Thermal Cross Section Research Articles

Gamma-ray signal from ZN≥3 dark matter-companion models

In Ref. [10], we proposed to replace the final dark matter (DM) particle in the semi-annihilation mode DM+DM→antiDM+Higgs boson with its ZN≥3 companion, thus reducing DM number density without DM-nucleon scattering. In this work, we study the indirect detection signals from DM annihilation, the Higgs boson pair with one of them from the companion decay being on- or off- shell, depending on the DM-companion mass splitting. We generate the photon spectrum by using PYTHIA8 and study the properties of the spectrum, to find that the hard part of the spectrum in our model is mainly shaped by the direct Higgs boson and thus does not differ much from that of the conventional semi-annihilation mode. Using the Fermi-LAT data of dwarf spheroidal galaxies, we derive the current limit of the DM annihilation cross section for DM+DM→companion⁎+Higgs boson, and for the relatively light DM, it reaches the typical thermal cross section. However, for the TeV scale DM, we have to rely on the Cherenkov Telescope Array, which is able to rule out the whole parameter space except for the coannihilation region.

Gamma rays from dark matter spikes in EAGLE simulations

Intermediate Mass Black Holes (IMBHs) with a mass range between 100 M⊙ and 106 M⊙ are expected to be surrounded by high dark matter densities, so-called dark matter spikes.The high density of self-annihilating Weakly Interacting Massive Particles (WIMPs) in these spikes leads to copious gamma-ray production. Sufficiently nearby IMBHs could therefore appear as unidentified gamma-ray sources.However, the number of IMBHs and their distribution within our own Milky Way is currently unknown. In this work, we provide a mock catalogue of IMBHs and their dark matter spikes obtained from the EAGLE simulations, in which black holes with a mass of 105 M⊙/h are seeded into the centre of halos greater than 1010 M⊙/h to model black hole feedback influencing the formation of galaxies.The catalogue contains the coordinates and dark matter spike parameters for about 2500 IMBHs present in about 150 Milky Way-like galaxies. We expect about 15+9 -6 IMBHs within our own galaxy, mainly distributed in the Galactic Centre and the Galactic Plane. In the most optimistic scenario, we find that current and future gamma-ray observatories, such as Fermi-LAT, H.E.S.S. and CTAO, would be sensitive enough to probe the cross section of dark matter self-annihilation around IMBHs down to many orders of magnitude below the thermal relic cross section for dark matter particles with masses from GeV to TeV.We have made the IMBH mock catalogue and the source code for our analysis publicly available, providing the resources to study dark matter self-annihilation around IMBHs with current and upcoming gamma-ray observatories.

NLO thermal corrections to dark matter annihilation cross sections: A novel approach

Dark matter relic density has been increasingly accurately measured by successive generations of experiments. The Boltzmann equation determines the yields using the dark matter annihilation cross section as one of the inputs; the accurate computation of the latter including thermal contributions thus assumes importance. We report here the next-to-leading-order (NLO) thermal corrections to the cross sections for (Majorana) dark matter annihilation of standard model fermions, χχ→ff¯, via charged scalars. We use a novel approach, utilizing the technique of Grammer and Yennie, extended to thermal field theories, where the cancellation of soft infrared divergences occurs naturally. We present the NLO thermal cross sections in full detail both for the relativistic case and in the nonrelativistic limit. Our independent calculation verifies earlier results where the leading contribution at order O(T2) was shown to be proportional to the square of the fermion mass in the nonrelativistic limit, just as at leading order. We find that the O(T4) contributions have the same dependence on the fermion mass as well. Published by the American Physical Society 2024

