Contamination control is the primary way to manage radiation risk in the laboratory. Prudent contamination control involves careful planning, containment of unsealed source material, use of protective coverings on work areas, use of personal protective equipment (PPE) and the avoidance of spills through training and experience. Contamination monitoring is an important element in assessing the effectiveness of contamination control program. There are three fundamental types of radiation monitoring procedures conducted at the NIH.
• Hand-held contamination survey meters are used to located fixed and removable contamination on surfaces, equipment, personnel and clothing, with result usually expressed in counts per minute (CPM).
• Swipe or smear sampling is used to locate and quantify removable contamination on surfaces and equipment with results usually expressed in counts per minute (cpm) or disintegrations per minute (dpm).
• Exposure-rate metering is used to measure the exposure rate in an area from contamination and stored source material, and is usually expressed in milliroentgen per hour (mR/hr).
Routine Contamination monitoring at the NIH is recorded and documented on a variety of contamination surveys as needed
A daily contamination survey is required each day unsealed radioactive material (RAM) is used. Daily contamination surveys are NOT required on days when work with RAM was not performed.
Hand-held radiation survey meters can be used as long as the sensitivity of the instrument allows for efficient detection of the radionuclides handled. Contamination monitoring should be performed on the ungloved hands, lab coat, work area, the floor adjacent to the work area, the top and bottom of shoes, waste storage areas and any potentially contaminated equipment.
· When using a hand-held survey meter, a count rate of greater than two times the background usually indicates the presence of contamination.
· Any area found to be contaminated must be decontaminated immediately and re-surveyed following appropriate decontamination procedures.
· Contaminated lab equipment that is dedicated for radioactive material work and likely to be re-contaminated should be appropriately labeled and kept separate from non-contaminated equipment.
For low-energy beta emitters radionuclides, such as tritium, a swipe or smear survey is required using a liquid scintillation counter (LSC) and appropriate counting settings. As indicated below, hand-held survey meters are not appropriate due to their extremely low monitoring efficiencies.
A thorough contamination survey of the lab module is REQUIRED every calendar month when unsealed forms of radioactive material are used since the last monthly survey. It is not required that the survey be performed on the exact day each month, but there should be a consistent pattern when the surveys are performed, e.g. during the third week of the month. Guidance on what constitutes a lab modules can be found in the guidelines on how to conduct and report monthly surveys using the NIH 88-12 form. A summary of how a monthly survey is to be conducted is given below.
A minimum of ten or smear sample locations must be collected, including at least two locations on the floor. Swipe or smear locations should include areas and equipment that have a higher potential for being contaminated, and locations should be varied from month to month. Suggested locations to perform swipe or smear sampling are:
• Work areas, lab benches, and desks
• At least two locations on the floor must be taken
• Floor adjacent to work areas and near hallway entrances
• Lab equipment used with radioactive materials
• Sinks in the laboratory
• Door handles of lab doors, incubators and radionuclide storage refrigerators and freezers
• Shelves in refrigerators and freezers
• Incubators shelves
Swipes or smears will be counted using an appropriate LSC or gamma counter using proper sample labeling techniques and counter settings.
Any contaminated location identified must be decontaminated and re-surveyed to demonstrate compliance with the removable contamination limits for restricted areas, as listed in the Surveying for Removable Contamination section below.
• A diagram of the laboratory
• The identification and activity of those radionuclides used during the month
• Locations of where swipes or smears were taken
• Description of contamination identified during the survey
• Description of re-survey results
A copy of the completed survey form must be submitted to the DRS along with a copy of the LSC or gamma counter printout. The original survey report must be kept on file in the laboratory Radiation Safety Records notebook or similar file. Reports are to be retained for a minimum of three years for review by the DRS or contract personnel and NRC inspectors.
If radioactive materials are not used during the calendar month, survey reports indicating no radioactive materials usage must be submitted electronically via the DRS Authorized User Portal. Contamination monitoring swipes or smears are not required if no radioactive materials were used.
