Exposure to radiation must be closely monitored to ensure that no one receives an exposure which could have a potentially adverse health effect. In recognition of this, CNSC has set dose limits for members of the general public and nuclear energy workers. The following table outlines those limits:
Dose limits Assigned By CNSC
|Body Part||Member of General public||Nuclear Energy Worker|
|Whole body,gonads,bone marrow||1 mSv||50 mSv|
|Skin,thyroid, bone||50 mSv||500 mSv|
|Tissues of hands,feet and forearm||50 mSv||500 mSv|
A nuclear energy worker is defined as any individual in the course of their work who would exceed the dose limit of a member of the general public. For an individual to be identified as a nuclear energy worker the following information will be assessed: research design, historical records and anticipated dose. If deemed as a nuclear energy worker the individual will be formally required to sign the appropriate documentation. It is important that ORM be informed of any change in experimental design that could result in an exposure above the general public limits.
The dosimeters used by the University can be thermoluminescent dosimeters (TLD) called Next Gen thermoluminescent or the newer, InLight Nova dosimeters which use optically stimulated luminescence (OSL) technology. The dosimeters can be whole body badges, wrist extremity badges or rings. All individuals who are exposed to radiation, and who may receive a dose will be issued a dosimeter. ORM may also elect to monitor (short or long term) individuals who do not directly work with radiation but may be in proximity to radioactive sources. These individuals include support staff, contractors, and trades personnel. The dosimetry requirements for authorized users are listed on the second page of the Internal Radioisotope Permit. The type of dosimeter is also listed on this page, i.e. whole body, extremity or ring badge. Note, CNSC requires a ring dosimeter to be worn by a person who handles a container whose content is 50 MBq or greater of phosphorous‐32, samarium 153, strontium 89, or Yttrium 90.
It is important to note that hydrogen‐3 and carbon‐14 emit such weak beta particles that they can not penetrate the shielding of the badge to be detected. The shielding incorporated into the dosimeter badge is intentionally designed to mimic the natural shielding provided by your skin, fat and other organs. Thus a dosimeter will not be assigned to those individuals who use these radioisotopes. Although the risk of external exposure is minimal, proper procedures must be followed to avoid an
internal exposure due to consumption, absorption etc..
CNSC has produced a poster to assist you in storing and wearing your dosimeter badge correctly. This poster can be found on the Radiation Safety Web site. CNSC Poster: Proper Care and Use of Personal Dosimeters
the dosimeter to register a non‐occupational exposure.
Dosimetry service to the University of Ottawa is provided by Health Canada's National Dosimetry Service (NDS). This service is registered and approved by CNSC. To enrol in the NDS the following information must be submitted: Name, Sex, Date of Birth, Place of Birth and Social Insurance Numbers. Individuals who register to work in a radioactive use laboratory and fill out the "New User Registration Form" will automatically be issued a dosimeter if required. For other non-users who wish to have a dosimeter, contact ORM and they will issue a badge if it is deemed necessary.
Through the NDS service, an individual's dose is tracked for life. An individual can change employers numerous times or even have a hiatus from a radiation related employment and his/her dose record will still follow the individual. Because of the number of individuals tracked in this system, the system requires social insurance numbers to ensure the doses are correctly assigned to the individuals
Dose records are sent to ORM every three months, where they are reviewed for any abnormal or atypical results. If an atypical dose is reported, ORM will notify you by email and follow‐up with you to determine if the exposure reading represents a personal dose due to experimental design, a singular incident, or a non‐personal dose due to storage practices or damage. ORM also monitors the readings to ensure an individual's dose does not exceed the CNSC dose limits. Should a reading approach the limit, the experimental design and your work scheduling will have to be reviewed and modified if necessary. Should you wish to see your acummulative dose, please feel free to contact ORM. For complete dose histories, contact Health Canada National Dose Resgistry and complete the Employee's Dose History Summary (EDHS) Request Form.
RadioIodine is a health risk since it can easily concentrate in the thyroid if the appropriate containment procedures are not used. In CNSC regulatory document RD‐58, the thyroid monitoring requirements are focused on volatile (unbound)radioiodine due to the high risk of this form to concentrate in the in the thyroid. Currently, the University of Ottawa`s Nuclear substance and Radiation Devices liicense 07152‐1‐23.0 does not differentiate between bound or unbound iodine and requires thyroid monitoring of individuals if they use a single 24 hour period more than 2 MBq (0.054 mCi) of iodine‐125 or iodine‐131 on the open room, more than 200 MBq (5.41 mCi) in a fume hood or more than 20 GBq (541 mCi) in a glove box. Thyroid monitoring is also required if individuals are involved in a spill of greater than 2 MBq or if an individual has external (skin) contamination. With the external (skin) contamination, no quantity of radioactivity (MBq) is specified and since there is no activity specified, procedures for thyroid monitoring must be in place for any use of I‐125 or I‐131.
For radioiodine Users that will use greater than 2 MBq in the open room, more than 200 MBq in a fumehood and more than 20 GBq in a glove box, a baseline thyroid reading will need to be taken before work is started. This is a “best practice” and not a regulatory requirement. Then thyroid monitoring is required between one and five days following the exposure.
For all users who are involved in a spill or have external (skin) contamination, contact ORM or Radiation Specialist immediately (email@example.com, ext. 3057 or 8081) and monitoring will be arranged between one and five days following the exposure.
If you plan to use I‐125 or Iodine‐131, contact ORM since a thyroid monitoring program will need to be re‐instated and purchases will not be approved until the program is established.
All users who plan to use radioiodine compounds should read the Safe Work Practices for Radioiodine which is in section 2.16.1 of this manual.
All workers at the University are considered to be members of the general public with regards to the maximum permissible radiation dose and as such, there is no difference between the maximum amounts or radioactivity a pregnant work can receive versus a non-pregnant worker.
However, individual must notify the Radiation Specialist and their permit holder/supervisor as soon as they suspect a pregnancy. If necessary, the Radiation Specialist will keep this information in confidence.
Depending on the exposure risk in the laboratory, the worker may be re-assigned tasks and offered participation in a special monthly dosimetry service. Any specific concerns should be brought to the attention of the Radiation Specialist or the supervisor.