Radiation Safety

OSLDs are assigned to a specific individual and cannot be shared by others. They are to be worn only while working at TMU and should not be taken off-campus. 

The badge  should be worn at the chest or waist level so you can accurately record whole body exposure. Extremity badges should be worn facing the source of radiation. If gloves are worn, the ring should be placed underneath the gloves to avoid potential contamination.

If you lose or damage your badge, please contact the radiation safety officer at ehs@torontomu.ca or 416-979-5000, ext. 554212 to replace it immediately.

Radiation badges have crystalline aluminum oxide elements which are sensitive to ultraviolet (UV) light and may produce false results if exposed. UV light is emitted from normal fluorescent lights and the badges must be protected from exposure to them. Care should be taken that the dose recorded by the badge is representative of the true dose to the individual to whom it is assigned.

OSLDs must not be left in an area where it could receive a radiation exposure when not worn by the individual (e.g. on a lab coat or near a radiation source). Store badges in a dark area with a low radiation background (i.e. in low light away from fluorescent or UV lights, heat and sunlight).

All monitoring results are maintained and evaluated by the radiation safety officer. Anyone who is interested in their radiation exposure or who has questions regarding the radiation dosimetry service may enquire with the radiation safety officer. Radiation monitoring results for each individual are recorded in the National Dose Registry operated by Health and Welfare Canada in Ottawa.

Whenever monitoring is being performed, standard lab practice for personal protective equipment (e.g. gloves, lab coat) are required. Radioactive contamination may be measured by one of two methods:

1. Direct use of portable instruments.
2. Indirect use of non-portable instruments (e.g. liquid scintillation counters, gas-flow proportional counters, gamma counters).

Contaminated areas must be cleaned without delay and should be verified by further contamination checks.

Monitoring for surface contamination is required to be done:

• at least weekly in a radioisotope work area;
• immediately after a spill or incident; and
• before equipment is released for non-radioactive use.

It is recommended that an active work area be surveyed at the end of each session to ensure that radioactive contamination is not inadvertently spread about or taken home. If no radioisotopes have been used since the previous survey, a notation of this can be made in the contamination survey form. No further action is necessary until the next usage.

A sketch of the floor plan for each room using unsealed nuclear substances should be prepared. The locations of active areas in the radioisotope work area should be numbered on the sketch. These locations should include bench tops, sinks, fume hoods, storage areas and non-active working surfaces such as floors, instruments and equipment, door handles, light switches, sink taps and telephone receivers. Several random locations should also be monitored. Keep the results of the monitoring in a log book.

Results from the contamination monitoring must be recorded on the  (google doc) Contamination Monitoring Sheet (external link) . If readings are below the action level for contamination, this finding may be noted in the form.

The readings from detection equipment can be related to regulatory criteria if the efficiency of the instrument for a specific radioisotope is known. The contamination criteria (expressed in Bq/cm2) will vary for different radionuclides. Refer to the  (google doc) Radiation Safety Manual (external link)  section 4.13 for contamination criteria for specific radionuclides. For mixtures of radioisotopes, complete all calculations using the radioisotope for which the instrument has the lowest detection efficiency.

Using the following equation, the amount of contamination can be calculated.

Removable activity =

Direct measurements involve using portable contamination monitor instruments to detect both fixed and removable decontamination. Contamination meters are specifically designed to measure radioactive contamination on a surface. The detector must have sufficient sensitivity to detect contamination at levels specified and outlined in the regulatory license issued by the Canadian Nuclear Safety Commission (CNSC), regulatory documents or internal requirements for the specific radionuclides being monitored. Depending upon the detector and the radioisotopes, direct measurement is often convenient for monitoring large areas. These meters may be used when background levels are negligible.

All radiation detection instruments must be registered with the radiation safety officer. New contamination meters should be tested to verify that they meet all specifications stated by the manufacturer. It is recommended that meters be calibrated annually and that records be kept for three years. To arrange for the calibration of meters, please contact the radiation safety officer.

Operational check

Before monitoring contamination, portable instruments should be given operational checks as specified by the manufacturer. Before each use, the operator should verify that a meter is functioning properly by checking for:

• battery power;
• high voltage; and
• source response time.

Measure background levels at a surface that is known to be clean.

Record the operational checks and background measurements. Any monitor not operating within the parameters of the operational checks or which show anomalous background measurements should not be used until their proper operation can be verified.

Meter placement

The reading from surface contamination monitors can be influenced by sources of radiation in the vicinity of the surface being monitored. If possible, remove all radiation sources from the area to be monitored by the survey instrument.

Monitor the locations marked on the plan of the working area by slowly passing the detector over each area. Keep the detector face towards the surface being monitored and keep the distance between the detector and the surface as small as possible without touching (and possibly contaminating) the detector. The window of the monitor must be uncovered when monitoring is occurring. If contamination is detected, stop and obtain a measurement. If a reading is off-scale, the monitor shall be moved to a distance where readings can be made, and the distance, reading and location noted.

