Radiation Exposure
Permissible doses
All unnecessary exposure to ionizing radiation is undesirable and exposure to such radiation fields should be limited to the lowest level reasonably achievable.
Individuals employed by TRU are not considered Atomic Radiation Workers; therefore permissible doses for members of the general public shall apply.
On the recommendation of a medical advisor and in the interest of an individual s health and safety, the AECB or designate may prescribe a lower permissible dose to that individual. If a female user becomes pregnant she must notify the RSO so that appropriate precautions may be taken to minimize radiation exposure.
In general, minimizing exposure to radiation may be accomplished by following a few basic rules.
- Minimize the time spent in the radiation field.
- Use appropriate shielding.
- Avoid any ingestion, inhalation or absorption of radioactive material through the skin. While small quantities of radioactive material may present an insignificant external hazard, once absorbed into the body they may collect selectively in one or more organs and present a much greater risk.
Personnel Monitoring
All users who in the course of their work are likely to receive a radiation dose in excess of 25% of the maximum permissible dose shall wear appropriate personal monitoring devices. Film badges or thermoluminescent dosimeters (TLDs) are supplied and evaluated by the Radiation Protection Bureau, Ottawa. Permanent records of findings from the Radiation Protection Bureau are maintained by the National Dose Registry of Health Canada in Ottawa. Records of exposures of TRU employees shall also be maintained by the RSO.
Personal monitoring devices should be worn at chest or waist height while working in the radioisotope lab. When not in use, these devices should be stored in areas where they will be protected from radiation and heat. A box will be provided outside the radioisotope lab.
TLD s are excellent dosimeters for X-rays, gamma radiation and bremsstrahlung from high energy beta emitters such as 32P, but do not detect radiation from low energy beta emitters such as tritium, 14C or 35S.
Individuals using 125I are required to undergo a thyroid scan quarterly and within three days following the experimental iodination of compounds.
Personal monitoring devices must not be exposed to sources of radiation unless being worn by the workers to which they have been issued, and should not be worn during non-occupational exposures such as during medical examinations.
Minimizing exposure
The maximum allowable radiation field for any working area is .025 Sv per hour (0.25 mR/h).
The radiation dose received by an individual is a function of: the length of time spent in the radiation field; the distance from the source; and the energy of the radiation emitted.
- Time
Minimize exposure time
The radiation dose an individual receives is directly proportional to the length of time spent in the radiation field. If possible, practice any new protocol with a non- radioactive blank. This should make you aware of any technical difficulties which would otherwise contribute to delays in handling. Familiarity with the procedure should also reduce the possibility of accidents.
- Distance
Maximize the distance between you and the source;
Distance is a very effective way to reduce the intensity of radiation incident on the body. Keep as much distance as possible between you and the radiation source. Use forceps or tongs to minimize radiation exposure to the hands when using stock vials which produce a significant radiation field.
The relationship between radiation dose and distance follows the inverse square law for point emission sources:
I1-=(D2)2 where I1 is the intensity of radiation at distance D1 from the source
I2 (D1)2 and I2 is the intensity at distance D1 from the source.
- Shielding
Use appropriate shielding.
When it is not possible during the course of a procedure to minimize the time and distance between the user and the radiation source, use of adequate shielding is necessary. Depending on the type and energy of the radioisotope in use, different shielding materials are recommended.
