VIII. CAMPUS AND MEDICAL CENTER ACCELERATOR FACILITIES

The particle accelerator facilities on campus, which include the Triangle Universities Nuclear Laboratory (TUNL), the Free Electron Laser Laboratory (FELL) and the Medical Center Positron Emission Tomography (PET) Cyclotron Facility, present special issues in regard to radiation safety. The potential for high external radiation fields and the large amounts of radioactive byproducts during operation of these machines require a high level of awareness of the potential hazards.

This section provides information on some general radiation safety considerations associated with the accelerator facilities. Detailed information on the specific radiation safety-related policies for each facility is provided in the Radiation Safety Manual for that facility.

The principal radiation hazards in accelerator facilities are related to personnel exposure to the direct beam or secondary radiation, exposure to tritium contamination in the beam lines, and exposure to radioactivity induced in accelerator components by the primary beam or neutron activation.

  1. DIRECT BEAM AND SECONDARY RADIATION

    2. Personnel exposure to the direct particle beam or secondary radiation emitted from bombarded targets shall not be permitted. The Authorized User and/or Radiation Safety Manager shall provide instruction to all employees regarding:

    1. Proper alert procedures prior to accelerator startup;
    2. Audible and visible alarms indicating that the potential for beam activation is present;
    3. Exit routes from the accelerator vault and research areas;
    4. Methods to disable activation of the particle beam from within the accelerator vault research areas in the event the beam is introduced into the area.

  2. ACCELERATOR COMPONENTS

    3. Components of the accelerator can become radioactive during the course of operation due to neutron activation or interaction with the direct particle beam. The radioactive species produced in this manner depend upon the particle being accelerated, the energy of the particles and the materials present in the components, including impurities. Short- or long-lived radioisotopes may be present. For example, impurities in aluminum components may be activated to Co-56 by a proton beam or to At-211 (an alpha emitter) by an He-4 beam. Stainless steel screws or other parts not in the direct beam may be neutron-activated to Co-57. Components that may become activated include the beam line (including rubber O-ring seals), parts of the target assembly other than the target itself, the accelerator vacuum tank interior, bending and steering magnets, electrostatic deflectors, and the ion source.

    Users should take the following general precautions when approaching components of the accelerator:

    1. Items must be surveyed prior to handling. Radioactive components should then be handled according to each accelerators internal policy.
    2. When handling components that have come in contact with beam, proper personal protective equipment (PPE) shall be worn and properly disposed of.

  3. MACHINING OF RADIOACTIVE COMPONENTS

    4. Components with surface activities of certain exposure rates or contamination levels will not be machined. Consult local manuals for these levels. However, if components below these levels are to be machined, the following precautions must be taken:

    1. Survey the component and record the data before starting any process.
    2. Control contamination of machines, tools, and bench tops by controlling the debris from machining operations by spreading cover materials over the work area and floor to collect machined particles. Cutting oils or water must be used to control particulates. Electrically operated burnishing tools are not to be used on radioactive parts.
    3. After completion of the machining process, the debris must be surveyed and any radioactive waste must be bagged, labeled and disposed of appropriately.
    4. All tools, including machine tools and their parts (drill bits, band saw blades, taps, dies, drill keys, files, etc.), must be surveyed to verify that contamination has not occurred. If no contamination is found, they may be put back into regular service, but if contamination is found, tools shall be decontaminated appropriately. Wipes, rags, etc. used for decontamination must be surveyed for contamination and properly disposed of. Sandpaper and other abrasives must also be surveyed and properly disposed of.

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