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Nuclear Theory·nucl-th

Tuesday·June 16, 2026

14 papers—3 primary·11 cross-listed

All14Primary3Cross-lists11
  1. 01

    4-momentum conservation as the principal framework for mesonic decay: The case of helium-5-lambda

    Emile Meoto🇨🇲 · Mantile L. Lekala🇿🇦

    Negative-pion and neutral-pion mesonic decays of the hypernucleus He are investigated within two-body and three-body relativistic kinematics in the rest-frame of the hypernucleus. 4-momentum conservation fully constrains the two-body decay, giving rise to a monochromatic pion momentum that is determined through the Newton-Raphson root-finding algorithm. In the case of three-body decay, where 4-momentum conservation is insufficient, the final-state momenta are parametrised by variables whose variations account for all kinematically allowed momenta. A Monte Carlo sampling method is then employed to generate 50 000 decay events per channel that simultaneously satisfy both energy and momentum conservation. The resulting pion momentum distributions exhibit clear peaks at 103.0 MeV/c for neutral pion decay and 97.3 MeV/c for negative pion decay. In addition, only 0.27\% of neutral pion decay events and 0.03\% of negative pion decay events produce nucleons with momenta exceeding the Fermi momentum of He, and are therefore allowed by the Pauli exclusion principle.

    nucl-thAIP Adv.(2026)·2 citations
  2. 02

    Fast-reactor neutron sources in evaluated nuclear data library validation

    Aaron Hurst · Emanuel Chimanski · Toshihiko Kawano · David Brown · David Matters · Lee Bernstein

    Two different neutron sources, based on U-fission neutrons with different average energies, provide integral benchmark data for validation of -ray production data in the evaluated nuclear data libraries corresponding to fast-neutron-induced inelastic-neutron scattering reactions. Firstly, we consider the IRT-M Research Reactor, formerly located at the Nuclear Research Institute just outside of Baghdad, Iraq, to demonstrate the validation methodology using the associated -ray data in the Evaluated Nuclear Data File, version VIII.0 (ENDF/B-VIII.0), for several -ray transitions over a wide range of nuclides including Si, S, Fe, and W. Using the characterized neutron flux of the Baghdad IRT-M Reactor, we find flux-weighted cross-sections deduced using the ENDF/B-VIII.0 -ray data to be in good agreement with the integral measurements performed at the Baghdad Research Reactor in addition to the corresponding results of different reaction-model calculations, {\tt CoH} and {\tt EMPIRE}. Given the excitation thresholds for the -ray transitions involved in this investigation, these observations lend further support to the characterization of the IRT-M flux in the fast-neutron energy region MeV. The additional detail devoted to the IRT-M source reflects the broader scope of the validation work carried out at that facility. A second neutron source considered for this validation work is the Forschungsreaktor Münich (FRM-II), Garching, Germany. Again, the flux-weighted -ray data from ENDF/B-VIII.0 for Fe compare well to the integral FRM-II measurement and reaction-model calculations.

    nucl-thnucl-ex0 citations
  3. 03

    Physics-guided residual correction of -decay half-lives based on the effective liquid drop model

    Qingning Yuan · Xuanpeng Xiao · Panpan Qi · Anqi Yang · Gongming Yu · Haitao Yang · Zhangyan Li · Yanbing Cai

    To improve the prediction accuracy of -decay half-lives in heavy and superheavy nuclei, a physics-guided residual-correction framework combining the effective liquid drop model (ELDM) with machine-learning methods is proposed. The ELDM is first used as the macroscopic baseline for describing the barrier-penetration process, and XGBoost and TabPFN models are then employed to learn the residual deviations between ELDM predictions and experimental data. To incorporate microscopic nuclear-structure information, several physically motivated descriptors are constructed, including deformation-related quantities, Geiger--Nuttall-related features, and minimum orbital angular momentum. The results show that machine-learning residual correction significantly improves the predictive performance of the ELDM baseline. Among all models, TabPFN-term3 achieves the best accuracy, reducing the RMSE and MAE to 0.348 and 0.248, corresponding to improvements of 38.60\% and 40.46\%, respectively. Residual-distribution and feature-ablation analyses further indicate that the corrected predictions are closer to experimental values and that physically motivated descriptors play an important role in learning nonlinear residual structures. Overall, the proposed ELDM-based residual-correction framework can effectively compensate for missing microscopic nuclear-structure effects while preserving physical interpretability, providing a feasible strategy for high-precision -decay half-life prediction.

    nucl-th0 citations

Affiliations

first authorsco-authorsvia INSPIRE