Radioactive Materials - Monitoring Activities
Good work practices and frequent monitoring of work and storage areas are essential in order to minimize exposure to radiation. Monitoring activities consist of not only the detection and evaluation of radiation fields, but also the measurement of personal dose (see dosimetry), and detection of the presence of contamination or a leaking source. CNSC has set specific requirements for each of these activities. For this reason each area will be outlined in greater detail in the sections below.
- Contamination
- Dose Rate
- Leak Testing
- Radiation Detection
- Choosing the Appropriate Detector
- Contamination and Survey Meters (Registration and Calibration of)
- Using a Survey Meter
- Wipe Test Calculator
It is important to note that two types of radioactive contamination may be found: fixed and non-fixed (loose) contamination. Each of these have different requirements that must be met, and the following paragraphs will address both the nature of each form and associated requirements.
- Record of Contamination Monitoring
- Classification of Radionuclides and Associated Non-Fixed Contamination Criteria
- CNSC Posters: Radioisotpoe Safety - Monitoring for Radioactive Contamination
- Liquid Scintillation Counter- Overview
- Liquid Scintillation Detection Efficiencies for (Beckman)
- Liquid Scintillation Detection Efficiencies for (Packard and Wallac)
Fixed Contamination
Fixed contamination is defined as radioactive material found in a location for which it is not intentionally or naturally found and which can not be removed even after multiple cleansings. This may be a result of a spill/release in which activity (in total or in part) has become absorbed/adsorbed onto a surface. This may be due to the chemical properties of the radioactive material or the structure and composition of the material in/on to which the radioactive material has been absorbed/adsorbed.
As it is not possible to remove this radioactive material, one must ensure it is appropriately shielded to minimize personal exposure and wait until the material has decayed away. ORM must be informed of all fix contamination and the action taken.
Non-fixed (Loose) Contamination
The CNSC has set out criteria which defines the acceptable level of contamination based upon the classification of the radionuclides (provided below), and upon the nature of the area being monitored. Two specific types of area are defined:
- non-fixed contamination in all areas, rooms or enclosures where unsealed nuclear substances are used, or stored ( LAB AREAS ), and
- non-fixed contamination in all other areas ie., non lab areas, and packaging prior to disposal etc. (OTHER AREAS) .
Contamination level for selected classes of a radionuclide are listed below. These values must be averaged over an area not exceeding 100 cm2.
Non - Fixed Contamination |
Class A * radionuclides |
Class B * radionuclides |
Class C* radionuclides |
| in all areas, rooms or enclosures where unsealed nuclear substances are used, or stored | 3 Bq/cm2 | 30 Bq/cm2 | 300 Bq/cm2 |
| in all other areas and packaging prior to disposal | 0.3 Bq/cm2 | 3 Bq/cm2 | 30 Bq/cm2 |
* When using more than one radionuclide in a room, the radionuclide with the lowest contamination limit must be used to determine the limit (Class A, Class B or Class C) that applies.
A map of the area monitored in the laboratory must be kept. Monitoring results of the packages (upon receipt/prior to disposal), and specific sites must be kept for three years. To assist you in monitoring activities, ORM addresses this subject in training and has specific contamination monitoring videos available.
To compare the contamination criteria with specific radioisotopes the following table may be referenced "Classification of Radionuclides and Associated Non-Fixed (loose) Contamination Criteria".
| IN PRACTICAL TERMS:
As long as one can prove that the contamination criteria is met by applying the standard practice of defining contamination as twice the background readings, this convenient approach may continue to be used. Don't forget to record your background reading each time you monitor. As well, you must verify the battery reading to ensure the battery is not low, as this will effect your monitoring efficiency. |
The aim of keeping doses as low as reasonably possible (ALARA) is the fundamental principle in radiation safety. To demonstrate ALARA one can compare the dose rate that could exist, to that which did exist after the implementation of exposure management practices. These practices have the goal of reducing any potential dose received to a minimal value. This might be achieved by: changing experimental procedures or storage practices, reducing the amount of radioactivity used, increasing the shielding used or the distance between the source and the individual.
CNSC also requires that all storage areas be regularly monitored. This is to ensure that the dose rate existing in an occupied area outside the storage area (room or enclosure) does not exceed 2.5 uSv/hr. To meet this requirement additional shielding may be necessary, or the occupancy profile reviewed and modified.
Thus it is necessary to have, or have access to, a functional survey meter to determine the dose rate. Not only must it be functional, but CNSC requires it to be calibrated annually. In addition this calibration can only be undertaken by an approved CNSC agency. Contact ORM to obtain a list of approved agencies. As ORM must demonstrate to CNSC that this requirement is met, copies of the calibration certificate must be sent to them.
CNSC requires that all sealed sources containing 50 MBq or greater of radioactive material be monitored to assess the integrity of the material containing the source. By definition a sealed source provides a level of assurance that the radioactive material can not escape and result in contamination or an inadvertent exposure. Unfortunate due to age, use or damage the integrity of the housing material can be compromised resulting in a potential serious situation. In evaluating the risk verses the probability of an incident CNSC has set a graduated leak test frequency schedule taking into account when sources are in storage, incorporated into devices, or in use.
Frequency
The frequency of leak testing is as follows:
- immediately after an event which may have resulted in the sealed source or shielding being damaged;
- immediately before using a source that had been in storage for a period of 12 consecutive months or greater;
- every 6 months for sealed sources in use and not incorporated into a device;
- every 12 months for sealed sources incorporated into a device;
- every 24 months when a source is in storage
Procedures
It is the responsibility of the permit holder to ensure all the sealed sources in their possession that require leak testing are monitored at the designated frequency. CNSC requires that the leak testing procedures be approved by Commission, the sampling and measuring process to be completed within 10 days of the each other, and finally both procedures and the results recorded on dedicated forms (below). Depending upon your faculty and laboratory it may be possible to coordinate the leak test sampling and measuring with others permit holders to allow for a more effective and efficient process. In some circumstances this may not be possible due to the location of the laboratory, use scheduling of the source, or personal preference. As a result individual permit holders may elect to leak test their own sources independently. Regardless of the process, ORM must receive a copy of both the sampling and measuring certificate for addition to the permit holder's file. In addition, the permit holder must retain these records for 3 years. Additional information may be obtained by reviewing the radiations safety manual and by contacting ORM.
Reporting a Leaking Source
Should a source be found to be leaking 200 Bq or greater, the following action must be taken:
- discontinue the use of the sealed source or sealed source incorporated into a device,
- minimize the risk of contamination,
- immediately contact ORM, so that the appropriate reporting of the incident can occur to CNSC, and
- in consultation with ORM determine the remedial actions to be undertaken to minimize exposure to the radiation and to decontaminate where necessary.
Contamination and Survey Meters (Registration and Calibration)
A contamination meter is designed to detect the presence of radioactivity (cps, cpm), whereas a survey meter is designed to detect dose rate measurements (Sv/hr or mrem/hr). To ensure that each meter is appropriate and to assist in addressing the need for calibration (CNSC requires survey meters to be calibrated every year), the following information is required.
Calibration of Meters
CNSC requires all survey meters to be calibrated annual by a company which has been approved by CNSC. A list of approved agencies is available from ORM. In addition a copy of all calibration certificates must be sent to ORM to retain for CNSC's review.