edge of the shield to the edge of the viewing window.
b. Diagnostic and therapy installations. Guidelines for the thicknesses of barriers (walls, ceilings, and floor) shall be
determined from NCRP Report 49 and TB MED 521.
(1) Photofluorographic equipment uses a camera to photograph the image produced on a fluorographic screen.
When the x-ray tube orientation is restricted so that the useful beam can be directed only toward the camera, a primary
protective barrier is required only for the wall behind the camera. This primary protective barrier will extend at least 1 foot
beyond the perimeter of the useful beam at the wall. All other wall, floor, and ceiling areas of photofluorographic and
automatic upright chest installations are secondary barriers and should have a lead equivalent thickness of at least 1/32
inch.
(2) Floors will be covered with lead if the area below the radiography room can be occupied.
(3) Ceilings will be covered with lead if the area above the radiography room can be occupied.
8. Materials and installations.
Material used in protective barriers will conform to NCRP Reports 35 and 49. Lead is generally used as a shielding
material in facilities using x-ray potentials of 300 kilovolts and less. For higher voltages, standard concrete (140 to 160 lb-
3
3
ft ), Hi-Density concrete (190 to 340 lb-ft ) and earth are normally used. Lead sheets of different thicknesses can be
1-2
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