Unfolding environmental ${\hat{I}}^3$ flux spectrum with portable CZT detector

Abstract

Environmental ${\hat{I}}^3$-rays constitute a crucial source of background in various nuclear, particle and quantum physics experiments. To evaluate the flux rate and the spectrum of ${\hat{I}}^3$ background, we have developed a novel and straightforward approach to reconstruct the environmental ${\hat{I}}^3$ flux spectrum by applying a portable CZT ${\hat{I}}^3$ 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 ${\hat{I}}^3$ flux intensity of $3.3\pm 0.9\times 10^7$~ (m${}^2\cdot$sr$\cdot$hour)${}^{-1}$ ranging from 73 to 3033~keV, along with characteristic peaks primarily arising from ${}^{232}$Th series, ${}^{238}$U series and ${}^{40}$K. We also give an instance of background rate evaluation with the unfolded spectrum for validation of the approach.