Monthly Contractor Survey Service
Monthly surveys may be contracted to Clym Environmental Services (Clym), the DRS's regulatory compliance support contractor. There is a set cost per lab module that may be paid by CAN, credit card, or purchase order. Clym is the only contractor approved by the DRS to provide this and other DRS services.
To make arrangements for this service or for more information, contact Clym at 301-435-7953, 888-289-2324 or beth@clymenvironmental.com
Comprehensive or Contractor Surveys
In addition to daily and monthly surveys performed under the direction of the laboratory’s Authorized User, the DRS maintains a staff of contract technicians who perform routine comprehensive surveys of all posted laboratories. The purpose of these surveys is to ensure compliance with NRC regulations and NIH license requirements and frequency determined by the DRS and varies for each lab, i.e., semiannual, quarterly, bimonthly, monthly, or weekly, based on radionuclide usage and activity.
Like daily and monthly surveys, comprehensive surveys are designed to monitor for contamination. During these surveys, measurements of radiation levels, inspection of lab records, and an evaluation of general compliance with the NIH Radiation Safety Program are also performed.
Results of a comprehensive survey are reported to the DRS on a Radiation Survey Report or contractor survey report form and include any items of noncompliance. The Area Health Physicist reviews each comprehensive survey and determines if corrective action needs to be taken.
A copy of each comprehensive Radiation Survey Report is furnished to the Authorized User of the lab along with a set of Radiation Safety Survey Information Sheets
to describe the survey results and suggest corrective actions.
Surveying for Removable Contamination
Removable contamination is defined as the radioactivity that can be transferred from a surface by rubbing with moderate pressure. The swipe or smear test is used to assess the level of removable contamination and is the required method for monitoring radionuclides.
A small piece of cloth, filter paper, or fiberglass disk is used to wipe an object or sample location to determine the amount of removable contamination present. Fiberglass disks are preferable for low-energy beta emitting radionuclides, since they dissolve or become transparent in liquid scintillation fluid.
A swipe should cover a minimum surface area of 100 cm2, which is approximately equal to a 4" by 4" square. The wipe should be dry and taken using moderate finger pressure. Swipes of objects or lab locations must be kept separated to avoid cross contamination. Swipe packets make this easy, and are commonly available at the NIH Self Service Stores.
If counting results are reported in counts per minute (cpm), the results must be converted to decays per minute (dpm) using the counting efficiency, which is always less than one or 100%.
dpm = cpm / counting efficiency
The allowable limits for removable contamination for restricted or posted areas, where unsealed radionuclides work is performed and unrestricted or areas accessible to the public are given below.
The date and location of swipes only needs to be documented for the monthly survey report, NIH 88-12 Form .
If the swipe analysis indicates no removable contamination but a survey meter indicates a count rate of greater than twice background, contact the area health physicist for further instructions. Do not attempt to continue to decontaminate an object or lab location when contamination levels measured with a survey meter cannot be further reduced. The Area Health Physicist can consider regulatory limits for fixed contamination and advise the staff on what actions, if any, need to be taken to reduce radiation exposures for the fixed contamination.
Counting Methods for Swipes or Smears
Swipes or smears used to assess beta emitting radionuclide contamination must be analyzed with a liquid scintillation counter (LSC). Swipes or smears to assess gamma-emitting radionuclide contamination should be analyzed with a gamma counter.
While an LSC may be used to assess gamma contamination, close attention must be given to the efficiency of the counter for the radionuclide in question and the techniques used. The manufacturer or qualified service representative should calibrate counters on an annual basis. This calibration determines the counting efficiency for common radionuclides used at NIH, which must be used to convert between counts per minute (cpm) and disintegrations per minute (dpm) as indicated in the Surveying for Removable Contamination section above.
When possible, liquid scintillation samples should be dark adapted before analysis to reduce the effect of chemiluminescence, the emission of light due to a chemical reaction involving the scintillation fluid. This can be accomplished by simply leaving the rack in the counter with the cover closed for 30 minutes or more.
In addition, a blank or vial containing an unused swipe or smear should be counted for background measurements along with a calibration standard. For good counting statistics, vials should be counted for at least one minute each.