Tham khảo tài liệu 'volume 17 - nondestructive evaluation and quality control part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | areas outside the facility. An unrestricted area is usually defined as an area where employees are not required to wear personal radiation-monitoring devices and where there is unrestricted access by either employees or the public. Second main work areas are shielded in accordance with applicable requirements. Some facilities must be inspected by an expert in radiation safety in order to qualify for licensing it is usually recommended that the owner consult an expert when planning a new facility or changes in an older facility to ensure that all local requirements are met. Appropriate shielding usually consists of lead or thick concrete on all sides of the main work area. The room in which the actual exposures are made is the most heavily shielded and may be lined on all sides with steel or lead. Particular attention is given to potential paths of leakage such as access doors and passthroughs and to seemingly unimportant paths of leakage such as the nails and screws that attach lead sheets to walls and doors. Third portable radiation sources are used in strict accordance with all regulations. In most cases safe operation is ensured by a combination of Movable shielding usually lead Restrictions on the intensity and direction of radiation emitted from the source during exposure Exclusion of all personnel from the immediate area during exposure The best protection is afforded by distance because radiation intensity decreases in proportion to the square of the distance from the source. As long as personnel stay far enough away from the source while an exposure is being made portable sources can be used with adequate safety. Finally access to radiographic work areas including field sites and radioactive-source storage areas must at all times be under the control of competent and properly trained radiographers. Radiographers must be responsible for admitting only approved personnel into restricted work areas and must ensure that each individual admitted to a restricted
