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14.1 Hazards of Radiation-generating Devices

Hazards of radiation-producing equipment are classified into beam hazards (primary) and scattered radiation (secondary). Adequate shielding must be used to protect against exposure to both primary and secondary radiation.

14.2 Sealed Sources

A sealed source is radioactive material permanently bonded or fixed in a capsule or matrix designed to prevent the release and dispersal of the radioactive material under the most severe conditions likely to be encountered in normal use and handling.

Sealed sources are used as external sources of radiation. Examples of sealed sources are 137Cs irradiators and small check sources used to make sure radiation detectors are operating properly.

Sealed sources containing more than 100 μCi of beta and/or gamma emitters and greater than 10 μCi of alpha emitters must be leak tested for removable contamination on the external surfaces of the source at least every six months by EH&S.

The sealed source must be removed from use if the leak test results show greater than 0.005 μCi of removable contamination on the external surfaces of the sealed source.

All sealed sources (containing more than 100 μCi beta and/or gamma emitters and greater than 10 μCi alpha emitters) purchased or owned by investigators must be registered with EH&S. EH&S will perform the leak tests and inventory every six months.

14.3 Rules for Safe Operation

  1. Only trained operators are permitted to use radiation-generating devices. Training must be provided by EH&S and documented prior to first use of any radiation-generating device.
  2. Radiation-generating devices include, but are not limited to, x-ray machines, fluoroscopy units, CT scanners, linear accelerators, and other devices that produce ionizing radiation as a result of their normal operation.
  3. Any facility having radiation-generating devices must be surveyed for possible exposure hazards to the operators. Register new equipment with the RSO prior to use.
  4. Radiation-generating devices must be surveyed during the initial operation of such equipment and whenever any change is made in the installation that might change the radiation level to which a person could be exposed. In evaluating the results of the survey, the actual operating conditions, including workload, use factor, occupancy and attenuation of the useful beam by patients or objects, must be the criteria for recommendations of changes.
  5. Dosimeters must be worn by operators or, if the equipment is capable of producing greater than five mrem in one hour, in an accessible area at a distance of thirty centimeters from the tube.
  6. A written record of all surveys will be presented to the individual responsible for each unit within one week, unless the survey indicates abnormal values, in which case the responsible individual must be informed immediately.

14.4 X-ray-producing Machines

There are many x-ray-producing machines at the Center used for various reasons. These machines include an x-ray diffraction unit used to analyze the structure of materials, a micro CT unit used to analyze mice and other small animals, a veterinary x-ray unit used to x-ray larger animals such as dogs, and a DEXA unit used in PHS studies. X-rays pose risks similar to those of gamma rays; therefore certain requirements must be met to ensure the machines are used properly and safely.

Annual inspections of x-ray equipment are required to ensure safe operation and compliance with all standards.

X-ray equipment operators must be trained in safe operating procedures for the machines they use and must be able to demonstrate competency. Additionally, all x-ray equipment operators must complete x-ray safety training provided by EHS.

Only a worker listed as an x-ray operator on an authorized PI's RMUA may operate x-ray-producing machines.

A PI who wishes to use an x-ray-producing machine must submit a RMUA or a RMUA amendment to the RSC requesting authorization for use.

Additional requirements of the x-ray safety program are detailed in the X-ray Safety Manual. Staff who wish to use x-ray-producing machines should refer to this manual. For a copy of this manual or additional information, contact the RSO.

14.5 Self-shielded Irradiators

Self-shielded irradiators within the Center are used to irradiate small samples. The irradiators each contain small sealed sources. A worker must be on a PI's RMUA, complete irradiator training, and meet access requirements prior to being allowed access to use an irradiator. For details on access requirements, contact the RSO.

The gamma radiation emitted produces ionization within the material being irradiated. The radiation does not cause or induce radioactivity; that is, the material being irradiated does not become radioactive itself.

