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News and training for radiation workers at Northwestern University Number 76 June 2006

Inspection Findings: Inadequate Surveys

During April 2006, representatives of the Illinois Emergency Management Agency conducted an inspection of the activities authorized under the University’s Broad License authorizing the use of radioactive material for research and instruction. As part of the inspection, several laboratories in which radioactive materials are used were picked at random for the inspectors to visit. The inspectors checked for accountability records and proper warning signs and performed a survey for radiological contamination.

In one laboratory on the Evanston campus, the survey revealed a spot of significant contamination on a workbench where no work had occurred for more than a week. Because of this finding, a Notice of Violation was sent stating that the University failed to ensure that adequate surveys were performed to identify potential radiation hazards that might be present. They felt that, because the work had been completed much earlier, the user surveys should have detected the contamination, thus indicating a need for replacing the bench paper. During the last inspection in January 2005, the University was similarly cited for failure to perform an adequate survey in a lab on the Chicago campus.

Both violations could have been avoided if the workers in the radiation lab had been more aware of proper survey techniques. Many people perform surveys with their pancake G.M. probe too quickly. The screen side of the probe should not be more than one centimeter from the surface being surveyed and must travel slowly (about one inch per second) in order to maximize its sensitivity. If the probe moves too fast, it won’t capture enough events on which to base a conclusion. Correctly performed, a survey with the pancake G.M. is an excellent method for detecting contamination from S-35, C-14 and P-32.

If your lab uses tritium or I-125, the pancake is not your instrument of choice for the most sensitive surveys. For I-125 a thin crystal sodium iodide probe should be used, employing the same technique regarding closeness to the surface and probe speed. For tritium, there is no portable survey meter that can detect a beta particle of such low energy. The only method for finding tritium contamination is taking wipes and counting them in the Liquid Scintillation Analyzer.

Every lab worker at Northwestern who uses radiotracers is required to perform a survey of the work area after each use of radioactive materials. Those work area surveys and frequent general area surveys throughout the lab help ensure that inadvertent contamination is identified and removed before it can spread to areas outside the laboratory. Although records of these surveys are not required, the records can be helpful in demonstrating safe work practices in the lab. If these surveys are performed using the guidelines described above, no additional survey violations should ever occur.

Use this NUtrino as a training tool for new workers and required annual refresher training for current workers. Circulate it among the radiation workers in your group and have them sign and date the training form on the back. File it with your authorization and other radiation safety documents for review during regulatory inspections. Discuss it during laboratory meetings. We have back issues, or you can print them off the web at http://www.northwestern.edu/research-safety/rad/nutrino/index.htm.

Office for Research Safety - Office for Research - Radiation Safety Committee

Ward B-106 Chicago Campus, phone 3-8300 Tech NG71 Evanston Campus, phone 1-5581