Neutron Detectors for FDS and FDSi

Beta-delayed neutron emission (βn) is a prevalent decay mode for the majority of neutron-rich nuclei yet to be discovered in the current and future radioactive ion-beam facilities. In decay experiments, neutrons will become a probe of increasing importance as they often become the primary source of nuclear structure information for the investigated nuclei. In the FDS concept, neutron counting and neutron energy measurements are integral components of the design. Within 3 years of the FDSi's operation, the viability of neutron spectroscopy using time-of-flight arrays and total-absorption spectroscopy was successfully demonstrated in multiple measurements [1,2,3]. In the near-term, the FDSi will utilize its existing and proven arrays. To capitalize on the FRIB discovery potential for neutron drip-line and r-process nuclei, the capabilities of the FDS will require a new generation of neutron detectors. Design will leverage the capabilities of new, promising materials and analysis methods using machine learning. The current focus of the FDS neutron detector design efforts is on a highly segmented detector, which leverages the neutron tracking capabilities demonstrated by the NEXT array [4,5,6]. It requires neutron-gamma discrimination, maximizes neutron detection efficiency, and neutron energy resolution in the 0-5 MeV range. It has to be capable of measuring multiple neutrons emitted simultaneously and accommodate an efficient gamma-ray detection system. The ongoing R&D efforts to realize a new neutron detector for FDS need to reconcile these often conflicting requirements and will capitalize on recent measurements with NEXT array [7].

[1] I. Cox et al., Phys. Rev. Lett. 132, 152503 (2024).

[2] J. Peltier et al., Phys. Lett. B 866 139576(2025).

[3] N. Braukman et al. APS DNP (2025).

[4] J. Heideman et al. NIM A 946, 162528,(2019).

[5] S. Neupane et al., NIM A 1020, 165881, (2021).

[6] S. Neupane et al., Phys. Rev. C 110, 034323 (2024).

[7] P. Dyszel et al., submitted to Phys. Rev. Lett. (2025).