Improved constraints on dark matter annihilations around primordial black holes

Cosmology may give rise to appreciable populations of both particle dark matter and primordial black holes (PBH) with the combined mass density providing the observationally inferred value ΩDM ≈ 0.26. Early studies highlighted that scenarios with both particle dark matter and PBH are strongly excluded by γ-ray limits for particle dark matter with a velocity independent thermal cross section 〈σν〉 ~ 3 × 10−26cm3/s, as is the case for classic WIMP dark matter. Here we examine the limits from di use γ-rays on velocity-dependent, including annihilations which are p-wave with 〈σν〉 ∝ v2 or d-wave 〈σν〉 ∝ v4, which we find to be considerably less constraining. This work also utilizes a refined treatment of the PBH dark matter density profile. Importantly, we highlight that even if the freeze-out process is p-wave it is typical for (loop/phase-space) suppressed s-wave processes to actually provide the leading contributions to the experimentally constrained γ-ray flux from the PBH halo.

Accident tolerant fuel design optimization for SMART reactor

Fully Ceramic Microencapsulated (FCM) fuel is one of the most advancedfuel types for the next nuclear reactor generations. The use of uranium carbide fuel in FCM offers multiple benefits such as high fuel density, improved thermal conductivity and enhanced mechanical stability. Both UC and conventional fuel (UO2) have the same melting point. As a result, under reactor operating conditions, UC has better safety margins. In addition, FeCrAl is a promising cladding material. However, because of its greater thermal neutron absorption cross section, FeCrAl has a neutronic penalty when compared to Zircaloy leading to an annual reload requirement with high fuel enrichment. Owing to their low power density and excellent design, small modular reactors (SMRs) have exceptional inherent safety. In this work, we determined the optimum design of an accident tolerant fuel (ATF), with respect to neutronics, in SMART reactor using dense UC FCM (in contrast to the conventional UO2 fuel) and a combination of zircalloy and FeCrAl (FCM -Zircaloy, FCM -FeCrAl, FCM -combining of zircaloy and FeCrAl) as cladding to achieve better thermal conductivity as well as safer performance, while considering the required fuel enrichment for the proposed designs. The effective multiplication factor and burnup were calculated for neutronic assessment of the SMART core, the outcomes are showcased alongside a comprehensive assessment of the characteristics and prospective. The neutronic parameters were estimated using the stochastic MCNPX 2.6 code. We found that Fully Ceramic Microencapsulated -Uranium Carbide (FCM-UC) fuel type was more attractive than conventional UO2. The optimum cladding design as compared to the reference case and the other cases of (FCM-UC), was determined. When 50% FeCrAl cladding was employed, case 15 in our study emerged as the superior design, demonstrating maximum production of 239Pu due to higher initial concentrations of 235U and quantities of 238U. This work may offer recommendations for future optimized designs of the SMART reactor parameters.

Minimal mass of thermal dark matter and the viability of millicharged particles affecting 21-cm cosmology

Thermal freeze-out offers an attractive explanation of the dark matter density free from fine-tuning of initial conditions. For dark matter with a mass below tens of MeV, photons, electrons, and neutrinos are the only available direct Standard Model annihilation products. Using a full three-sector abundance calculation, we determine the minimal mass of dark matter, allowing for an arbitrary branching into electrons/photons and neutrinos that is compatible with current cosmological observations. The analysis takes into account the heat transfer between the various sectors from annihilation elastic scattering, representing the first fully self-consistent analysis that tracks the respective sectors’ temperatures. We thereby provide accurate thermal annihilation cross sections, particularly for velocity-dependent cases, and deduce the sensitivity of current and upcoming CMB experiments to MeV thermal dark matter. In the latter context, we also establish the fine-tuned parameter region where a tiny admixture of neutrinos in the final states rules in MeV-scale p-wave annihilating DM into electrons. Finally, we show that a sub-% millicharged dark matter with an interaction strength that interferes with 21-cm cosmology is still allowed when freeze-out is supplemented with annihilation into neutrinos. For all cases considered, we provide concrete particle physics models and supplement our findings with a discussion of other relevant experimental results. Published by the American Physical Society 2024

