A novel method for measuring the energy spectrum of an inverse Compton scattering source based on nuclear resonance...

Inverse Compton scattering (ICS) gamma ray sources are capable of producing quasi-monochromatic, continuously tunable, high-brightness, precisely polarization-controllable, and ultrashort gamma ray pulses in the energy range from tens of keV to several MeV or even higher. The energy spectrum measurement of an ICS source not only serves as a key indicator of the device operating status but also provides foundational information. In this paper, we proposed a novel method of using nuclear resonance fluorescence (NRF) as a probe for spectrum measurements. By utilizing the continuous tunability of an ICS source, NRF photons can be excited at different points across the spectrum. The shape of the energy spectrum can then be effectively scanned and reconstructed by recording the relative NRF yields at different energy points. The feasibility of the proposed method was validated by Geant4 simulations of measuring NRF photon emission from 56Fe irradiated by an ICS source. We utilized the 845 and 3449 keV NRF photons of 56Fe to measure a Gaussian spectrum and a segmented Gaussian spectrum, which correspond to ICS spectra under different collection angles. The simulation results showed high precision for quasi-monochromatic gamma ray spectrum measurements, with a normalized root mean square error of less than 5%. To maintain a sufficient signal-to-noise ratio during the measurement, the energy resolution of detectors is suggested to be less than 1% of the energy being measured. Given an energy tuning precision of ΔE, the minimum measurable width of the energy spectrum, in terms of standard deviation, can reach 0.85 ΔE. Further experiments are needed to validate its practical feasibility.