Updated Cross Sections Research Articles

On the Use of the Jacobian-Free Newton Krylov Method to Generate One-Group Discontinuity and Super Homogenization Factors for Full-Core Neutron Diffusion Simulations

Coupled Monte Carlo (MC) and thermal-hydraulic analysis is valuable as a design or reference tool but can be slow, especially when implemented in a Picard iteration. Previous work has developed a novel prediction block to achieve convergence with fewer MC simulations. The prediction works in two stages: (1) a surrogate-like model predicts macroscopic cross sections on the fly and (2) a reduced-order neutronic model predicts the flux response to the updated cross sections. The main challenge with the prediction block is that the reduced-order neutronic model cannot reproduce the spatial flux distribution with high fidelity. This paper investigates the well-established Jacobian-free Newton Krylov (JFNK) method to preserve equivalency between a homogeneous (nodal diffusion) solution and a high-fidelity transport (MC) solution. Instead of performing multiple computationally consuming MC simulations, the nonlinear iterative approach iterates on correction parameters, e.g., assembly discontinuity factors (ADFs) or super homogenization (SPH) factors, using unexpensive nodal solutions. The JFNK approach does not require additional overhead from the MC solver to generate flux tallies. Further, the approach iterates on diffusion solutions produced directly from a desired code, thus ensuring that the parameters are compatible with that code. The approach is applied to correct a nodal diffusion solution for a realistic three-dimensional pressurized water reactor core. The results obtained in the paper show that the method is very successful in reproducing the heterogeneous solution (up to 2.5% difference in assembly flux for SPH and 0.3% for ADFs) without needing to modify the source code of the nodal diffusion solver. In addition, the results show that ADFs yield the best agreement and are also stable (i.e., weakly varying) when thermal-hydraulic fields are perturbed.

The GALPROP Cosmic-ray Propagation and Nonthermal Emissions Framework: Release v57

The past decade has brought impressive advances in the astrophysics of cosmic rays (CRs) and multiwavelength astronomy, thanks to the new instrumentation launched into space and built on the ground. Modern technologies employed by those instruments provide measurements with unmatched precision, enabling searches for subtle signatures of dark matter and new physics. Understanding the astrophysical backgrounds to better precision than the observed data is vital in moving to this new territory. A state-of-the-art CR propagation code, called GalProp, is designed to address exactly this challenge. Having 25 yr of development behind it, the GalProp framework has become a de facto standard in the astrophysics of CRs, diffuse photon emissions (radio to γ-rays), and searches for new physics. GalProp uses information from astronomy, particle physics, and nuclear physics to predict CRs and their associated emissions self-consistently, providing a unifying modeling framework. The range of its physical validity covers 18 orders of magnitude in energy, from sub-keV to PeV energies for particles and from μeV to PeV energies for photons. The framework and the data sets are public and are extensively used by many experimental collaborations and by thousands of individual researchers worldwide for interpretation of their data and for making predictions. This paper details the latest release of the GalProp framework and updated cross sections, further developments of its initially auxiliary data sets for models of the interstellar medium that grew into independent studies of the Galactic structure—distributions of gas, dust, radiation, and magnetic fields—as well as the extension of its modeling capabilities. Example applications included with the distribution illustrating usage of the new features are also described.

Path to Increasing p-B11 Reactivity via ps and ns Lasers

The Lawson criterion for proton-boron (p-11B) thermonuclear fusion is substantially higher than that for deuterium-tritium (DT) because the fusion cross section is lower and peaks at higher ion energies. The Maxwellian averaged p-11B reactivity peaks at several hundred keV, where bremsstrahlung radiation emission may dominate over fusion reactions if electrons and ions are in thermal equilibrium and the losses are unrestricted. Nonequilibrium burn has often been suggested to realize the benefits of this aneutronic reaction, but the predominance of elastic scattering over fusion reactivity makes this difficult to achieve. The development of ultrashort pulse lasers (USPL) has opened new possibilities for initiating nonequilibrium thermonuclear burns and significant numbers of p-11B alpha particles have been reported from several experiments. We present an analysis that shows that these significant alpha yields are the result of beam fusion reactions that do not scale to net energy gain. We further find that the yields can be explained by experimental parameters and recently updated cross sections such that a postulated avalanche mechanism is not required. We use this analysis to understand the underlying physics of USPL-driven nonequilibrium fusion reactions and whether they can be used to initiate fusion burns. We conclude by outlining a path to increasing the p-11B reactivity towards the goal of achieving ignition and describing the design principles that we will use to develop a computational point design.