Investigation of the Cd-Ratio difference method to measure the cross section of 186W(n,γ)187W at the Jordan Research and Training reactor

The neutron capture cross section of 186W(n,γ)187W was measured at different energies, including the thermal capture cross section (0.025 eV) and resonance integral. Neutron capture cross section values were determined using the activation technique and by applying the Cadmium-ratio difference method. Two irradiation locations at the Jordan Research and Training Reactor (JRTR) were used (NAA1 and NAA2). The thermal capture cross section values were determined to be 39.56 ± 0.69 ± 2.58b and 32.17 ± 3.72 ± 2.00b at NAA1 and NAA2, respectively. While resonance integral values were found to be 113.93 ± 8.20 ± 16.87b and 69.35 ± 26.63 ± 29.69b at NAA1 and NAA2, respectively. The present results of the resonance integral are not in good agreement with the most of the previous experimental and evaluated data as well as the theoretical calculations.

Reexamination of a 40Ca(n,α)37Ar cross section measurement from existing literature

Background 37Ar, produced from the neutron activation of 40Ca in sub-surface rock and soil, is important for nuclear explosion monitoring. Most of the cross section measurements done for the 40Ca(n,α) 37 Ar reaction are in the fast neutron region. A thermal cross section measurement was attempted in 1989, with the assumption that the 4-8 MeV neutrons would be completely thermalized with 8-cm of water. Methods The experimental setup was modeled using Monte Carlo N-Particle code to see if the assumptions for the neutron distribution were accurate. A model of a 3.0 MeV deuteron source was used to recreate the neutron source from the experiment. Additional modeling was done using SCALE to compare the predictions of 37Ar yields when using the measured cross section from 1989 compared to current nuclear data models. Results Modeling showed the neutron distribution was closer to 10% thermal and 90% fast as opposed to entirely thermalized. The additional modeling showed how the overestimation of the thermal cross section would affect the predicted yield of 37Ar. Conclusions Based on the modeling results, the assumption that all the 4-8 MeV neutrons are thermalized with 8-cm of water is not accurate. The high fraction of fast neutrons interacting with the Ca will result in an overestimation of the thermal cross section.

Transmutation detectors for fast neutron fluence measurements

Transmutation detectors (TMDs) are based on a similar principle as neutron activation detectors (NADs). In both cases, the neutron fluence is estimated from the number of reactions in the detectors. The main differences between these two detectors are the type of product created by the nuclear reaction and the evaluation of the irradiated detectors. In TMD, the transmuted nuclide is stable, and the number of reactions is gained by analytical methods suitable for measuring low concentrations. In NAD, the nuclear reaction leads to the production of radionuclides and the number of reactions is evaluated from the activity measured by radiometric instruments. While TMDs for thermal neutrons can be easily prepared and evaluated due to their high thermal neutron cross sections for isotopes such as 10B, 115In or 197Au, the requirements for fast neutron TMDs are higher. Cross sections for nuclear reactions suitable for the TMD method with fast neutrons are in the range of 1 to 100 mb for the fission spectrum. This leads to concentrations from 0.01 ppm to 1 ppm for fast neutron fluence of 1E19 cm-2. These low concentrations imply requirements for detector material purity and sensitivity of concentration evaluation equipment. Materials for fast neutron TMDs were proposed, where the relevant parameters, such as energy threshold and minimal detectable fluence are known and convenient. An experimental comparison of some TMD and NAD responses was made in the LVR-15 research reactor using secondary ion mass spectrometry to evaluate the concentration of TMDs.

Gamma rays and neutrons attenuation performance of a developed lead borate glass for radiotherapy room.

