Laboratory Surveys

The KUMC Radioactive Materials License requires that periodic laboratory surveys for radioactive contamination be conducted.  The survey results will assist in identifying possible problems in radioisotope handling procedures.  New radioactive materials users or individuals unfamiliar with performing routine surveys can contact the Environment Health & Safety office for in-person guidance on survey technique and how to interpret results.

Contamination surveys should include swipes analyzed using a liquid scintillation counter (LSC) or gamma counter, or direct surveys using hand-held instruments, or both.

For swipe surveys a piece of filter paper is rubbed over the surface being checked.  If any removable radioactive contamination is present, some of it will transfer to the swipe paper.  in order to be effective, a large area of the surface being checked should come into contact with the swipe.  It is best if the swipe is pressed down with gloved fingers (rather than forceps, for example) when taking the swipe.  Swipe surveys will work with any radioisotope.  Their only limitation is if the radioactive material has become FIXED to the surface -- as is the case sometimes with contamination of porous materials like concrete.

Swipe Technique

For direct surveys using hand-held survey meters (like geiger counters), proper survey technique is also important.  The surveyor should hold the probe close to the surface being checked without touching it (so that the contamination is not transfered to the meter itself).  They must also survey very slowly, moving the meter at a rate of about one inch per second.  Direct surveys are most effective with high-energy beta emitters like P-32, Rb-86 and Fe-59.  They are less effective for lower energy beta emitters like P-33, S-35 and C-14 due to their much lower efficiency of detecting these radioisotopes (see also the table below).  Direct surveys cannot detect H-3 at all since the low energy beta particle for that radioisotope cannot penetrate the covering of the detector.

Approximate efficiencies for Geiger Counters at 1 inch from a point source:

Radioisotope

Efficiency of Detection

H-3

Not detectable

C-14, S-35

0.2% - 0.8%*

P-32, Rb-86

3% - 8%

I-125

0.01% - 0.03%

* Not detectable if the detector window is covered with paraffin film, plastic wrap, or other material. [Ref. Worcester Polytechnic Institute Radiation Safety Training, 2009]

A thorough laboratory survey will include swipes or a direct survey on all areas with a high risk of being contaminated as well as areas where there is less risk but high traffic (for example, refrigerator or cabinet handles, the floor at the entrance to the lab, and sinks and benchtops where radioactive materials are NOT typically used).

If possible, swipes should be taken over at least approximately ten square centimeters of area using moderate pressure.  This is important in order to adequately interpret the results.  For example if one person uses a swipe to wipe every square inch of a benchtop, while another typically wipes only two square centimeters of area, and they both discovered 100 cpm above background, the resulting contamination levels would be interpreted quite differently.  On the other hand, it is appropriate to swipe less than 10 cm2 if the area or item has less than 10 cm2 of surface area.

If a liquid scintillation counter is used to assay the radioactive samples in your research, then this is a reasonable instrument to use to assay the swipes.  Place each swipe (e.g., filter paper) in its own counting vial, add scintillation fluid, shake and count the vial.  To appropriately measure the background, analyze a clean, unused swipe exactly the same way you will be analyzing the used swipes.

If a gamma counter is used to assay the radioactivity of your research samples, then use the same counter to count the swipes and use a survey meter such as a Geiger-Muller counter to survey for radiation levels on work surfaces.  It is recommended that a survey meter with an audible signal be used for this type of survey.  The audible signal has a faster response and it allows the surveyor to watch the area being surveyed instead of the survey meter.  The probe should be moved slowly above the work area (1/2 inch above), and the meter response monitored for a signal increase.  This type of survey is recommended for high-energy beta and gamma sources.

If the contamination survey of any areas shows activity greater than background levels, it is good lab practice to decontaminate and re-survey these areas until all swipes are approximately background.  On the other hand, if any areas show activity greater than 220 dpm/100 cm2, these areas must be decontaminated and re-surveyed until all swipes are less than 220 dpm/100 cm2.  More information about performing a contamination survey can also be found on page 2 of the Area Radiation and Contamination Survey form.

Periodic surveys may be conducted on a random, unannounced basis by the Environment, Health & Safety Office to monitor radioactive material handling practices.

Daily Surveys

Researchers are required to perform a survey at least daily when radioactive materials are in use.  This survey is documented by initialing the "Radioactive Materials Package Receipt and Disposal Record" (the last column of the table) that is provided by EHS for each package of radioactive material.  An example of this record is below.  Researchers would note the survey instrument's information in the yellow areas and initial in the red box for each day the material is used.  Researchers will turn this form in to EHS when the last of the radioactive material described on the form has been used and is picked up by EHS as radioactive waste.

Rad Mtl Recpt and Disposal Form

Monthly Surveys

Also, for most work with radioactive materials, researchers are required to perform a more thoroughly documented survey on a monthly basis - to be turned in to the EHS Office.  This survey will be documented on the Area Radiation and Contamination Survey Form and will include a drawing of the lab indicating where swipes were taken, which survey meters are available in the lab, what radioisotopes were present, and other information pertinent to radiation safety. 

A routine survey is not required when all radioactive materials and radioactive waste have been removed from the laboratory. However, a survey is still required if  the Authorized User has radioactive waste or other radioactive materials present in the laboratory - even if these radioactive materials have decayed to essentially zero activity.  This helps to ensure timely removal of waste materials and shipping containers.   Reports indicating the results of the surveys must be sent to the Environment, Health and Safety Office.  The laboratory and the Environment, Health & Safety Office should maintain copies of the survey.

Survey Technique

Last modified: Jul 01, 2014
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