Answer to Question #12291 Submitted to "Ask the Experts"

Category: Radiation Basics

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

Q

For an inhalation of tritium water vapor, which of the following is the correct equation for computing total effective dose equivalent (TEDE) based on committed effective dose equivalent (CEDE)?

TEDE = CEDE + (0.5)(CEDE)

or

TEDE = (1.5)(CEDE)

A

The TEDE includes dose from external radiation sources as well as dose from internally deposited radionuclides. In the case of tritium exposure, external dose is of no significance since the low-energy beta radiation from tritium decay is not able to penetrate the dead skin layer.

As written, both of your equations are numerically the same, and neither is correct. The CEDE includes intakes from all pathways, including penetration through the skin as well as inhalation—the two pathways that account for tritium intake by an individual submerged in an atmosphere containing tritiated water. An individual exposed to an atmosphere containing tritiated water vapor is assumed to take into his/her body twice as much through inhalation as through skin penetration. I think you perhaps intended that the CEDE refer to only the committed effective dose from inhalation; in that case, either one of your proposed answers would have been correct:

TEDE = (1.5)(CEDEinhalation)

where CEDEinhalation refers to the committed effective dose from the inhaled tritium alone.

George Chabot, PhD

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