beta- and gamma-Comparative dose estimates on Enewetak Atoll

Area of Science:

• Environmental Science
• Radiation Physics
• Nuclear Chemistry

Background:

• Enewetak Atoll was a site for atmospheric nuclear weapons testing.
• Marshallese populations are returning to affected Pacific atolls.
• Understanding radiation exposure is critical for resettlement.

Purpose of the Study:

• To quantify beta and low energy gamma contributions to external radiation doses.
• To assess radiation exposure for returning Marshallese populations.
• To compare current dose estimates with previous surveys.

Main Methods:

• Field measurements using thermoluminescent dosimeters (TLD), pressurized ionization chambers, NaI detectors, and GM probes.
• TLD measurements with and without beta-attenuators to differentiate dose components.
• Calculation of integral 30-year external shallow dose estimates.

Main Results:

• Beta and low energy gamma radiation account for approximately 29% of the total dose rate at 1 meter in air.
• Ground cover significantly influences beta dose; vegetation reduces it, but dense vegetation has diminishing returns.
• Integral 30-year shallow dose estimates are 25-50% higher than whole-body estimates.

Conclusions:

• Beta and low energy gamma radiation are significant contributors to external radiation doses at Enewetak Atoll.
• Remedial actions can effectively reduce shallow dose contributions due to the low penetration of these radiation types.
• Accurate dose assessment is vital for the safe return of the Marshallese population to their homeland.