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Radiation Protection Handout


Introduction:

Proper use of equipment, techniques and procedures allow the use of radioisotopes with minimal exposure to you and without extensive contamination of facilities and equipment. This training booklet discusses the components of a sound radiation protection program for your radioisotope laboratory.

Laboratory: Before it was converted to radioisotope use, it was a conventional chemical laboratory with adequate ventilation, a working fume hood, and polished, easily cleaned non-absorbing surfaces. The adjacent storage room also had adequate ventilation and easily cleaned non-absorbing surfaces. It has been equipped with a liquid scintillation counter and is used as a count room.

Samples are drawn in the hood and prepared on the adjacent bench. Radioactive wastes are collected in the container adjacent to the fume hood. Contaminated glassware is washed in the sink next to the fume hood. Counting samples are prepared on the bench on the right side of the laboratory and taken to the count room for counting. The remaining bench, sink and desk are used for non-radioactive work.

Hood:

Before beginning your work, check the hood to ensure that it is working properly. Fume hoods have a sticker summarizing annual contractor tests. Ventilation rates should be 100 to 125 linear feet per minute at 15 inches sash height. Fume hoods should be rechecked annually.

Marking:

All radioactive materials use areas, equipment and storage containers must be marked with the radiation symbol. Failure to mark radioactive materials with the radiation symbol is the most common cause of the spread of contamination. Check to ensure that the entrances to the radioisotope laboratory and count room have been posted with a “Caution – Radioactive Materials” sign.

Proper Attire:

The routine use of proper laboratory attire can prevent contamination of your skin or personal clothing. Proper attire is required if there is a possibility of contamination (such as when handling or in the vicinity of someone handling radioactive materials). You should wear the following whenever you are handling radioactive materials:

  1. A laboratory coat with sleeves long enough to cover the arms to the wrists, and long enough to cover the torso to the thighs should be worn. You should wear it with the closures fastened.
  2. Eye protection should be worn to protect the eyes from splashes of radioactive and other hazardous materials.
  3. Closed-toed shoes, long pants or a long dress should be worn to protect the feet and legs from splashes.
  4. Disposable gloves should be worn to protect the skin of the hands and wrists from contamination. Gloves are most effective if two pairs are worn at a time, with the outer pair changed frequently.
Contamination:

In any radioisotope laboratory, you should separate work areas into potentially contaminated and uncontaminated areas and maintain a clear distinction between the two areas. In this example, the hood and adjacent bench and sink areas have been set aside as potentially contaminated areas. The reminder of the radioisotope laboratory and the count room are maintained as uncontaminated areas.

The potentially contaminated area includes (1) the hood, (2) the “hot” sink, (3) the “hot” bench, (4) the counting sample preparation area, and the adjacent floor areas. These areas are basic radioisotope work areas. Except for counting samples, radioactive materials are exclusively stored and handled within this area. Restricting the use of radioactive materials to these areas minimizes the spread of contamination within the laboratory, minimizes radiological control requirements, and allows other activities to occur in the non-contaminated areas.

There are two types of radioactive contamination – fixed and removable. Removable contamination is contamination deposited on the surface of structures, areas, objects or personnel that can readily be picked up or wiped up by physical or mechanical means during the course of a survey or during decontamination efforts. Fixed contamination is contamination adhering to the surface of structures, areas, objects or personnel not readily picked up or wiped up by physical or mechanical means during the course of a survey or during decontamination efforts.

Bench Coverings and Containment Trays:

You should cover the bench and other work areas with absorbent coverings to confine contamination. Use plastic backed disposable paper taped in place with the plastic side down. You should also place trays lined with plastic-backed absorbent material in the hood, on the “hot” bench and counting sample preparation area, and under the radioactive waste container. These shallow trays contain spilled radioactive materials. Label the trays and absorbent materials with “Caution – Radioactive Materials” stickers or tape. Replace the covering whenever it becomes damaged (worn, soiled, or torn) or contaminated.

Labeling:

Each sample vial or other radioactive materials bearing container should be labeled with the radiation symbol, name of the radioisotope, its activity, when the activity was determined and the chemical form of the material. Failure to label radioactive waste containers could lead to radioactive materials being thrown into the trash.

Double Containment:

If you are storing radioactive materials bearing liquids, you should use secondary containers of sufficient volume to contain all of the liquid should a spill occur.

Disposable Items:

You should use disposable plastic pipette tips, petri dishes, centrifuge tubes, etc. This routine practice prevents the need for decontamination of glassware.

