Complete?-decay patterns of 142Cs,142Ba, and 142La determined using total absorption spectroscopy

Background: The decays of fission products produced in nuclear fuel are important for nuclear energy applications and fundamental science of reactor antineutrinos. In particular, nuclear reactor safety is related to the decay modes of radioactive neutron-rich nuclei, primarily via the emission of gamma rays, neutrons, and electrons. Additionally nuclear reactors are the most powerful man-made source of antineutrinos emitted during the decay of fission products. These antineutrinos are used to inspect fundamental properties of leptons as well as informing reactor operation. However, the majority of data on complex decays of fission products collected in the evaluated nuclear data repositories like Evaluated Nuclear Structure Data File (ENSDF) and Evaluated Nuclear Data Files (ENDF) are based on low-efficiency and often incomplete measurements resulting in questionable reference reactor antineutrino flux predictions, see the analysis by [Nichols, J. Nucl. Sci. Technol. 52, 17 (2015)]. Various assessments like the one done under the auspices of the [Yoshida et al., Assessment of Fission Product Decay Data for Decay Heat Calculations: A report by the Working Party on International Evaluation Co-operation of the Nuclear Energy Agency Nuclear Science Committee (Nuclear Energy Agency, Organization for Economic Co-operation and Development, Paris, France, 2007), Vol. 25], as well as by [Sonzogni, Johnson, and McCutchan, Phys. Rev. C 91, 011301(R) (2015)] and [Dwyer and Langford, Phys. Rev. Lett. 114, 012502 (2015)], list the A = 142 isobars with high cumulative fission yield among the important nuclei where data for reactor decay heat and/or antineutrino production should be verified and/or improved. Purpose: Our goal is to improve the quality of-decay measurements and evaluate the impact of modified decay schemes on reactor decay heat and antineutrino energy spectra, for fission products along the A = 142 isobaric chain. This work is an in depth follow-up on [Rasco et al., Phys. Rev. Lett. 117, 092501 (2016)]. which presented briefly the impact of the corrected decay scheme of 142Cs. Here, we extend the data to full isobaric decay chain including the daughter nuclei, 142Ba and 142La, and present more details on the 142Cs results. Method: The decays of neutron-rich isobars of mass A = 142 produced by means of proton-induced fission of 238U were measured using the Modular Total Absorption Spectrometer (MTAS) array on-line at the mass separator and Tandem accelerator at Oak Ridge National Laboratory. Results: The-decay schemes for 142Cs and 142La were modified with respect to the nuclear data repositories. A small-delayed neutron branching ratio for 142Cs emitter was remeasured as 0.10+5 -3 %. Improved precision on the measured half-lives is reported. Small corrections to the low-energy decay of 142Ba are made. The-decay patterns for 142La and 142Cs are presented. The decay heat release and cross section for the detection of reactor antineutrinos are deduced and compared to earlier results. Conclusions: The beta-feeding pattern for 142Cs having decay energy value Q beta of over 7 MeV was substantially modified with respect to the current ENSDF entry. Smaller changes were encountered for 142La, but since this A = 142 isobar also has a large cumulative yield in fission, the changes influence both decay heat and the antineutrino spectra. The previously known beta intensities for 142Ba decay (Q beta value of 2.2 MeV) were verified and slightly modified. Overall, increased decay heat values and lower flux of antineutrinos interacting with matter are presented.

Automated summary

The study aims to improve the quality of decay measurements and evaluate the impact of modified decay schemes on reactor decay heat and antineutrino energy spectra. By studying the fission products along the A = 142 isobaric chain, with a focus on the decays of 142Cs, 142Ba, and 142La nuclei, the researchers were able to modify the decay schemes based on experimental measurements and draw conclusions about decay heat release and antineutrino detection cross-sections.