Table 6-27. Occupancy Factors (T).
Full Occupancy (T = 1)
X-Ray control space and waiting space, darkrooms, film reading areas, workrooms, shops, offices and corridors
large enough to hold desks, living quarters, children's play areas, occupied space in adjoining buildings.
Partial Worker Occupancy (X = ¼)
Worker restrooms, occupational use corridors too narrow for desks.
Partial Occupancy (X = 1/8)
Public corridors too narrow for desks, utility rooms, employee lounge.
Occasional Public Occupancy (T = 1/20)
Rest rooms or bathrooms, storage rooms, vending areas, outdoor areas with seating
Rare Occupancy (T=1/40)Outside areas used only for pedestrians or vehicular traffic, unattended parking lots,
attics or crawl spaces, stairways, unattended elevators, janitors closets.
* For use as a guide in planning shielding where adequate occupancy data are not available.
Direction of Useful Beam.
a. The cost of shielding may be reduced significantly by arranging the installation so that the useful beam
is directed toward occupied areas as little as possible. (There is, of course, no objection to directing the
useful beam at occupied areas provided there is adequate protection.)
b. Devices that permanently restrict the direction and cross section of the useful beam may reduce the area
requiring primary barriers.
Radiation Energy, Output and Workload.
The shielding for each occupied area shall be determined on the basis of the expected maximum kilovoltage or energy,
mA or Rhm, workload, use factor and occupancy factor affecting it. Consideration should be given to the possibility
that the values of these parameters may increase in the future. It may be more economical to provide a higher degree of
protection initially than to add to it later.
Structural Details of Protective Barriers.
Shielding for radiographic installations is normally provided by installation of sheet lead, or concrete. Facilities where
high workloads and gamma-ray sources are used may use a combination of these materials, or use concrete loaded with
a high iron content aggregate to improve shielding efficiency. The half-value layers of lead and concrete (the thickness
of each material necessary to reduce the exposure intensity by a factor of two) for various energy x-rays and gamma
rays is shown in Table 6-28.