Implications of current nuclear cross sections on secondary cosmic rays with the upcoming DRAGON2 code

Current measurements of cosmic-ray fluxes have reached unprecedented accuracy thanks to the new generation of experiments, and in particular the AMS-02 mission. At the same time, significant progress has been made in the propagation models of galactic cosmic rays. These models include several propagation parameters, which are usually inferred from the ratios of secondary to primary cosmic rays, and which depend on the cross sections describing the collisions among the various species of cosmic-ray nuclei. At present, our knowledge of these cross sections in the energy range where cosmic-ray interactions occur is limited, and this is a source of uncertainties in the predicted fluxes of secondary cosmic-ray nuclei. In this work we study the impact of the cross section uncertainties on the fluxes of light secondary nuclei (Li, Be, B) using a preliminary version of the upcoming DRAGON2 code. We first present a detailed comparison of the secondary fluxes computed by implementing different parameterizations for the network of spallation cross sections. Then, we discuss the use of secondary-over-secondary cosmic-ray flux ratios as a tool to improve the consistency of cross sections parameterizations and give insight of the overall uncertainties coming from the cross sections parametrisations. We show that the uncertainties inferred from the cross section data are enough to explain the discrepancies in the Be and Li fluxes with respect to the AMS-02 data, with no need of a primary component in their spectra. In addition, we show that the fluxes of B, Be and Li can be simultaneously reproduced by rescaling their cross sections within the experimental uncertainty. Finally, we also revisit the diffusive estimation of the halo size, obtaining good agreement with previous works and a best fit value of 6.8 ± 1 kpc from the most updated cross sections parametrisations.

High-multiplicity muon events observed with EMMA array

High-multiplicity data, collected with a segmented scintillator array of the cosmic-ray experiment EMMA (Experiment with Multi-Muon Array), is presented for the first time. The measurements were done at the depth of 75 meters (210 m.w.e.) in the Pyhäsalmi mine in Finland. EMMA uses two types of detectors: drift chambers and plastic scintillation detectors. The presented data were acquired over the period between December, 2015 and April, 2018 using 128-800 plastic scintillator pixels probing the fiducial area of ˜100 m2. The results are being interpreted in terms of CORSIKA simulations. Several events with densities in excess of 10 muons per m2 were observed. At the next stage of the analysis, the high-multiplicity events will be matched with precision tracking data extracted from the multi-layer drift chambers of EMMA. Observation of high-density muon bundles was first reported by the LEP experiments: DELPHI, L3+C, and ALEPH. More recently, the ALICE experiment at CERN has provided new cosmic-ray results together with improved interpretation benefiting from the updated cross section values extracted from LHC results. While the tracking performance of ALICE is superior to EMMA, the duration of ALICE cosmic-ray measurements is very limited. Over the period of 2010–2018 the total exposure was only 93 days while EMMA, having a similar overburden provides a larger footprint and collects data continuously.

Neutralino-chargino pair production at NLO+NLL with resummation-improved parton density functions for LHC Run II

We make use of recently released parton density functions (PDFs) with threshold-resummation improvement to consistently calculate theoretical predictions for neutralino and chargino pair production at next-to-leading order and next-to-leading logarithmic accuracy. The updated cross sections have been computed for experimentally relevant higgsino and gaugino search channels at the ongoing Run II of the LHC. A factorisation method is applied to exploit the smaller PDF uncertainty of the global PDF sets and to avoid complications arising in the refitting of threshold-resummation improved PDF replicas in Mellin space. The reduction of the scale uncertainty due to the resummation is, however, explicitly taken into account. As expected, the resummation contributions in the PDF fits partially compensate the cross section enhancements induced by those in the partonic matrix elements.

Total Ambient Dose Equivalent Buildup Factor Determination for Nbs04 Concrete.

Buildup factors are dimensionless multiplicative factors required by the point kernel method to account for scattered radiation through a shielding material. The accuracy of the point kernel method is strongly affected by the correspondence of analyzed parameters to experimental configurations, which is attempted to be simplified here. The point kernel method has not been found to have widespread practical use for neutron shielding calculations due to the complex neutron transport behavior through shielding materials (i.e. the variety of interaction mechanisms that neutrons may undergo while traversing the shield) as well as non-linear neutron total cross section energy dependence. In this work, total ambient dose buildup factors for NBS04 concrete are calculated in terms of neutron and secondary gamma ray transmission factors. The neutron and secondary gamma ray transmission factors are calculated using MCNP6™ code with updated cross sections. Both transmission factors and buildup factors are given in a tabulated form. Practical use of neutron transmission and buildup factors warrants rigorously calculated results with all associated uncertainties. In this work, sensitivity analysis of neutron transmission factors and total buildup factors with varying water content has been conducted. The analysis showed significant impact of varying water content in concrete on both neutron transmission factors and total buildup factors. Finally, support vector regression, a machine learning technique, has been engaged to make a model based on the calculated data for calculation of the buildup factors. The developed model can predict most of the data with 20% relative error.

