Radiological Survey Measurement Approaches for Direct Readout of Effective Dose Rate, 20-R9724

Principal Investigator
Roland R. Benke

Inclusive Dates:  07/01/07 – 06/30/08

Background - External radiation dose is a primary consideration for operating and regulating many facilities that are licensed to possess radioactive material or radiation-generating machines. For example, radiation area designation (i.e., from radiation area to very high radiation area) is based on dose rate measurements. Effective dose is an improved, internationally adopted dosimetric quantity that represents a more realistic metric for human exposure to external radiation than alternative operational quantities. Recent changes in United States policy on radiological dosimetry have specified effective dose (equivalent) as the new primary quantity for external radiation protection. The effective dose concept, however, has been limited to calculations because methods for measuring this quantity have neither been developed nor demonstrated. Continued use of conventional survey approaches and simplified quantities can result in overly conservative radiation area designations and operational facility decisions. Radiation protection programs can benefit from advanced survey methods by

• Increasing realism and reducing conservatism in radiation area designations
• Optimizing temporary shielding and dosimeter placement
• Reducing unnecessary regulatory burden and operational costs by focusing resources on bona fide radiation hazards
• Improving as low as is reasonably achievable (ALARA) implementation for external radiation.

Approach - The objectives of this project were twofold:

• Develop and demonstrate survey measurement approaches to characterize features of gamma-ray radiation fields that are necessary for determining effective dose
• Develop numerical algorithms for converting survey measurement data into direct readout of effective dose rate.

Accomplishments - SwRI has overcome the described technical knowledge gap by developing a proprietary survey method to determine effective dose rate. This method alleviates reliance on simplified operational quantities. Laboratory measurements demonstrated the ability of the SwRI-developed advanced survey method to determine effective dose rate in a complex radiation field. To test the robustness of the method, laboratory measurements were performed in low, near-background radiation fields. Because intrabody shielding and dose equivalent radiosensitivity differ for individual organs, the dose rate at a specific location depends on the receptor-facing direction in the radiation field. The advanced survey method results preserve this directional dependence, as shown by the video presentation in Figure 1 for a hypothetical operational facility. This advanced survey method is:

• Inexpensive – Successful with common radiation instrument
• Fast – Short instrument measurement times
• Practical – Heavy hardware not required
• Better – Characterize radiation field; identify localized radiation; determine effective dose rate.

Figure 1. Nonproprietary video presentation of the advanced survey method shows dependence of resulting dose rates on the receptor-facing direction in the radiation field. Colored halos highlight radiation sources within a hypothetical operational facility. (Choose video format: Windows Media | Quicktime )

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