How to Perform a Swipe Survey
Determining the existence of loose radiation contamination in the lab is paramount to the safety of lab personnel. A swipe surveys, also referred to as a wipes or a radiation swipe tests, are the essential tool used to do so. Most swipes, depending on the application, are counted with the appropriate radiation detector. These detectors can range from liquid scintillation counters (LSC) to the tried and true “pancake” detector, such as the one in the Radiation® Alert Ranger, which has a Wipe Test Plate option for ease of use and portability when conducting these checks in the field or on the go. Swipe tests have been considered the most reliable method of determining contamination without the use special equipment.
Be sure to start with the appropriate media (paper filters, cotton swabs, glass fiber filters, etc.) and take note of the sampling areas you are testing for contamination. Swipes for use with the Ranger are available from S.E. International, Inc. in various quantities. Typically, swipes should cover an area of about 100 cm2. Aside from identifying the area of potential contamination, determining your sample area will also help prevent the spread of any loose particles, and with it, the area of contamination. Note that went performing a swipe of the area, that users should take precautions to avoid potentially contaminating themselves while collecting samples by using the appropriate protective gear, such as disposable gloves, face masks, etc., for the scenario at hand.
To take a swipe, the same amount of pressure you would use if cleaning up a spill with a wash cloth or a sponge and pretend as if you are drawing an “S” over a portion of your sample area. Be sure to separate and log the swipes to prevent cross contamination between the samples.
Once you have collected your swipe samples, you will need to establish your background levels so that you can determine your baseline, or “zero”. This can be achieved by placing a clean swipe in the sample counter, such as the Ranger wipe test plate, and taking a timed count. Be sure to use whichever counting protocol included in the procedures for your laboratory to determine count times, the frequency of testing required, acceptable thresholds, and the units of measurement required for reporting purposes. Some facilities recommend using a control sample, which is a known check source with a specific activity to test If you know beforehand the radionuclides being used by your lab, you can program the specific isotope efficiency into the Ranger establish the activity, in addition to the overall sample rate if your reports require readings in Becquerels (Bq) and Disintegrations Per Minute (DPM).
Once your background has been recorded, you can easily identify potential contamination, as any swipe test found to have a count rate greater than two times (2X) the count rate of the background sample would be a potential source. Finally, record the contamination survey results on the Radioactive Contamination Survey Record (RSS). Some results of wipe tests must be kept in a Radiation Safety Manual for a minimum of five (5) years. In those instances, records should include a laboratory map, the results from the sample, and Wipe Test Calibration Work Sheets for establishing more accurate contamination levels.
In the event that you have contamination, you should consult with your Radiation Safety Officer on procedures for decontamination before returning to conduct another test to ensure the clean-up was performed adequately.