Surveying the Lab for Contamination


Surveying your lab is important to ensure contamination is not being spread. It also allows you to know where radioactive sources are and minimize any potential exposures. Are you trying to:

 

 

HOW TO DOCUMENT A SURVEY

Documented surveys shall reference a map of the area surveyed, or clearly describe the locations monitored. Records of the survey shall include

  • Locations where swipe samples were taken;
  • Printout results from swipes counting (Instrument printout shall be attached in its entirety, including counting date and instrument-specific information.);
  • Removable contamination reported in disintegrations per minute (dpm) (If counts per minute (cpm) are recorded, then the record shall also include a documented conversion to dpm.);
  • Locations where swipes indicated levels are above 200 dpm per 100 cm2, instrument contamination readings greater than 0.3 mR/hr, and area radiation levels are greater than or equal to 0.2 mR/hr;
  • Instrument used;
  • Date of survey;
  • Name or initials of person performing the survey.

When contamination or radiation levels are found above Table 2 or Table 3 action levels found in the Survey Requirements, then records shall also indicate the corrective action(s) taken to eliminate or minimize the excessive levels found, including the print out results of the re-surveyed areas. 

Inspection Survey Records shall be kept readily available for review by RW’s, AU’s, RSS, and NRC. 

 

HOW TO USE YOUR SURVEY METER

A survey meter is probably your most useful tool in assessing contamination in the laboratory when you are working with radioactive materials.  It can be used to identify areas of contamination in the work area and to survey areas where you don't suspect contamination.  It should also be used to check yourself to ensure that you have not contaminated your lab clothing, personal clothing and, most importantly, your skin.

Remember that when working with tritium (H-3) a standard G-M meter will not detect this isotope.  You must rely on swipe data for meaningful information.  Listed below are some helpful reminders on how to check your meter prior to surveys and how you should use them operationally.

 

PRE-OPERATIONAL CHECKS
  • Make sure your meter has been calibrated within the past year.
  • Use your battery check switch to ensure that there is enough battery power to operate your meter.
  • If a check source is attached to the meter, use it and compare the results to those indicated on the calibration sticker.  These numbers should agree within about 20%.  If no check source is available, check the meter against a known radiation source to ensure that it responds to a radiation field. 

Note: if your meter fails any of the above tests, it is not valid for meter surveys. You can request a loaner meter from EHS while yours is being calibrated or fixed. To have your meter calibrated, see the How to Maintain Instrument Calibrations section on this page.

 

OPERATION

When surveying for contamination using a pancake or thin-end G-M probe, use a slow sweeping (5-8 cm per second) motion about 1 cm away from the surface being tested.  Be careful not to touch the face of the probe with a sharp object or the tube will puncture (about $100 to replace). 

Remember to use the survey meter to check for areas where you also may want to swipe.  Just because you can't see contamination on the meter does not mean that it is not there.  Conversely, you may find contamination with the meter, but it may be "fixed" and not readily removable.

 

 

HOW TO USE YOUR LIQUID SCINTILLATION COUNTER

Before beginning actual system operation, the user should become familiar with the identification of all system controls and indicators and their functions as related to use during system operation by referring to the manufacturer's operation manual.

 

SAMPLE MEASUREMENT OPERATIONS

Ensure the power is applied to the system. 

Ensure the printer has an adequate supply of paper for the operation to be performed, and that the printer is in the ON-LINE mode. 

Load all standards and samples into the cassette. 

Select the appropriate protocol designator (usually a flag or id plate) for either general surveys with the typical 3 window set up or full open window for labs that only use a particular low energy isotope, i.e. Tritium.  If using a Packard, place the protocol designator on the first cassette of the batch.  Reset the cycle flag by pushing the slide toward the front end of the cassette. 

Load the cassette into the sample changer. 

Close the cover on the sample changer. 

Initiate counting by pressing the Count Start/Stop key, or Auto Start key. 

Get print-out results from the counting of your samples and attach to survey maps.  If counts per minute (cpm) are recorded, then the record shall also include a documented conversion to dpm.  In addition the LSC print should also have the date, protocols, background, and efficiency listed.

