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The performance of neutron transport calculations is heavily reliant on the fidelity of nuclear data. The Free Gas Model (FGM) is no longer applicable at low neutron energy range due to nucleus binding effects, necessitating the implementation of the Thermal Scattering Law (TSL). The present study systematically reports the unexpected discrepancies in keff calculations with TSL across different versions of OpenMC, an open-source Monte Carlo code developed by MIT. Based on four representative benchmark series (HMT-026, HMT-027, BEAVRS, and TRIGA fuel rod), the analysis reveals that updates in OpenMC v0.13.0 significantly contribute to these discrepancies, sometimes up to ~1000 pcm. After further review, a modification in the source code for coherent elastic scattering (suggestion #1949) may affect the sampling of the cosine of the coherent scattering angle. Additionally, recompilation of OpenMC v13.2 using the older segment code aligns reactivity calculations closely with version 0.12.2 and thus confirms the above conclusion. Nevertheless, both the developers and we are still uncertain whether this update is correct until now. A systematic examination of the source code is necessary in the near future. Another direct conclusion from the present study is the importance of including diverse benchmarks for code verification and validation.

NJOY is the only open-source nuclear data processing code allowing calculating neutron-induced displacement damage cross sections from evaluated nuclear data. However, some issues exist in the NJOY calculation of damage cross sections, including the inconsistency for neutron capture reaction with photon data given in MF6 vs. MF12-MF15, questionable or even incorrect recoil nuclear data in MF6, discrepant damage cross sections using different approaches, and the potential underestimation above 20 MeV due to the storage of nuclear data in MT5. These issues should be addressed by the improvements on both evaluated nuclear data and the NJOY code.

ObjectivesTo explore the suicide risk-specific disruption of cortical hierarchy in major depressive disorder (MDD) patients with diverse suicide risks.MethodsNinety-two MDD patients with diverse suicide risks and 38 matched controls underwent resting-state functional MRI. Connectome gradient analysis and stepwise functional connectivity (SFC) analysis were used to characterize the suicide risk-specific alterations of cortical hierarchy in MDD patients.ResultsRelative to controls, patients with suicide attempts (SA) had a prominent compression from the sensorimotor system; patients with suicide ideations (SI) had a prominent compression from the higher-level systems; non-suicide patients had a compression from both the sensorimotor system and higher-level systems, although it was less prominent relative to SA and SI patients. SFC analysis further validated this depolarization phenomenon.ConclusionThis study revealed MDD patients had suicide risk-specific disruptions of cortical hierarchy, which advance our understanding of the neuromechanisms of suicidality in MDD patients.

ObjectiveInter-hemispheric network dysconnectivity has been well-documented in patients with recurrent major depressive disorder (MDD). However, it has remained unclear how structural networks between bilateral hemispheres relate to inter-hemispheric functional dysconnectivity and depression severity in MDD. Our study attempted to investigate the alterations in corpus callosum macrostructural and microstructural as well as inter-hemispheric homotopic functional connectivity (FC) in patients with recurrent MDD and to determine how these alterations are related with depressive severity.Materials and MethodsResting-state functional MRI (fMRI), T1WI anatomical images and diffusion tensor MRI of the whole brain were performed in 140 MDD patients and 44 normal controls matched for age, sex, years of education. We analyzed the macrostructural and microstructural integrity as well as voxel-mirrored homotopic functional connectivity (VMHC) of corpus callosum (CC) and its five subregion. Two-sample t-test was used to investigate the differences between the two groups. Significant subregional metrics were correlated with depression severity by spearman's correlation analysis, respectively.ResultsCompared with control subjects, MDD patients had significantly attenuated inter-hemispheric homotopic FC in the bilateral medial prefrontal cortex, and impaired anterior CC microstructural integrity (each comparison had a corrected P < 0.05), whereas CC macrostructural measurements remained stable. In addition, disruption of anterior CC microstructural integrity correlated with a reduction in FC in the bilateral medial prefrontal cortex, which correlated with depression severity in MDD patients. Furthermore, disruption of anterior CC integrity exerted an indirect influence on depression severity in MDD patients through an impairment of inter-hemispheric homotopic FC.ConclusionThese findings may help to advance our understanding of the neurobiological basis of depression by identifying region-specific interhemispheric dysconnectivity.

