Establishment of a low dose rate Ba -ray calibration field for photon energy in the 300-400 keV range

Tsuji, Tomoya   ; Yoshitomi, Hiroshi   ; Kowatari, Munehiko*; Sato, Fuminobu*; Tanimura, Yoshihiko   

A -ray calibration field using a sealed Ba source for photon energy in the 300 - 400 keV range was established at the Japan Atomic Energy Agency to evaluate radiation protection devices under low dose rate conditions. To suppress low-energy -ray components, a 2-mm lead filter was applied. The photon fluence spectrum was measured using a CdTe spectrometer and an unfolding method, yielding a spectrum with a mean energy of 321 keV. Reference air kerma rates were determined using ionization chambers calibrated in a Cs field, with energy correction factors applied. Spectrometry using a CeBr scintillation spectrometer combined with the G(E) function method was employed to validate these corrections. Spectrum-averaged conversion coefficients were derived from the measured spectrum, indicating equivalence to the N-400 radiation quality. This field provided air kerma rates from 0.22 to 2.13 Gy h, suitable for testing devices used in environmental monitoring and nuclear emergency response.