Unfolding of sparse high-energy $\gamma$-ray spectra from LaBr$_{3}$:Ce detectors

TL;DR

This study evaluates unfolding methods for high-energy gamma-ray spectra from LaBr3:Ce detectors, finding the iterative approach superior in qualitative accuracy and speed, suitable for real-time analysis at ELI-NP.

Contribution

It compares unfolding techniques for high-energy gamma-ray spectra, demonstrating the iterative method's advantages in accuracy and computational efficiency.

Findings

Iterative unfolding provides the best qualitative spectrum reproduction.

Correlation fluctuations are significantly reduced with the iterative method.

Iterative approach is faster and suitable for semi-online data analysis.

Abstract

Here we report on the characterization of one of the large-volume LaBr$_{3}$:Ce detectors for the ELIGANT project at ELI-NP. The main focus of this work is the response function for high-energy $\gamma$ rays of such detectors. In particular, we compare a selection of unfolding methods to resolve small structures in $\gamma$-ray spectra with high-energies. Three methods have been compared using $\gamma$-ray spectra with energies up to 12 MeV obtained in an experiment at the 3 MV Tandetron\texttrademark\ facility at IFIN-HH. The results show that the iterative unfolding approach gives the best qualitative reproduction of the emitted $\gamma$-ray spectrum. Furthermore, the correlation fluctuations in high-energy regime from the iterative method are two orders of magnitude smaller than when using the matrix inversion approach with second derivative regularization. In addition, the iterative method is computationally faster as it does not contain large matrix inversions. The matrix inversion method does, however, give more consistent results over the full energy range and in the low-statistics limit. Our conclusion is that the performance of the iterative approach makes it well suitable for semi-online analysis of experimental data. These results will be important, both for experiments with the ELIGANT setup, and for on-line diagnostics of the energy spread of the $\gamma$-ray beam which is under implementation at ELI-NP.