Predictions of antineutrino fluxes produced by fission isotopes in a nuclear reactor have recently received increased scrutiny due to observed differences in predicted and measured inverse beta decay (IBD) yields, referred to as the "reactor antineutrino flux anomaly." In this paper, global fits are applied to existing IBD yield measurements to produce constraints on antineutrino production by individual plutonium and uranium fission isotopes. We find that fits including measurements from highly 235 U-enriched cores and fits including Daya Bay's new fuel evolution result produce discrepant bestfit IBD yields for 235 U and 239Pu. This discrepancy can be alleviated in a global analysis of all data sets through simultaneous fitting of 239 Pu, 235 U, and 238 U yields. The measured IBD yield of 238 U in this analysis is ð7.02 AE 1.65Þ × 10 −43 cm 2 =fission, nearly two standard deviations below existing predictions. Future hypothetical IBD yield measurements by short-baseline reactor experiments are examined to determine their possible impact on the global understanding of isotopic IBD yields. It is found that future improved short-baseline IBD yield measurements at both high-enriched and low-enriched cores can significantly improve constraints for 235 U, 238 U, and 239 Pu, providing comparable or superior precision to existing conversion-and summation-based antineutrino flux predictions. Systematic and experimental requirements for these future measurements are also investigated.

A : PROSPECT, the Precision Reactor Oscillation and SPECTrum experiment, is a short-baseline reactor antineutrino experiment designed to provide precision measurements of the 235 U product ν e spectrum, utilizing an optically segmented 4-ton liquid scintillator detector. PROSPECT's segmentation system, the optical grid, plays a central role in reconstructing the position and energy of ν e interactions in the detector. This paper is the technical reference for this PROSPECT subsystem, describing its design, fabrication, quality assurance, transportation and assembly in detail. In addition, the dimensional, optical and mechanical characterizations of optical grid components and the assembled PROSPECT target are also presented. The technical information and characterizations detailed here will inform geometry-related inputs for PROSPECT physics analysis, and can guide a variety of future particle detection development efforts, such as those using optically reflecting materials or filament-based 3D printing.