Fast measurement of the quasi-monochromatic MeV γ-beam flux using the 63Cu( γ, n)62Cu reaction at the Shanghai Laser Electron Gamma Source

Abstract

Shanghai Laser Electron Gamma Source (SLEGS) is a powerful laser-Compton scattering (LCS) $\gamma$-ray facility that provides a quasi-monochromatic MeV $\gamma$-ray beam with a moderate flux of 10${}^5$-10${}^7$ photons/s. Accurate and fast measurement of the SLEGS $\gamma$-beam flux is critical for the upcoming photonuclear experiments. In this study, an activation method based on ⁶³Cu($\gamma$, n)⁶²Cu reaction is proposed for fast measurement of the SLEGS $\gamma$-beam flux. By operating at a low beam flux of 10${}^4$-10${}^5$ photons/s, the SLEGS $\gamma$-beam flux is measured within the energy range of 11.66-19.08 MeV. The $\gamma$-beam flux as a function of laser power is also investigated. It was found that the flux data obtained by the proposed method is in reasonable agreement with the online monitoring of the LaBr${}_3$ detector and the GEANT4 simulations. The dependence of the total time (the sum of the irradiation time, the cooling time, and the detection time for identifying characteristic $\gamma$-ray emission) on the $\gamma$-beam flux is further studied. The total time could be controlled within 100 s when the beam flux exceeds 10${}^8$ photons/s, suggesting the great potential of the ⁶³Cu activation method to quasi-real-time measure the LCS $\gamma$-ray beam at high flux conditions.