Answer to Question #8522 Submitted to "Ask the Experts"

Category: Radiation Workers

The following question was answered by an expert in the appropriate field:


I am a biologist and have been working with 35S a lot recently. I have been running acrylamide gels containing about 14.8 kBq of radiation per lane (total about 148 kBq per gel). This radiation is not measureable by a Geiger Muller (GM) counter and I have therefore been concerned about the risk of unnoticed contamination and incorporation after accidental contact. I know liquid scintilation is an appropriate monitoring method, but this cannot be performed continuously during an experiment (unlike a GM counter constantly turned on). Are my worries justified, or are these not detectable quantities and potential contaminations (activity way under ALI) "negligible?"


Thank you for your question. 148 kBq is a very small activity and, if accidentally ingested, would not cause a harmful effect.

However, 35S is easily detectable with a GM with a "pancake" probe on it. This probe is about 5 percent efficient for the 35S beta so 148 kBq would be roughly 440,000 cpm. Regardless of whether the activity is harmful if ingested, to prevent unnecessary contamination and ingestion, this type of meter should be used for routine surveillance of the work area and of hands.

A liquid scintillation counter is still the gold standard, but you're quite right, it isn't terribly helpful for routine monitoring!

Kelly Classic
Certified Medical Health Physicist

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