The relativistic effect on two-body discrete reaction inducing atomic recoil energy and the sequent damage energy is studied for 6Li, 56Fe, 184W, and 238U. The relativistic correction is within 1% if incident neutron energy is below 20 MeV. For incident neutron energy up to 200 MeV or even 800 MeV, the relativistic effect should be taken into account for treating two-body kinematics. The relativistic correction is about 0.05Ein/MeV% for neutron elastic scattering for nuclei from 56Fe to 238U and smaller for (n,α) and (n,t) reactions. Analyses on damage energy show that the relativistic corrections are generally within 2% for incident neutron below 200 MeV for nuclei lighter than 56Fe because of the “saturation” of damage energy. However, the current damage theory cannot be applied for Primary Knock-on Atom (PKA) energy higher than 24.9ARZR4/3 keV, which is 10 times lower than the maximum PKA energy for D+T fusion neutron elastic scattering of 6Li.

Neutron-induced cross section is one of the key quantities in nuclear physics and nuclear engineering. The integral experiment can give good feedback to the cross sections with low uncertainties. Using the optical model and statistical model, the neutron-induced total and capture cross sections of153Eu are revaluated according to the experimental microscopic total cross sections and the PROFIL-2 integral experiment. The corresponding uncertainties and covariances are determined with the data assimilation method implemented in CONRAD code. On the other hand, the previous interpretation of the PROFIL-2 experiment showed that JEFF-3.1 overestimates the neutron-induced capture cross section of 151 Eu by a factor of 2. Further analysis performed in the present work points out that the large difference between calculation and experimental data is mainly due to the lack of152m1 Eu in ERANOS code, which was used to interpret the PROFIL-2 experiment. The correction of 152m1Eu on the interpretation largely reduces the difference between JEFF-3.1 and PROFIL-2 and shows the agreement between the PROFIL-2 integral experiment and other microscopic measurements. The revaluated neutron-induced total and capture cross sections of 151 Eu and 153Eu correspond well with both the microscopic experimental measurements and the PROFIL-2 integral experiment.

Atomic displacement is one of the key factors that influence the behaviors of material properties during and after irradiation. Many models, including the international standard metric Norgett-Robinson-Torrens model (NRT), have been developed to calculate the number of Displacement per Atom (DPA) using the energy of Primary Knocked-on Atom (PKA) as a major parameter. However, extensive experiments and simulations indicate that the NRT-DPA model seriously overestimates (about 3 times) the actual DPA. Nordlund recently developed the Athermal Recombination-Corrected DPA (ARC-DPA) model, which shows that the Molecular Dynamics (MD) simulations can be directly used to compute DPA by fitting the simulated data for each isotope. The present work proposes a simpler expression for the efficiency function to calculate the DPA without requiring fitting parameters as needed in the ARC-DPA model. Our DPA calculation results utilizing the improved efficiency function are validated against the experimental data for the Fe, Ni, Cu, and Ag. The applications in fast breeder nuclear reactors show good agreement with the ARC-DPA metric for 56Fe.

Correlations between neutron inelastic scatterings angular distributions are not included in the Joint Evaluated Fission and Fusion (JEFF) nuclear data library, while they are key quantities for uncertainty propagation of nuclear data. By reproducing the angle-integrated cross sections and uncertainties of JEFF-3.1.1, the present work obtains covariance matrix between high energy model parameters using the least square method implemented in the CONRAD code. With this matrix, it is possible to generate correlations between angle-integrated cross sections and angular distributions, which are usually presented by Legendre coefficients. As expected, strong correlations are found, for example, between the Legendre coefficients of elastic and first-level-inelastic scatterings and the angle-integrated total, elastic, total inelastic cross sections.