Answer to Question #352 Submitted to "Ask the Experts"

Category: Doses and Dose Calculations — External dose calculations

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

Can you identify any regulatory approval or precedent set for modification of the whole body weighting factor of 1.0 for exposure of individuals wearing one dosimeter or two dosimeters (one at the collar and one at the waist under a lead apron)? If approved, this could allow a worker to receive more than 5000 mrem per year CEDE. If approved, what would be the conditions under which a dosimetry algorithm would be applied? (a) All workers? (b) Selected workers approaching a limit?

We suggest you consult American National Standard HPS N13.41-1997, Criteria for Performing Multiple Dosimetry. Pages 15-16 give examples of the use of two or more dosimeters and assigning an effective dose equivalent through the weighted combination of the several monitored compartments. One of the examples involves the diagnostic radiology situation with two dosimeters, one on the trunk under the apron and the second at the collar over the apron.

With regard to your statement that the procedure could allow a worker to receive more than 5000 mrem per year CEDE, this should not happen for the case of two or more badges. The effective dose equivalent is the summation over tissues of the product of the dose equivalent to a tissue and the respective tissue weighting factor. The method presented uses the available dosimeter information to derive a best estimate of the total body effective dose equivalent--it assigns doses to compartments on the basis of the respective dosimeter readings, uses compartment factors related to the ICRP tissue weighting factors to compute compartment contributions, and then sums over compartments to estimate the effective dose equivalent.

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Charles E. Roessler, Ph.D., CHP

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