Answer to Question #10572 Submitted to "Ask the Experts"

Category: Radiation Workers

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

Q
Why do we wear a TLD (thermoluminescent dosimeter) badge outside our lead apron and not under it?
A
There are two main reasons we wear the TLD badge outside the lead apron. The first is to measure, or be able to estimate from the badge reading, radiation dose to the organs not covered by the apron—eyes, thyroid, etc. The other reason is that, depending on the level of exposure, the apron does such a good job of shielding that there is no measurable exposure underneath it. So if we relied only on that badge, we'd have no information.

While most manufacturers state, for a 0.5 mm lead-equivalent apron, that about 5 percent of the radiation gets through the apron, we have found that the number is much smaller. That statement might be true for the primary beam, but since most workers are exposed only to scattered radiation, the aprons are nearly 100 percent effective at stopping the scattered x rays. That is why it is difficult to detect anything under the apron.

Kelly Classic
Certified Medical Health Physicist
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