The development of radiation therapy necessitated a continuous R&D for radiotherapy rooms' glass windows to reach the highest levels of protection for the staff of the radiotherapy facility. Therefore, in this article, a novel type of lead borate glass depending on parallel augmenting of lead and boron was produced to be used as gamma-rays and fast and thermal neutrons barriers in radiotherapy rooms. Neutrons and gamma rays' attenuation parameters, fast neutrons removal cross section ${\varSigma}_R$, thermal neutron total cross section ${\sigma}_T$, mass attenuation coefficient $\sigma$, linear attenuation coefficient μ, half-value layer, mean free path, effective atomic number Zeff, effective electron density Neff, and buildup factor for energy absorption (energy absorption buildup factor) and exposure (exposure buildup factor) were studied extensively. Three tools, Phy-X/PSD, EpiXS and XCOM computer programs and the standard mixture rules were utilized to estimate the attenuation parameters. The improvement caused by the augmentation of lead and boron in both gamma rays and neutrons attenuation was evident from the obtained results. The glass containing the highest lead and boron concentration PbB5, 40Pb-50B, which is the most efficient attenuator for gamma rays and both thermal and fast neutrons was recommended to be a distinguished choice as a shield in a radiotherapy room.

Neutron shielding analysis for a gadolinium doped nickel alloy

Rare-earth-nickel (RE-Ni) alloy is a kind of appealing neutron shielding material for advanced reactors and spent fuel storage containers. The incorporation of neutron-absorbing additive RE elements results in a RE-Ni alloy with integrated structural and functional features, which can drastically reduce shielding material weight. Gadolinium (Gd), in comparison to other rare-earth elements, has a much larger thermal neutron absorption cross section, necessitating only a low fraction to achieve the desired shielding capability. Hence, gadolinium is doped into a nickel-based alloy to form a gadolinium-nickel (Gd-Ni) alloy. Due to its extremely low solubility in the nickel phase, gadolinium is commonly manifested as heterogeneously spatially scattered Gd-rich phases in existing preparation procedures of alloys rather than homogeneously distributed gadolinium elements. This would result in a strong neutron tunneling effect, limiting the neutron shielding capability of Gd-Ni alloys. In this work, a superfine layered Gd-Ni alloy doped with Gd-rich phases and arranged in dislocations is proposed to provide an adequate dislocation density of Gd-rich phases to suppress the neutron tunneling effect. With the same Gd content, the thermal neutron shielding ability of a layered Gd-Ni alloy is comparable to the case that Gd is assumed to be an ideally homogeneous distribution in the material. The smaller the particle size of the Gd-rich phase, the weaker the neutron tunneling effect, and the lower the thermal neutron transmission ratio. For a 0.5 cm-thick Gd-Ni alloy, the particle size of Gd-rich phase should be kept within 20μm to achieve a thermal neutron transmission ratio of less than 10−5 for natural gadolinium content of 0.6 at.%. This work provides an important guidance for the design and fabrication of the next-generation neutron shielding materials.

Reexamination of a 40Ca(n,α)37Ar cross section measurement from existing literature

Background 37Ar, produced from the neutron activation of 40Ca in sub-surface rock and soil, is important for nuclear explosion monitoring. Most of the cross section measurements done for the 40Ca(n,α) 37 Ar reaction are in the fast neutron region. A thermal cross section measurement was attempted in 1989, with the assumption that the 4-8 MeV neutrons would be completely thermalized with 8-cm of water. Methods The experimental setup was modeled using Monte Carlo N-Particle code to see if the assumptions for the neutron distribution were accurate. A model of a 3.0 MeV deuteron source was used to recreate the neutron source from the experiment. Additional modeling was done using SCALE to compare the predictions of 37Ar yields when using the measured cross section from 1989 compared to current nuclear data models. Results Modeling showed the neutron distribution was closer to 10% thermal and 90% fast as opposed to entirely thermalized. The additional modeling showed how the overestimation of the thermal cross section would affect the predicted yield of 37Ar. Conclusions Based on the modeling results, the assumption that all the 4-8 MeV neutrons are thermalized with 8-cm of water is not accurate. The high fraction of fast neutrons interacting with the Ca will result in an overestimation of the thermal cross section.