Improving activation cross section data with TALYS

Needs for accurate (n,x) activation cross sections for fusion technology have been considered with reference to the current status of the TENDL library. The current work is focused on improving activation cross section data for nuclear reactions relevant mainly for fusion and astrophysical needs. The fits have been performed with the TALYS-1.8 code by means of nuclear model parameter variation, mostly for the optical model and level densities, followed by comparison to recent experimental data taken from EXFOR and other evaluated nuclear databases. The updated cross section data are going to be adopted into the new version of TENDL. The improvements have been performed both for differential as well as integral data sets.

Application of the SAMINT methodology to the new cross section evaluations of63Cu and65Cu∗

The SAMINT methodology allows coupling of differential and integral data evaluations in a continuous-energy framework. Prior to development of the SAMINT code, integral experimental data such as in the International Criticality Safety Benchmark Experiments Project remained a tool for validation of completed nuclear data evaluations. Now, SAMINT extracts information from integral benchmarks in the form of calculated sensitivity coefficients by Monte Carlo codes such as CE TSUNAMI-3D or MCNP6 and combines it with the results of experimental cross section measurements to produce an updated cross section evaluation utilizing information from both sets of data. The use of the generalized linear least squares methodology ensures that proper weight is given to both the differential and integral data. SAMINT is not intended to bias nuclear data toward specific integral experiments, but it should be used to supplement evaluation of differential experimental data. This work demonstrates the application of the SAMINT methodology to the new Oak Ridge National Laboratory (ORNL) evaluations of the resonance parameters for two isotopes of copper: 63 Cu and 65 Cu.

The Impact of Updated Cross Section Libraries on ITER Neutronics Calculations

In ITER, determination of radiation loads such as nuclear heating due to neutrons and photons (gammas) is an important part of the design process. Monte Carlo transport codes need accurate neutron and photon cross section libraries to produce accurate results. Because photon heating dominates the contribution to total nuclear heating for common materials like stainless steel and copper in several key components of ITER, the photon cross section library is particularly important. In this work, two ITER realistic benchmark calculation models are used to determine the impact on nuclear heating by the cross section library used in the calculation. The results show that the nuclear heating can be as much as 5% lower to as much as 6% higher than the nuclear heating calculated using the standard fusion neutron and photon cross section library.

Determination of equilibrium electron temperature and times using an electron swarm model with BOLSIG+ calculated collision frequencies and rate coefficients

AbstractElectromagnetic pulse (EMP) events produce low‐energy conduction electrons from Compton electron or photoelectron ionizations with air. It is important to understand how conduction electrons interact with air in order to accurately predict EMP evolution and propagation. An electron swarm model can be used to monitor the time evolution of conduction electrons in an environment characterized by electric field and pressure. Here a swarm model is developed that is based on the coupled ordinary differential equations (ODEs) described by Higgins et al. (1973), hereinafter HLO. The ODEs characterize the swarm electric field, electron temperature, electron number density, and drift velocity. Important swarm parameters, the momentum transfer collision frequency, energy transfer collision frequency, and ionization rate, are calculated and compared to the previously reported fitted functions given in HLO. These swarm parameters are found using BOLSIG+, a two term Boltzmann solver developed by Hagelaar and Pitchford (2005), which utilizes updated cross sections from the LXcat website created by Pancheshnyi et al. (2012). We validate the swarm model by comparing to experimental effective ionization coefficient data in Dutton (1975) and drift velocity data in Ruiz‐Vargas et al. (2010). In addition, we report on electron equilibrium temperatures and times for a uniform electric field of 1 StatV/cm for atmospheric heights from 0 to 40 km. It is shown that the equilibrium temperature and time are sensitive to the modifications in the collision frequencies and ionization rate based on the updated electron interaction cross sections.