Decontamination

If a reading greater than the contamination criterion is found, the area must be decontaminated. Clean the area and perform the monitoring again. Repeat the cleaning if monitoring indicates contamination. A reading in excess of the contamination criteria after repeated cleaning is an indication of fixed contamination or a high radiation background. Identify and mark the contaminated area on the plan. Record the highest measurement for each area and the final measurement after cleaning.

Indirect measurements detect removable contamination by means of wipe tests and non-portable detectors such as liquid scintillation counters. An indirect measurement of contamination is used when portable instruments are not sensitive enough for the radionuclides being monitored. For low-energy beta emitters such as Tritium (H-3), Sulphur 35 (S-35) or Carbon 14 (C-14), monitoring through the use of wipes and liquid scintillation counting is the most effective means for contamination monitoring. This type of measurement is also effective in areas with high radiation background. As with other detection equipment, the efficiency of the counter should be determined for the specific isotope being counted, prior to contamination monitoring.

Steps for monitoring contamination using wipes

1. Select an absorbent analytical grade of filter paper with a diameter of about five centimetres.
2. With the filter, wipe each of the locations shown on the plan of the working area. Hold the filter paper on the edge with your thumb and index finger. Use uniform and constant pressure to ensure the entire area is wiped. Wipe an area of approximately 100 cm² using an S-shaped pattern.
3. Use one numbered wipe per location.
4. Place the wipe in a scintillation vial, add scintillation fluid and cap the vial.
5. Count the wipes, for typically one to two minutes, in a low radiation background area and record all results. Include a blank wipe to determine the net count-rate above background and standard with each set of wipes. When using the wipe method of measurement, only a fraction of the contamination will be removed. As such, assume a wipe efficiency (i.e. collection factor) of 10 percent.
6. Record the wipe test measurements.
7. If contamination is found, these areas must be identified and decontaminated. After cleaning, wipe the area again and continue until the area has been cleaned.
8. Record the results before and after the decontamination including the printout from the liquid scintillation counter. Keep the printout from the counter with the contamination monitoring records.

Not all monitors are suitable for or sensitive enough to detect contamination from all types of radionuclides. Portable contamination monitors cannot be used to detect Tritium (H-3) and typically have very low efficiencies for other low-energy beta emitters such as Carbon 14 and Sulphur 35. The most effective method for surface contamination monitoring for these low-energy beta emitters is by using wipe tests and liquid scintillation counting.

High-energy beta emitters such as Phosphorus 32 or gamma emitters can be effectively monitored using a portable contamination monitor with an appropriate detector, (e.g. a Geiger–Müller (GM) pancake probe for high-energy betas).

Background radiation

The typical background readings (i.e. the naturally occurring radiation readings) should be known for the general area before monitoring begins in a radiation area. In this way, a valid comparison can be made of the radioactive area being monitored.

Meter efficiency

For each instrument, the detection efficiency (especially for contamination meters) should be known prior to monitoring. For contamination monitors, the detection efficiency will vary by isotope.

Efficiencies for all meters and scintillation or gamma counters must be obtained for those isotopes that will be used in the lab. The detection efficiency depends upon several factors including the type, size and shape of the detector (larger surface areas are more sensitive), the distance between the detector and the nuclear substance, type of radioisotope and type of radiation measurements, backscatter towards detector, and absorption by air of radiation before reaching the detector. Efficiencies can be obtained using a standard source with a known activity.

Maintenance

The permit holder is responsible for ensuring that radiation detection equipment is maintained. Portable meters will be examined by the radiation safety officer (RSO) during regular lab inspections. Any meter found to be functioning improperly will be removed by the RSO until the equipment is serviced and functioning. The RSO can assist in arranging repairs and required calibration services.

All radioactive waste is either shipped to AECL Waste Management Systems in Chalk River, Ontario for disposal or held for decay. All safety precautions required for the handling and storage of radioactive materials must also be observed with subsequently generated wastes.

All radioactive waste includes:

• surplus radioisotope material in any form (e.g. solid, liquid, sealed sources, devices);
• material that has come into direct contact with radioactive material (e.g. gloves, culture dishes, flasks, needles); and
• materials used for radioactive decontamination (e.g. paper towels, sponges).

• Radioactive waste must not be placed in non-radioactive waste containers.
• Additionally, non-radioactive waste should not be packaged with radioactive waste in order to reduce the amount of materials for nuclear disposal.
• All radioactive materials destined for waste disposal should be clearly marked while awaiting removal.

• Storage of radioactive waste must be clearly identified and secured in the lab.
• Radioactive waste should not be stored beneath any working area without adequate shielding and containment.

• No liquid containing radioactive materials shall be discharged to the lab drains.
• The permit holder must notify the radiation safety officer for disposal of all radioactive materials and devices.
• Liquid scintillation vials must be collected separately in the lab (i.e. placed in transparent plastic bags).
• There are very few companies that have the experience and required licenses to properly dispose of radioactive materials and sealed sources. The radiation safety officer will arrange for the removal and disposal of all radioactive waste and sources.

Note: Disposal of radioactive waste materials requires strict packaging and transport requirements. The radiation safety officer can assist researchers in properly transporting radioactive waste off-campus for disposal.