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Answer to Question #6058 Submitted to "Ask the Experts"Category: Environmental and Background Radiation — Building and Construction Material The following question was answered by an expert in the appropriate field: Q
I was surveying radioactive tiles in the kitchen and bathroom which I
assumed were uraninum glaze. I measured 1,200 and 2,400 cpm
respectively, with a pancake probe on contact with the tiles. Is there
a rule of thumb to convert the cpm to mrad/hr to obtain a possible skin
dose from the beta particles? The gamma component was minimal. I
measured 0.05 mrem/hr with a pancake detector in contact with the
tiles. The background level was 0.01 to 0.02 mrem/hr.
A
The response of each instrument/detector combination is different so
there is no single answer to give. But a pure uranium slab delivers
about 220 mrem at the surface. Your tiles, being only partially uranium
and not of so-called infinite thickness, would deliver a much lower
dose rate at the surface. Measurement with a pancake detector in
contact with the tiles does not give a surface dose since the effective
center of the detector is some distance from the tiles. Accurate
surface dose-rate measurements require special instrumentation such as
extrapolation chambers. A more meaningful measurement would be at
locations where persons are. But a Geiger counter may or may not be an
accurate way to measure these levels as Geiger-type instruments are
notoriously energy dependent and need to be specifically calibrated for
the energy and type of radiation being measured.
Answer posted on 9 March 2007. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.
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