Accelerator-driven photon reference field for replacement of 137 Cs γ-ray

A transition to a mechanical source for x-ray reference field is desired to replace high-activity Co-60 and Cs-137 gamma-ray sources for enhancing nuclear security and safety management. The National Metrology Institute of Japan (NMIJ) developed a new photon reference field using an electron beam from a linac with energy less than 1 MeV. The effective energy of the photon field is comparable with Cs-137 gamma-ray. The air kerma rate in the reference field was validated by comparing a commercial cavity ionization chamber to the NMIJ standard reference field. The calibration constants were consistent within 0.8% for every relative extended uncertainty ( k = 2).