Practical Controls

Control of External Radiation Exposure

External radiation exposure is primarily a problem related to high-energy beta and gamma emitters, and x-ray sources. There are several ways to reduce the exposure from external radiation sources. Some methods may be more appropriate in your particular situation than others.

Time - Reduce the amount of time you spend in close proximity to a radioactive source by working quickly and efficiently. However, do not work so fast that you will compromise your results or cause spills. If possible, take time to plan your work and perform dry runs. This will make you more familiar with the required experimental procedures and thereby lower the time required to work with the radioactive source. Do not loiter in the vicinity of radioactive sources.

Distance - Whenever possible, increase the distance between you and the source of radiation. Remember, the intensity of radiation exposure decreases with the square of the distance from the source, so if you double your distance from a source, the radiation exposure rate will be decreased to one-fourth of the initial value.

Shielding - Check your work area using an appropriate survey meter to determine if shielding is required. If you are using ³²P or other high-energy beta emitters, you should consider using shielding if a G-M survey meter reads about 10 times background. As previously discussed, approximately 1 cm of lucite can provide adequate shielding for most high-energy beta emitters. Shielding is not required for low energy beta emitters such as ³⁵S or ¹⁴C since these betas have a very limited range in air.

Adequate shielding for low energy gamma emitters, such as ¹²⁵I, can be provided by thin sheets of lead foil. Medium energy gamma emitters, such as ⁵⁷Co, often require about one-fourth inch (6.4 mm) of lead and high energy gamma emitters such as ⁶⁰Co, ²²Na, ⁵⁴Mn, ⁵¹Cr, and ¹³¹I may require several inches of lead to effectively attenuate the gamma radiation. Use Table 1 to determine the actual amount of lead shielding needed for your particular application.

When planning shielding, make sure to shield the source in such a way as to protect those individuals who may be on the other side of adjoining walls or lab benches. Notify the Office of Radiation Safety if you need assistance to measure exposure rates, determine shielding requirements, or require additional information.

Personnel Monitoring: Film Badges & TLDs - If you work with gamma or high-energy beta emitters, you will usually be issued a personnel dosimeter (e.g., film badge or TLD) to measure radiation exposure. Film badges and TLDs are used to record your exposure to external sources of radiation. A film badge contains a small piece of film and several different types of filters. These filters help to identify the type and energy of radiation producing the exposure.

Finger Ring Monitor - If you work with certain radiation-producing machines or millicurie quantities of high-energy beta or gamma radiation, you may be issued a finger ring to measure hand exposure.

Specialized Monitors - Individuals working in certain areas or under special circumstances (e.g., pregnant workers or around accelerators) may require specialized monitoring. Details of this special monitoring can be arranged through the Office of Radiation Safety.

Personnel radiation monitors are exchanged each week, month, or quarter, depending on the potential for exposure in the particular work area. The exposure recorded by each radiation monitor is reported to the user.

You can do several things to improve the accuracy of your radiation exposure record:

• Wear your dosimeter any time you work with or are near radioactive materials or radiation-producing machines.
• Wear your film badge on the collar or belt. If you wear a leaded apron during work, wear the badge on the outside of the apron on or near the collar. Ring dosimeters should be worn with the sensitive element (white portion) facing the most likely source of radiation. This element should be turned toward the palm when handling radioactive materials.
• Return dosimeters to the Office of Radiation Safety or your location coordinator promptly each time a new one is issued.
• Do not take your dosimeter home. Store it in a cool, dry place away from radiation sources.
• Notify the Office of Radiation Safety if you accidentally expose your dosimeter to radiation other than on the job.
• Do not wear your dosimeter when you have a medical treatment involving radiation and/or radiopharmaceuticals.
• When you terminate your work assignment involving radiation at LLU/LLUMC, please return your dosimeter(s) to your location coordinator or to the Office of Radiation Safety on the last day of your employment.

Control of Internal Radiation Exposure

Internal deposition of radioactive materials within the body may cause high doses to body organs. This is most significant when a radioisotope has a long residence time (effective half-life) in the body and/or selectively accumulates in specific body organ(s).

When attempting to control internal radiation exposure, it is helpful to know that there are four primary routes of entry into the body. These are inhalation, ingestion, absorption through the skin, and injection via cuts, etc. Methods to prevent internal radiation exposure seek to prevent the entrance of radioactive materials into the body via any of these routes.

Inhalation is the means whereby radioactive materials that are volatile or in a particulate form (e.g., dusts) enter the body. Specific examples include radioiodines, some forms of tritium and fine particulates such as labeled microspheres.

The most effective and straightforward means of eliminating the potential hazards related to inhalation are to perform all work with volatile compounds or fine particulates in a fume hood or glove box. To work properly, a fume hood must allow airflow through the hood face and into the exhaust system. Clutter in the hood and excessive face velocities (the optimal face velocity is about 100 lineal feet per minute), can greatly reduce overall hood efficiency. Effectiveness can be increased by moving the radioactive source further into the fume hood, checking that the fume hood sash level is not opened to more than the maximum allowed as indicated, that the air flow indicator is working properly, and by verifying that the fume hood air velocity has been checked within the last year. If a fume hood needs to be checked or if there are questions, call the Office of Radiation Safety. If your fume hood malfunctions, stop work and notify Campus Engineering. Remember, do not put your head into the fume hood during work.

Ingestion of radioisotopes is most likely to occur when radioactive materials are transferred from a source to the hands and then to the mouth. Radioisotopes also enter the body by absorption through the skin, and injection through cuts or abrasions. Absorption is an especially important route of entry into the body for radioactive iodine and some forms of tritium. Aseptic techniques and common-sense lab practices can prevent most internal intakes of radioisotopes by ingestion and absorption. Some important lab practices are listed below which will reduce the chance of internal exposure due to ingestion and absorption:

• Food and drink must not be stored or consumed in a laboratory.
• Make-up should not be applied while working in laboratory areas.
• Smoking is not allowed in laboratory areas.
• Wear proper protective clothing at all times when working with radioisotopes. This consists of a lab coat or apron, gloves (2 pairs when working with iodine, tritium, or high concentrations of other isotopes), safety glasses, and enclosed shoes.
• Perform radiation surveys of your work area and promptly decontaminate "hot spots".
• Monitor your clothing and body for radioactive contamination frequently and at the end of each workday.
• Wash your hands thoroughly with soap and water after working with radioisotopes, and before leaving the laboratory.

If you have reason to suspect that you have had an intake of radioactive material, notify the Office of Radiation Safety immediately.

Bioassay Program - A bioassay is a procedure used to determine the activity of a radioisotope contained in the body. One example is the bioassay for radioactive iodine. Since about 30 percent of the total activity of iodine that is ingested, absorbed, etc., during an iodine exposure is accumulated in the thyroid gland, the total iodine uptake can be determined by placing a calibrated scintillation detector on the neck directly over the thyroid gland and measuring the activity. Bioassays for other types of radioisotopes involve a urine assay. For this type of test, a urine sample is submitted to the Office of Radiation Safety for analysis by the appropriate method.

 Previous | TOC | Next