Synthesis and optimization of alkaline earth borate glasses doped with Fe2O3: Significance of BaO/MgO on the physical, structural features and radiation shielding performance

In this study, MgO–BaO–B2O3–Fe2O3 glasses were synthesized using the conventional melt and quench method, and the role of BaO and MgO in dictating their structural, physical, and optical properties was investigated. The fast neutrons, electrons, and heavy charged radiation transmission abilities of the glasses were delineated with the aim of evaluating their capacity to act as radiation insulators. The density of the glasses decreased from 3.40 g/cm3 to 2.89 g/cm3 as the MgO content increased. Also, the obtained optical bandgap increased from 1.90 eV to 2.20 eV with the increase of MgO in the MBBFe glasses. The stopping powers of electrons vary from 1.39 to 11.01 MeVcm2/g, 1.41–11.37 MeVcm2/g, 1.43–11.69 MeVcm2/g, 1.44–11.87 MeVcm2/g and 1.46–12.05 MeVcm2/g for glasses with MgO contents of 0 (MBBFe0), 5 (MBBFe1), 10 (MBBFe2), 12.5 (MBBFe3), and 15 (MBBFe4) mol%, respectively. Generally, the increase in the MgO content of the glasses led to increased mass stopping powers of the protons, alpha particles, and carbon ions. The replacement of BaO with MgO compromised the thermal neutron interaction probabilities of the present glassy specimens. The MBBFe-0 glass had the best thermal neutron interaction cross sections. The fast neutron removal cross-section of the glasses was within the range of 0.1037–0.1070 cm−1 with MBBFe-3 having the highest value and MBBFe-4 the least. The increase in the BaO suppresses photon buildup within the glass system. The MBBFe-glasses displayed good physical and optical properties, photon and neutron shielding abilities, which makes them attractive for diverse shielding and optical functions.

An analytical method for beam hardening correction in thermal-neutron radiography

The effect of polychromatic nature of thermal neutrons on neutron radiography was studied through experiments and simulations on borated and non-borated stainless steel with homogeneous composition. The results were compared to theoretical neutron-transmission results obtained for a monochromatic neutron beam.The evolution of total cross sections, neutron-transmission and gray level in neutron radiography image indicate the important effect of beam hardening.For that, an analytical procedure has been established for thermal cross section determination and beam hardening correction of the experimental and simulated data. The corrected data values agree well with those calculated theoretically indicating the effectiveness of the developed correction method.

Hadronic J/ψ regeneration in Pb+Pb collisions

We make use of published yields for D-mesons and J/ψ in Pb+Pb collisions at ALICE and a schematic description of the expansion of the hadron gas to study D-meson collisions during the hadronic break-up phase as a production mechanism for charmonium in relativistic heavy ion collisions at the Large Hadron Collider. Our calculation is based on chemical reaction rates with thermal cross sections for an effective meson interaction among pseudoscalar and vector mesons. We find that due to regeneration, the newly measured J/ψ yields are consistent with anywhere from roughly 25% to 110% of the total yield present at hadronization time. This allows us to bound the fractional abundance of J/ψ immediately after hadronization: 0.28≤dN0J/ψ/dydNeqJ/ψ/dy≤1.13. Our results are robust under the relaxation of the particulars of our schematic description and imply that it will be difficult to distinguish regeneration during hadronization from regeneration by final-state hadronic interactions. Therefore, regeneration must be taken into account when modeling.

Evaluation of the thermal neutron capture cross section and the resonance integral of the 70Zn(n,γ)[formula omitted]Zn reaction

Radiative neutron capture is studied in the 70Zn(n,γ)71m,gZn reaction in order to determine the thermal neutron capture cross sections for the reactions. The resonance integrals are calculated to facilitate corrections for the epithermal neutron component. Thermal cross sections for thermal neutrons and resonance integrals for epithermal neutrons (from cadmium cut-off energy 0.5 eV to 0.1 MeV with filter and without filter) are evaluated.

