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× 10^7  (m^2·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.