Calculation of beams of positrons, neutrons, and protons associated with terrestrial gamma ray flashes

AbstractPositron beams have been observed by the Fermi satellite to be correlated with lightning leaders, and neutron emissions have been attributed to lightning and to laboratory sparks as well. Here we discuss the cross sections to be used for modeling these emissions, and we calculate the emissions of positrons, neutrons, and also protons from lightning leaders. Neutrons were first erroneously attributed to fusion reactions, but the photonuclear reaction responsible for neutrons should create protons as well. We predict them here; they have not been observed yet. In the paper, we first revisit the model for stepped lightning leaders of Xu, Celestin, and Pasko with updated cross sections, we analyze the spatial and energetic structure of the electron beam, and we calculate the spectrum of the generated gamma ray beam at 16 km altitude. Then we review the scattering processes of photons with emphasis on the processes above 5 MeV, in particular the photon energy losses in Compton scattering events and the generation of leptons and hadrons. We provide simple approximations for photon energy loss and lepton and hadron production for any photon with energy above 5 MeV passing through an arbitrary air layer. Finally, we launch a gamma ray beam with the earlier calculated spectrum of the negative stepped lightning leader from 16 km upward and calculate the production and energy of positrons, neutrons, and protons as well as the propagation of positrons.

Phenomenology of the $ppK^+K^-$ System Near Threshold

In this article studies of the near threshold $pp\to ppK^+K^-$ reaction conducted with the COSY-11 and the ANKE detectors are reviewed. In particular recent investigations on the $K^+K^-$ final state interaction are revisited taking into account updated cross sections of the COSY-11 experiment. These studies resulted in the new value of $K^+K^-$ effective range amounting to: $\mathrm{Re}(b_{K^{+}K^{-}}) = -0.2^{+0.8_{stat}~+0.4_{sys}}_{-0.6_{stat}~-0.4_{sys}}~\mathrm{fm}$ and $\mathrm{Im}(b_{K^{+}K^{-}}) = 1.2^{~+0.5_{stat}~+0.3_{sys}}_{~-0.3_{stat}~-0.3_{sys}}~\mathrm{fm}$. The determined real and imaginary parts of the $K^+K^-$ scattering length were estimated to be: $\left|\mathrm{Re}(a_{K^{+}K^{-}})\right| = 10^{~+17_{stat}}_{~-10_{stat}}~\mathrm{fm}$ and $\mathrm{Im}(a_{K^{+}K^{-}}) = 0^{~+37_{stat}}_{~-10_{stat}}~\mathrm{fm}$.

Gain analysis of proton–lithium pellets at inertial confinement fusion with volume ignition

The possibility of volume ignition of proton–lithium (p–7Li) with negligible radioactivity has encouraged us to study the fusion of compressed solid state p–7Li fuel. It is shown that volume ignition of p–7Li reaction happens at compressions one hundred times more than that of deuterium–tritium (D–T) reaction. This may lead to densities higher than 105 times the solid-state density. In this paper, updated cross sections of the fusion reaction are included. The optimum gain is analyzed and retrograde behavior gains are investigated. Similar to hydrogen–boron (p–11B) fuel, threshold energy required for igniting this fuel is within the range of giga joule (GJ). But due to higher energy of alpha particles, retrograde behavior of p–7Li is weaker in comparison with p–11B.

CO Cameron band and UV doublet emissions in the dayglow of Venus: Role of CO in the Cameron band production

The present study deals with the model calculations of CO Cameron band and ultraviolet doublet emissions in the dayglow of Venus. The overhead and limb intensities of CO Cameron band and UV doublet emissions are calculated for low, moderate, and high solar activity conditions. Using updated cross sections, the impact of different e‐CO cross sections for Cameron band production is estimated. The electron impact on CO is the major source mechanism of Cameron band, followed by electron and photon impact dissociation of CO2. The overhead intensities of CO Cameron band and UV doublet emissions are about a factor of 2 higher in solar maximum than those in solar minimum condition. The effect of solar EUV flux models on the emission intensity is ∼30–40% in solar minimum condition and ∼2–10% in solar maximum condition. At the altitude of emission peak (∼135 km), the model predicted limb intensity of CO Cameron band and UV doublet emissions in moderate (F10.7=130) solar activity condition is about 2400 and 300 kR, respectively, which is in agreement with the very recently published SPICAV/Venus Express observation. The model limb intensity profiles of CO Cameron band and UV doublet are compared with SPICAV observation. We also calculated intensities of N2Vegard‐Kaplan UV bands and O I 2972 Å emissions during moderate and high solar activity conditions.

