A Compton-based filter stack spectrometer for high-fidelity MeV x-ray spectrum unfolding.

High-energy x-ray sources are widely used across many fields and industries. Understanding and characterizing these sources is critical for these potential applications and uses. The filter stack spectrometer (FSS) is a compact and portable diagnostic that employs a stack of alternating image plate detectors and filters, and when paired with the unfolding routine based on randomized perturbative minimization methods, it can characterize these sources with high accuracy. However, limitations such as large measurement uncertainties and flattened attenuation curves in the MeV photon range make the spectral inversion difficult and less accurate. In this paper, we present a novel filter stack design that enhances the sensitivity of the FSS by leveraging Compton electrons generated in high-Z filters. This approach produces a more distinct diagnostic signal, making the spectrometer better suited for higher photon energies and more resilient to experimental uncertainties. We also demonstrate the design process for the filter stack through our modular Monte Carlo N-particle approach, allowing us to calculate response matrices rapidly.