Radiological surveys of sufficient scope must be performed in all spaces approved for radioactive material use. Surveys ensure that radioactive materials are controlled and confined to limit the risk of unintended exposure to lab workers or members of the general public. This paper serves as a resource to all permit holders and radioactive material users who are required to perform surveys. Please contact the Office of Radiation Safety (ORS) if you have any questions regarding the guidance below.
The scope of performance and documentation of radiological surveys shall be commensurate with the risk posed in exposing workers or members of the public to ionizing radiation. The risk adjusted evaluation for the requirements is made at the discretion of the ORS and not solely a function of the material on hand in a particular laboratory. Criteria such as the experience of laboratory staff and enforcement history shall also be considered.
Training
All radioactive material users shall successfully complete Radiation Safety 101: Radiation Safety for Radiation Workers training course before being authorized to work with radioactive material and prior to performing laboratory surveys. This training is designed to ensure that the radiation worker will understand the purpose, practice, and interpretation of a radiation survey. This includes the following subject areas:
- Principles and practices of radiation protection;
- Radioactivity measurements, monitoring techniques, and using instruments;
- Mathematics and calculations basic to using and measuring radioactivity, and;
- Biological effects of radiation.
All radiation workers are expected to receive lab member provided on-the-job training tailored to the unique radiation requirements based on the use of their respective lab space and radioactive material research. The on-the-job training will include:
- Observing authorized personnel using survey equipment, collecting samples, and analyzing samples;
- Using survey equipment, collecting samples, and analyzing samples.
If the experience to provide this on-the-job training is no longer available in the research group, reach out to the ORS to request the necessary training to establish the survey program.
Detection Equipment
Equipment used in the performance of a laboratory survey may include portable survey meters or benchtop instruments. All samples and sources of radioactive material must be evaluated using an appropriate detection system for the radioactive material present and the type of survey being performed.
Benchtop Instruments
Benchtop Instruments for analyzing samples may include:
- A gamma counting system comprised of single or multi-channel analyzer to analyze samples which are expected to contain characteristic gamma or x-ray emissions;
- Liquid scintillation counting system to count alpha or beta decays;
- Efficiency must be known for all counting systems to convert counts per minute into units of activity such as disintegrations per minute. While liquid scintillation counters are often calibrated to convert H-3 and C-14 counts automatically into units of activity, this is not applicable to all isotopes or all instruments. The following conservative efficiencies are provided for common research isotopes:
|
Energy |
Counting Efficiency |
| Low (e.g., 3H) |
30% |
| Medium (e.g., 35S, 14C) | 50% |
| High Energy (e.g., 32P) | 70% |
Portable Survey Meters
Portable survey meters for surveying areas may include:
- A Geiger-Müeller based portable detector, calibrated in CPM, may be appropriate for some contamination surveys;
- A Geiger-Müeller based portable detector, calibrated in mR/hr, may be appropriate for some dose rate surveys depending on the spectrum of emissions and some contamination surveys;
- An ion chamber is appropriate for most dose rate surveys.
Detection equipment must be appropriate for the types of radioactive material which may be present within the research space being surveyed. For example, liquid scintillation counting is the only appropriate method for the detection of low energy pure beta emitting isotopes like 3H. Liquid scintillation counting may be the only viable option for detection of some gamma emitters if their characteristic gamma emissions have intensities too low to be detected. Contact ORS if unsure of the counting method or the appropriate efficiency.
Surveys
Dose Rate Survey
A dose rate survey should be performed anywhere workers are exposed to radiation levels that might result in radiation doses more than 10% of the occupational dose limits or where an individual is working in a dose rate of 2.5 mrem/hr or greater.
If exposure from radioactive material is a concern, dose rate surveys shall also ensure that the total effective dose equivalent to an individual member of the public is not able to exceed 100 mrem in a year and that the dose in any unrestricted area does not exceed 2 mrem in any one hour.
Work with ORS if you believe that your lab may be required to perform these types of surveys and you have questions.
Contamination Survey
Contamination surveys are required to be performed in sufficient areas to identify areas of radioactive contamination which may result in dose to workers or members of the public. Contamination surveys must seek to identify both fixed and removable contamination using appropriate detection equipment.
Contamination surveys should be performed:
- To evaluate the presence of radioactive material on unwanted surfaces including, but not limited to floors, laboratory furniture, and equipment;
- After a spill or contamination event;
- Post radioactive material use;
- After a change in the procedure or processes on which the radioactive material protocol is based;
- In unrestricted/public areas, in areas adjacent to restricted areas, and in all areas through which licensed materials are transferred or temporarily stored.
Below are the action levels for contamination surveys:
| Action Levels for Removable Surface Contamination | ||
| Area Description | Type of Emissions | |
| Betas & Gammas (DPM/100cm2) |
Alphas (DPM/100cm2) |
|
| Radiation Use Area | 2,000 | 200 |
| Non Radiation Use Area/ Unrestricted Area/ Public Area | 200 | 100 |
| Action Levels for Portable Survey Meter Results | |
| Instance | Results |
| Personal Contamination | Indistinguishable from background(1) |
| Surface Survey | 3x background at 1cm(2) |
Notes:
- Exceeding action levels for personal contamination during a meter survey requires immediate action consistent with section F in the ORS Emergency Procedures.
- Exceeding action levels for surfaces during a meter survey requires prompt wipe tests to evaluate levels of removable contamination.
Frequency
The frequency of surveys is not the same for all labs. Contact the health physicist assigned to your respective lab to get more specific guidance on minimum survey frequencies for your area(s).
A post-use surveys shall be performed at the end of each day, or after work with radioactive material has ceased for that day. Post-use surveys for unsealed alpha use labs shall be documented.
The frequency of routine contamination surveys shall be no less frequent than monthly. Certain permits that are considered to have an “elevated” risk may also be required to have a more frequent contamination survey requirement, (weekly, daily). A monthly survey requirement, as the name implies, are required for every room approved for unsealed radioactive material every calendar month in which unsealed radioactive material was used or stored in that room. Its recommended to schedule those at the start of each month to enable float should a delay occur. There should be a total of 12 surveys performed per calendar year at a minimum, with one occurring and dated for each month of the year.
No Possession Statement
The routine periodic contamination survey need not be performed if radioactive material has not been possessed and/or stored (e.g., no radioactive samples, no stock vials, no waste) in a laboratory since that laboratory was last surveyed. If radioactive material has not been possessed within the room(s) since the last routine periodic survey a “No Possession Statement” may be marked on the survey map with name and date of individual performing the evaluation. This is an optional selection on all survey diagrams/room maps provided by ORS.
Required Documentation
Completed surveys shall document the following information:
- A diagram of the area surveyed with indication of items and equipment surveyed;
- Annotations of specific locations on the diagram where wipes were taken;
- Background, ambient, and contamination radiation levels with appropriate units and locations, where appropriate (an area reading which fails to exceed background radiation levels must still be listed with a numerical value. The result should never list the word “Background” or “BKG”);
- Make/model/serial number/calibration date of instruments used;
- Name of the trained radiation worker performing the survey;
- Date the survey was performed.
Completed surveys must be retained for three years. One exception to this retention policy is for post-use surveys for most labs. While these surveys are required, they do not need to be documented and retained. Labs with requirements for post-use survey documentation and retention are notified of the expectation on a case-by-case basis.
Further Information
For further information on radiation surveys or the proper implementation please contact the ORS at RadiationSafety@wisc.edu or (608) 262-3600.
Please see the ORS website for more information: https://ehs.wisc.edu/labs-research/radiation-safety