Special Considerations

Activated shielding and source components: Walls, shielding, and source components may become radioactive by the process of activation in facilities with high-energy radiation sources. The extent and magnitude of the activation is dependent on many factors including source “energy” and “on time.” In many cases activation occurs but is not a significant concern, since the radioactive materials produced have very short half-lives. The extent and magnitude of activation should be evaluated for sources with energies greater than 10 MeV. When appropriate, such facilities should be designed such that activated materials may be removed easily.


UC Practice


Exhaust ducts and collectors shall be located and/or shielded such that personnel exposures, along their route of travel and at the collector, are ALARA and do not exceed regulatory limits. Collectors shall be equipped with bag-in/out capability and located such that there is adequate space to change out collectors without contaminating uncontrolled areas and with minimum disruption of uncontrolled operations. Since such ducting and associated collectors are often located in uncontrolled areas occupied by individuals who are unfamiliar with radiation, even small exposures may be alarming to the occupants; therefore, it may be advisable to design shielding to reduce exposures far below regulatory limits or to provide additional training to the occupants regarding the effects of radiation.


UC Practice


Radiation source transport systems ("rabbits") shall be routed and/or shielded such that exposure limits are not exceeded in controlled or uncontrolled areas during routine operations or emergency situations (e.g., stuck source). To plan for emergency situations, an accident analysis shall be conducted and an emergency response plan prepared that will deal with any hazardous conditions that were identified.


Height and extent of shielding: For most single-floor facilities with machines with energies less than 150 kVp, shielding shall be 7-feet high. In multi-floor/level facilities, shielding in walls may need to be higher than 7 feet. For single-floor facilities with high-energy sources that can produce “skyshine,” shielding should extend to the ceiling, and the ceilings themselves may require shielding.




Nails/screws penetrating shielding material do not need to be capped with lead in walls that require less than 4 lbs/ft2 of lead.


UC Practice


Operator protection: Source controls shall be located such that no first scattered radiation reaches the control area (an exception to this general rule applies to DEXA bone density, and veterinary and dental units) and that exposures from primary and secondary radiation will not exceed regulatory limits when use and occupancy factors are taken into account.


UC Practice

17 CCR 30311(b)(2) and 30314(b)(2)


Shielding required to protect unexposed film or emulsions stored in areas near radiation sources shall be evaluated on an individual basis. The shielding required to protect personnel from radiation is often inadequate to protect unexposed film or emulsions stored near radiation sources.


UC Practice


Design to physically support shielding (e.g., weight, “cold flow”): The structure of the facility shall be designed (evaluated and updated for renovated facilities) to support required shielding. It is important to recognize that some shielding materials (e.g., lead) can “cold flow” with time (particularly for tall and thick sections). It is necessary to support shielding in a way that will address this problem or to use an alternative shielding material (e.g., iron, concrete).


Design to physically support the equipment: Some radiation sources and associated shielding are extremely heavy, so the structure of the facility may need to be specially designed (evaluated and updated for renovated facilities) to support it.


Seismic considerations: In California, shielding and equipment shall be designed and installed to meet seismic-restraint requirements.


State and local building requirements


Hazards associated with moving: Heavy shields, and high-voltage and high- magnetic fields are often present around radiation sources. Often, special administrative and engineering controls are required to deal with these hazards safely.


29 CFR 1910



Exhaust systems for hazardous materials (e.g., ozone, cryogens, gaseous activation products) produced or present around radiation sources: Exhaust systems need to be designed to maintain exposure levels for hazardous materials below the respective occupational exposure limits. Care shall be exercised in selecting the discharge points for these exhaust systems.


29 CFR 1910


ACGIH Industrial Ventilation, a Manual of Recommended Practice, latest edition


Interlocks: Often required on access doors to radiation sources or on required shielding components that are movable. The interlocks are required to disable the production of radiation if doors are not closed or if shielding is not positioned as required to provide adequate protection to controlled or uncontrolled areas. Such interlocks shall be fail-safe and tamper-resistant.


Emergency “Off” (mushroom) switches: Typically required in areas where exposures to individuals could exceed the limits established by the RSO and/or RSC if administrative or engineering controls should fail. Such switches shall be centrally located and in sufficient number so each potential user has convenient access.


Warning lights, audible signals, and signs: Warning lights and audible signals shall be in compliance with the requirements in 10 CFR 20.1601. Signage shall be in compliance with the requirements in 10 CFR 20.1902. Exceptions for the “High Radiation Areas” caused by radiographic and fluoroscopic machines used solely in the healing arts are specified in 17 CCR 30305 (c) (which requires a “Caution X-Ray” sign in the areas or rooms that contain permanently installed x-ray machines as the only source of radiation). These sources used exclusively in the healing arts are exempt from the controls of 10 CFR 20.1601 if they are in compliance with 24 CCR, Chapter 31C, Sections 3101C–3104C.


10 CFR 20.1601

10 CFR 20.1902

17 CCR 30305 (c)

17 CCR 30305 (d)

24 CCR 3101C- 3104C


Radiation area monitors: Typically required when exposure rates are such that the exposure of an individual in the area could exceed institutional administrative controls specified by the facility RSO and/or the RSC.