Beta decay studies with ORNL Modular Total Absorption Spectrometer

The Modular Total Absorption Spectrometer (MTAS) has been used for the studies of complex beta decay patterns of fission products since 2012 at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL). Within 2018 to 2021 period, MTAS was measuring beta-decays of 252Cf fission fragments at the CARIBU facility at Argonne National Laboratory. In 2022, MTAS was commissioned with the 82Se fragmentation beams at the Facility for Rare Isotopes Beams (FRIB). MTAS is a one ton array of 19 NaI(Tl) segments and auxiliary beta detectors including segmented silicon counters [1,2], and most recently the pixelized scintillator ion implantation-beta decay array for the fragmentation studies [3], now shielded with about 6 tons of lead. MTAS studies focused on the decay heat released from fission products abundant during the nuclear fuel cycle, via the reliable determination of the complete beta-decay patterns from measured gamma radiation. The corresponding anti-neutrino energy spectra were deduced and use to analyze the reactor anti-neutrino anomaly and related concepts of sterile neutrino. Selected earlier results [4,5] and the most recent ones [6,7,8,9] including an attempt to measure 55Ca decay with MTAS at FRIB, will be presented.

[1] B.C. Rasco et al., NIM A788, 137, 2015.

[2] M. Karny et al., NIM A 836, 83, 2016.

[3] R. Yokoyama et al. NIM A, 937, 93, 2019.

[4] B.C. Rasco et al., Phys. Rev. Lett. 117, 092501, 2016

[5] A. Fijałkowska et al., Phys. Rev. Lett. 119, 052503, 2017.

[6] P. Shuai et al., Phys. Rev. C 105, 054312, 2022.

[7] B. C. Rasco et al., Phys. Rev. C 105, 064301, 2022.

[8] M. Wolinska-Cichocka et al., Phys. Rev. C 107, 034303, 2023

[9] A. Laminack et al., to be submitted to Phys. Rev. C