External exposure is radiation that comes from somewhere outside the body and interacts with us. The source of radiation can be a piece of equipment that produces the radiation, like an x-ray machine, or it can be from radioactive materials in a container. The amount of external radiation exposure received is related to the distance from the source, the energy of the emitted radiation, the total amount of radioactive material present or the machine setting, and the time of exposure. Radiation workers can control and limit their exposure to penetrating radiation by taking advantage of time, distance, and shielding.
Reduce Time: By reducing the time of exposure to a radiation source, the dose to the worker is reduced in direct proportion with that time. Time directly influences the dose received: if you minimize the time spent near the source, the dose received is minimized. For example, if possible, interview a nuclear medicine patient before drug administration not after.
Increase distance: When appropriate, increase the distance between you and the radiation source (e.g., sealed source, x-ray tube). The exposure rate from a radiation source drops off by the inverse of the distance squared. For example, if a problem arises during a fluoroscopy procedure, stand on the image intensifier side of the C-arm if possible, or, when not assisting, step away from the patient if feasible.
Use shielding: The third exposure control is based on the proper radiation shields, automatic interlock devices, and in-place radiation monitoring instruments. Except for temporary or portable shields, protective drapes, lead or lead equivalent aprons, this type of control is usually built into the particular facility, such as concrete walls next to a radiation oncology accelerator. For portable x-ray devices, follow the vendor instructions.
In general, alpha, beta, gamma and x-ray radiation can be stopped by:
- Keeping the time of exposure to a minimum,
- Maintaining distance from the source,
- When appropriate, placing a shield between yourself and the source, and
- Protecting yourself against radioactive contamination by using proper protective clothing.