Unfolding environmental γ flux spectrum with portable CZT detector

Environmental γ-rays constitute a crucial source of background in various nuclear, particle and quantum physics experiments. To evaluate the flux rate and the spectrum of γ background, we have developed a novel and straightforward approach to reconstruct the environmental γ flux spectrum by applying a portable CZT γ detector and iterative Bayesian unfolding, which possesses excellent transferability for broader applications. In this paper, the calibration and GEANT4 Monte-Carlo modeling of the CZT detector, the unfolding procedure as well as the uncertainty estimation are demonstrated in detail. The reconstructed spectrum reveals an environmental γ flux intensity of 3.3±0.9×107 (m2⋅sr⋅hour)−1 ranging from 73 to 3033 keV, along with characteristic peaks primarily arising from 232Th series, 238U series and 40K. We also give an instance of background rate evaluation with the unfolded spectrum for validation of the approach.