Irradiators are adequately shielded with lead. The dose rate around the outside of the irradiators does not exceed 0.1 mR/hr at 30 cm from sides. It should be kept in mind that even a small dose rate of 0.1 mR/hr can register several thousand cpm on a portable radiation detector.

The irradiators are very easy to use. Please observe the following safety precautions:

  1. It is good practice not to lean against the irradiator while samples are being irradiated.
  2. Materials that are basically unstable, explosive or highly exothermic, should notbe irradiated in the unit.
  3. Samples should be centered in the chamber for uniform exposure.
  4. Use beakers or flat-bottomed containers to hold samples.
  5. Test tubes or conical vials should be inserted into a holder so they are supported in an upright position.

14.6 Malfunction of Radiation-producing Machinery

Radiation-producing machinery includes x-ray machines, linear accelerators, irradiators, and similar devices designed to produce ionizing radiation. There are specific requirements for operating such machines, including a requirement that all safety alarms and interlocks be working correctly at all times. In the event of any malfunction in any radiation-producing device or related safety systems, the following actions must be taken:

  1. Exit the room containing the device immediately.
  2. Contact the RSO during normal hours; contact Security after hours, on holidays, or on weekends.
  3. Attempt to determine whether the device is emitting radiation.
  4. If the device is emitting radiation, attempt to disable or secure it without entering the room in which the device is located.
  5. Monitor radiation levels near the room housing the device with an appropriate instrument.
  6. Lock doors, post a warning sign, and have the area guarded at a known safe distance to ensure against accidental exposure.

14.7 Gas Chromatography Equipment

Some types of gas chromatography equipment contain small radioactive sources. These sources are usually 3H or 63Ni electroplated onto metal inside an electron capture device.

If you own or intend to buy gas chromatography equipment containing radioactive material, notify EH&S. The equipment must be added to your RMUA and checked every six months for leakage.

Gas chromatography equipment containing 3H releases a small amount of 3H during normal use. Operating at an excessive temperature may cause large releases from both 3H and 63Ni devices. Therefore, all gas chromatography equipment containing radioactive material must be exhausted through tubing either into a chemical fume hood, out a window, or through a manufacturer's approved trap.

Dismantling these devices for cleaning could release some of the radioactive material, therefore precautions should be taken to prevent exposure.

If the GC is moved, inform the EH&S of the new location. Do not dispose or transfer the device to any other user or facility without notification of the RSO.

14.8 Electron Microscopes

Electron microscopes produce x-rays internally. These x-rays are produced when scattered electrons from the primary electron beam strike metal parts within the microscope. The x-rays usually escape through weak points in the equipment, such as between the gasket-sealed junction of two sections of the column, or at the top of the scope where the electrical cables are attached to the gun. Newer electron microscopes are adequately shielded so none of these x-rays should escape the microscope.

After installing or moving an electron microscope, or after making significant modifications such as installing new detectors on ports in the specimen chamber, it is good practice to check the microscope using a radiation detector with a NaI probe.

With the radiation detector, check the gun, column and specimen chamber while the machine is operating at its highest accelerating voltage. Any radiation escaping the column or the specimen chamber must be stopped either by shielding, or preferably, by repair.

EH&S will perform these checks when requested.

Radioactive chemicals used as tracers or stains in electron microscopy are additional sources of ionizing radiation. Uranium and depleted uranium, often used as uranyl acetate, is a good stain by virtue of its heavy metal electron-scattering properties. All uranium is radioactive, but to varying degrees. Any uranium can easily be detected using a radiation detector with a NaI or a GM probe. Uranium used in electron microscopy is only a hazard if inhaled or ingested, so wear gloves and use good lab techniques when using uranyl compounds.

Some samples may contain very small levels of radioactive material used as tracers. These samples contain such small amounts of radioactive material that they do not pose an external radiation hazard. The samples may be an internal hazard if ingested or inhaled, therefore gloves and good lab techniques should be used when working with all samples.

Consult with EH&S for ways to check for contamination and to dispose of the uranium waste.