Appropriate Handling Tools:

Handling tools serve dual purposes, reducing hand contamination while reducing extremity dose (includes tweezers, forceps, tongs, and shielded containers).

Personal Habits:

You should refrain from any eating, drinking and use of cosmetics in areas where radioactive materials are used or stored. Foodstuffs cannot be stored in refrigerators or freezers used for radioactive materials storage.

Surveys:

A survey is an evaluation of the hazards due to the presence of radiation and/or radioactivity under a given set of circumstances. Users shall perform contamination surveys and document the results in appropriate units for all areas where radioactive materials are used or stored under their supervision. Radioactive contamination is deposition of radioactive material in any place where it is not desired, and particularly in any place where its presence may be harmful. The harm caused may be excessive exposure to personnel or damage to the validity of an experiment or a procedure. Frequency: Monthly surveys should be performed in all laboratories. Post-experiment surveys may be used instead of weekly surveys should quantities greater than 250 µCi be used infrequently. Where less than 250 µCi are used or handled at any one time monthly surveys should be completed. Monthly surveys require both direct meter probes with an appropriate, calibrated survey meter and wipe tests performed for removable contamination.

Survey Procedure:

Laboratory surveys require the use of a calibrated survey meter with an appropriate detector as well as a wipe test for removable contamination. Wipe tests are to be counted using either liquid scintillation counting (H-3, C-14, P-32, S-35, etc.) or gamma counting (Cr-51, Fe-59, I-125, etc.,) depending on the isotopes your laboratory utilizes. If you are not sure which technique is correct contact the Radiation Safety Office.

You should make a drawing of the survey region for indicating locations of meter surveys and wipe tests. You will need an appropriate meter with documentation indicating the calibration date and efficiency for isotopes of interest and the normal background reading. You will also need material for performing the wipe test such as cotton swabs, tissue or filter papers or pieces of linen, vials in which to place the wipes and tweezers to allow handling the wipes without cross-contaminating the samples.

When working with isotopes other than tritium, it is necessary to have a portable survey instrument on hand to monitor exposure levels and check for contamination. A thin-window Geiger-type survey meter is appropriate for work with beta emitters (including Carbon-14 and Sulfur-35). Iodine-125 monitoring requires use of an Iodine-125 specific scintillation-type detector.

With the exception of tritium, virtually all beta and gamma emitters can be "seen" with a Geiger-Mueller (GM) detector survey instrument. This instrument can be used to determine the rough location and gross nature of contamination. The appropriate method is to position the probe surface 1 to 2 cm. above the suspected surface and then slowly scan the area, listening for variation in the click rate. In general, the meter should be shielded from high background to check for equipment or personnel contamination. Bench or floor surfaces should be checked directly and by wiping, then monitoring the wipe.

When you are ready, you should survey the laboratory thoroughly with the portable meter, concentrating on regions were radioactive materials have been used. Do not overlook areas where technicians may inadvertently walk or items that they may touch. Hold the detector as close to the surface as possible without touching to avoid contaminating the detector. Move slowly and deliberately along lab benches, near selected floor regions, radioactive material work areas, all small equipment, sinks, refrigerators, telephones, light switches and doorknobs. Pay close attention to lab coats, waste areas and containers for both radioactive and ordinary trash.

Record areas on the survey drawing which show counts 2 times background. Mark the location and give the highest count rate in the region and some description of the type of area--bench top, floor, etc. Indicate if the location is a radioactive material work area or if it was apparently contaminated inadvertently. Record areas and readings around all waste containers and radioactive materials storage areas.

Wipe monitoring can be used with all radioisotopes, and is the only reliable method for quantitative determination of removable contamination levels. The method involves wiping the surface with an absorbent medium (paper wipes) and then counting the wipes by Liquid Scintillation Counter (LSC) analysis. A background (uncontaminated) wipe is counted as a comparison control.

A LSC is a counter in which light flashes produced in a liquid scintillation solution by ionizing radiation are converted into electrical pulses by a photomultiplier tube. The number of light pulses produced and counted is proportional to the radioactivity in the solution.

When using lower-energy emitters (tritium, Carbon-14, Sulfur-35, or Iodine-125), surfaces should be checked with dry or damp pieces of filter paper or cotton swabs that are counted by liquid scintillation. You should examine floor in front of the work area, equipment (heaters, stirrers, tubing), and any items handled with work gloves during the experiment (faucet handles, drawer handles, etc.). If extensive or high-level surface contamination (3 times background or >220 DPM/100 cm2) is detected, clean the area with No Count Radioactive Cleaner and contact the Radiation Safety Office.