If swipes’ results are greater than 200 dpm, rerun those vials.  The vial(s) may have to be placed in a cold area prior to the rerun.. This cooling down should eliminate any chemical luminescence. If sample’s result is still higher than 200 dpm, initiate decontamination procedures. 

 

CAUTION

The swipe protocols are defined to meet your day-to-day use of the system.  They contain information like counting window settings of radionuclide’s you might select.  If you want to modify your swipe protocol contact your Assigned HP.  All the efficiency information is posted on your counter on the calibration sticker.  For those of you without automatic DPM, you need to use the posted efficiencies to convert counts per minute (CPM) to disintegrations per minute (DPM) by the formula of DPM = CPM/efficiency.

 

 

 

 

HOW TO PERFORM A SWIPE AND METER SURVEY

 

MATERIALS NEEDED
  • Drawing of the area to be surveyed,
  • Swipes,
  • Pen to mark the drawing and the swipes.  Swipes need to be marked or pre-numbered by manufacturer to match the swipe location on the drawings, 
  • Scintillation vials and media,
  • Liquid Scintillation Counter (LSC) and/or Gamma Counter, with a pre-programmed protocol or setting corresponding to the energy of the suspected contaminant (radioisotope), 
  • Survey meter to check contaminated swipes throughout survey for gross indication of contamination,
  • Pad or envelope to secure or hold the swipes as they accumulate, such that they do not "cross-   contaminate" other swipes, and
  • Gloves, safety glasses, and lab coat.

 

PERFORMING METER CONTAMINATION SURVEYS
  • Should be performed first to identify “hot” spots to be swiped.
  • Identify swipe locations on drawing of lab.
  • Number locations sequentially on drawing and on the corresponding swipe for that location.  Start in areas with the least potential for contamination and proceed to the areas with the greatest potential for contamination.  Identify the following:
    • "Hot" spot locations identified with survey meter, i.e., > 0.3 mR/hr;
    • "Use" areas, in addition to "hot" spots (floors, benches, equipment);
    • Storage areas, where material is used,
    • Waste,
    • Material transport areas (to and from storage/use/waste areas),
    • Areas you may have gone before surveying yourself (phone, desk, office, etc.),
    • Entrance to lab (floor), "no-use" areas,
    • Floor, desks, offices within lab, hallways, etc,
    • Telephone, handles (drawers, equipment, faucets, meter knobs, etc.), door knobs.

 

PERFORMING REMOVABLE CONTAMINATION (SWIPE) SURVEYS
  • "Swipe" areas with filter paper, making sure that the number on the swipe corresponds to the numbered location on the drawing, and that the area covered by the swipe is 100 cm2 .
  • Check suspected "hot" swipes with the survey meter so you can separate them from the rest of the swipes; a periodic check should be conducted of other swipes as well.
  • Swipes are now ready for sequential placement in scintillation vials and counting in the LSC or Gamma Counter.
  • The results should be analyzed and compared to the Removable Contamination Survey action limits of Table 2 (link policy here).


 

 

HOW TO MAINTAIN INSTRUMENT CALIBRATIONS

A list of your current active survey meters, Liquid Scintillation, and other counting equipment is available for you to see during routine quarterly inspections, and is printed on the quarterly reports.  You should report any discrepancies to your assigned HP.

If you have any questions regarding the operation of your instrumentation, you can contact your assigned HP or another member of EHS, and they will be glad to assist you. 

Your meters and instruments must be calibrated on an annual basis if they are actively used. In order to maintain your survey meter's calibration, you must fill out the Instrument Calibration and Repair Form found under Rad Forms to the right. Bring your survey meter to EHS at 180 General Services Building along with the filled out form. Make sure to include the MOCode you would like to use to pay for the calibration services. Do not fill out the bottom half of the form labeled as Internal Use Only. When your meter is ready to be picked up, you will receive an email notification. At that point, you should bring back the loaner meter if you were given one.

For benchtop instruments requiring calibration, EHS will contact you for a time to come out and calibrate the instrument. This too shall be done on an annual basis.

 

Page last updated on February 23. 2020.