Stratospheric loss and atmospheric lifetimes of CFC-11 and CFC-12 derived from satellite observations

Abstract. The lifetimes of CFC-11 and CFC-12 have been evaluated using global observations of their stratospheric distributions from satellite-based instruments over the time period from 1992 to 2010. The chlorofluorocarbon (CFC) datasets are from the Cryogen Limb Array Etalon Spectrometer (CLAES), the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA-1 and CRISTA-2), the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), and the Atmospheric Chemistry Experiment (ACE). Stratospheric loss rates were calculated using an ultraviolet radiative transfer code with updated cross section and solar irradiance data. Mean steady-state lifetimes based on these observations are 44.7 (36–58) yr for CFC-11 and 106.6 (90–130) yr for CFC-12, which are in good agreement with the most recent WMO ozone assessment. There are two major sources of error in calculating lifetimes using this method. The first important error arises from uncertainties in tropical stratospheric observations, particularly for CFC-11. Another large contribution to the error is due to uncertainties in the penetration of solar ultraviolet radiation at wavelengths between 185 and 220 nm, primarily in the tropical stratosphere between 20 and 35 km altitude.

Heavy Flavour and Quarkonium Production at the LHC

Recent results on heavy flavour and quarkonium production, obtained by ATLAS, CMS and LHCbusing data from the 2011 and 2012 pp runs, are summarised. They include J/ψ and ψ′ ϒ cross sections andpolarizations, as well as the first prompt X(3872) differential cross section. Results in the heavy flavour sectorinclude an updated cross section measurement differential in the separation between two b-tagged jets. Somefirst measurements atps √s = 8 TeV are also shown.

Higgs production at the LHC: Updated cross sections at [formula omitted

We present predictions for the inclusive cross section for Higgs boson production by gluon–gluon fusion in proton collisions at s=8 TeV. Our calculation is accurate up to next-to-next-to-leading order in QCD perturbation theory and includes soft-gluon effects up to next-to-next-to-leading logarithmic accuracy and two-loop electroweak corrections. The dependence on heavy-quark masses is taken into account exactly up to next-to-leading order and next-to-leading logarithmic accuracy, and a treatment of the Higgs boson line-shape is provided according to the complex-pole scheme.

THE PRODUCTION OF LOW-ENERGY NEUTRONS IN SOLAR FLARES AND THE IMPORTANCE OF THEIR DETECTION IN THE INNER HELIOSPHERE

Neutron detectors on spacecraft in the inner heliosphere can observe the low-energy (<30 MeV) solar-flare neutrons that are not easily observable at Earth because they are lost to decay during transit. We present calculations of low-energy neutron production using a computer code incorporating updated neutron-production cross sections for the proton and {alpha}-particle reactions with heavier elements at all ion energies, especially at low energies (E{sub ion} < 10 MeV nucleon{sup -1}) most important for producing low-energy neutrons from these reactions. We calculate escaping-neutron spectra and neutron-capture line yields from ions propagating in a magnetic loop with various kinetic-energy spectra. This study provides the basis for planning inner-heliospheric missions having a low-energy neutron detector. The MESSENGER spacecraft orbiting Mercury has such a detector. We conclude that a full understanding of ion acceleration, transport, and interaction at the Sun requires observation of both neutrons and gamma rays with detectors of comparable sensitivity. We find that the neutron-capture line fluence at 1 AU is comparable to the 1-10 MeV neutron fluence at 0.5 AU, and therefore as effective for revealing low-energy ion acceleration. However, as the distance from the Sun to the neutron detector decreases, the tremendous increase of the low-energy neutron fluxmore » allows exploration of ion acceleration in weak flares not previously observable and may reveal acceleration at other sites not previously detected where low-energy neutrons could be the only high-energy signature of ion acceleration. Also, a measurement of the low-energy neutron spectrum will provide important information about the accelerated-ion spectrum that is not available from the capture line fluence measurement alone.« less

Candidates for Laser Fusion Energy with Minimized Radioactivity

The new candidates for laser fusion energy with minimized radioactivity were presented. The possibility of side-on laser ignition of H–11B with negligible radioactivity encouraged to study the fusion of solid state H–7Li fuel which again turns out to be only about ten times more difficult than the side-on ignition of solid deuterium–tritium using petawatt-picosecond laser pulses at anomalous interaction conditions if very high contrast ratio. Updated cross sections of the nuclear reaction are included. In other words, the specific approach discussed here involves inducing a fusion burn wave without radioactivity by laser-driven impact of a relatively large block of plasma on the outside of a solid density H–11B and H–7Li targets.