Speakers
Description
Current metrological frameworks exhibit a significant traceability gap between ambient background levels and standard calibration intensities, complicating the characterization of radiation detectors at low dose rates. This study addressed this limitation by developing an environmental-level air kerma rate calibration system using a Co-60 source with lead attenuators (3.5–9.0 cm) in compliance with ISO 4037, effectively bridging the dose rate interval from 0.2 πSv/h to 10 πSv/h. Physical purity of the radiation field was maintained through the integration of a lead shield designed to isolate the measurement point from background radiation. Combined with a 10 L large-volume graphite-walled spherical ionization chamber and nitrogen-purging technology, the system effectively eliminated natural radon progeny interference and suppressed leakage current, achieving a high signal-to-noise ratio. The geometry of the radiation field was defined by X and Y axes, with spatial uniformity rigorously quantified through scanning measurements using an AT1121 detector; the results demonstrated a deviation of less than 5%, fully satisfying the stringent requirements of the ISO 4037 standard.
Regarding spectral characterization, Monte Carlo simulations were employed to model spectral degradation and derive energy correction factors, which were subsequently cross-validated with empirical spectra from a high-purity germanium detector. This protocol ensures field accuracy by effectively compensating for spectrum-shift induced errors. Following ISO GUM guidelines, uncertainty components including electrometer repeatability, geometric positioning, and environmental corrections were analyzed. Experimental results demonstrate that the system maintains high metrological stability across its entire range, with the combined standard uncertainty (uc) characterized at 0.52% for the unattenuated reference field and remaining precisely controlled at 0.60% even under extreme 9.0 cm Pb attenuation. This system establishes a robust metrological benchmark, ensuring international traceability and standardized measurement for low-intensity environmental radiation monitoring.
Keywords: traceability gap ; 10 L large-volume graphite-walled spherical ionization chamber; spatial uniformity; spectral characterization