Operational Quantities for External Radiation Exposure

Draft document: Operational Quantities for External Radiation Exposure
Submitted by Norio Tsujimura, Japan Atomic Energy Agency
Commenting as an individual

I’d like to appreciate the report committee’s efforts to construct a unified system of operational dose quantity extended to the GeV energy region. However, I am concerned that the newly proposed system is hard to be implemented in operational monitoring as well as it is not amenable to measurement by personal dosemeters.

The dose quantities that can be measured by a personal dosimeter placed on the surface of a human body is those defined near the wearing position, which totally differ from the dose averaged over the bulk body (i.e., the effective dose) in terms of the angular dependence. The compromised solution to this fundamental problem should have been a judicious use of the "fail-safe" nature of the operational dose quantity Hp(d), which provides a conservative estimate to the effective dose in most exposure geometries. Bartlett and Dietze refer to the Hp(d)’s conservative nature as “penalizing”, but I have interpreted this as benefit. The use of Hp(d) provided us simplification in the interpretation of dosemeter readings and the calibration procedure in routine monitoring, freeing us from cumbersome tasks such as the calibration tailored for job-specific exposure geometries. However, with the new operational dose quantity Hp, the “fail-safe” function is not guaranteed. As suggested in the second paragraph of chapter 6.1, therefore, users or dosimetrists will be required to make non-AP calibration or select a suitable angle of incidence for calibration, based on the conditions which are considered most likely to be encountered at workplaces, e.g., ROT, ISO, or a combination of these and AP. I believe the choice of the optimal calibration conditions will be tough tasks.

In addition, the current Hp(d) has the versatility applicable to any partial body exposures. The new E-like dose quantity Hp appears obviously inappropriate for personal dosemeters attached to the upper arms or thighs in multi-badging procedures in non-uniform exposure conditions.

I understand the needs to extend the operational dose quantity system to higher energy regions. However, the impact of the change in the operational dosimetry system should be measured by how much workers are actually affected. It is unlikely that those who receive high-energy radiation exposure occupy much of the work forth. A possible solution might be to recommend the use the effective dose instead of Hp(10) for such workers.

I recognize that I’m somewhat conservative on this matter, and my opinion is limited to ordinary energy-range work environments.

I hope my comment be stimulating discussion.

D. T. Bartlett and G. Dietze, Radiat Prot Dosim 139(4), 475-476, 2010.
J. R. Harvey and G. Portal, Radiat Prot Dosim 54(3/4), 183-187, 1994.