The reaction rate of radiative n8Li capture in the range from 0.01 to 10 T9

Within the modified potential cluster model (MPCM) with forbidden states, the total cross sections are calculated for capture in the ground and first excited states of the9Li nucleus in then8Li channel in the energy range from 10−5 eV to 5 MeV based onЕ1 andM1 transitions. The experimentally proved resonance atEc.m.= 0.232 MeV in the4P5/2wave andab initio-predicted4P3/2resonance at 1.32 MeV [Phys. Rev. C 103, 035801 (2021)] are considered. The strong impact of the asymptotic constant and channel spectroscopic factors on the total capture cross sections are responsible for the variation in the absolute values within factor two. As a consequence, the thermal cross sections areσtherm=24–46.8 mb. The evaluation ofσthermbased on the extrapolation ofab initiocross sections yields ∼85 mb. The reaction rate is calculated in the temperature range from 0.01 to 10T9. The reported reaction rates are compared at the benchmark point 1T9. The comparison of two datasets [Phys. Rev. C 103, 035801 (2021) and Phys. Rev. C 105, 064608 (2022)] on reaction rates recently calculated in microscopic models in extended temperature intervals shows the essential quantitative and qualitative differences. The comparative joint analysis of the reaction rates of radiative neutron capture on the lithium isotopes6,7,8Li is suggested for the choice of an optimal interval for the asymptotic constants.

241Am Neutron Capture Cross Section Measurement using the NaI(Tl) spectrometer of the ANNRI beamline of J-PARC

ABSTRACT The neutron capture cross-section of 241Am was measured from 10 meV to about 500 keV using the NaI(Tl) spectrometer of the Accurate Neutron-Nucleus Reaction Measurement Instrument (ANNRI) beamline in the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). The total energy detection principle was applied in conjunction with the pulse-height weighting technique to derive the neutron capture yield. The present cross-section results were normalized using a 197Au sample measurement by applying the saturated resonance method. The thermal cross section was measured to be 708 ± 22 b, in agreement with the evaluation in JENDL-5 of 709 b within uncertainties. In the keV region, the evaluated libraries of JENDL-5, ENDF/B-VIII.0 and JEFF-3.3 are in good agreement with the present results over 10 keV but show values lower by 30% to 70% below that energy. Moreover, the results of a resonance shape analysis of the resolved resonance region are also provided in the present paper.

Characterization of local deformation around hydrides in Zircaloy-4 using conventional and high angular resolution electron backscatter diffraction

Zircaloy-4 is used as a fuel cladding material for water reactors, as it has good mechanical properties, corrosion resistance, and a low thermal neutron absorption cross section. However, the mechanical performance of Zircaloy-4 can be reduced during service due to hydrogen uptake and hydride formation. These hydrides are brittle, and often reduce the strength and toughness of materials as well as increase susceptibility to delayed hydride cracking (DHC). In this work, large grain Zircaloy-4 with hydrides was prepared and then cross sectioned using cryo-ion beam polishing, using plasma focused ion beam (pFIB) and broad ion beam (BIB) approaches to enable the preparation of a very high quality flat surface with no preferential etching of either the hydride or zirconium metal (typically metallographic polishing preferentially removes hydrides). Conventional and high angular resolution electron backscatter diffraction (EBSD) analysis were then used to explore morphology, deformation fields, and orientation relationships between the zirconium matrix and hydrides. Four maps were collected for analysis which included hydrides near grain boundaries: (a) where the hydride smoothly decorates across two of the connecting boundaries near a triple junction; (b) where the hydride smoothly decorates the boundary; (c) a mixture of smooth decoration of the interface and protrusion into the grains; (d) fine scale hydride that protrudes into one grain. This work highlights that incompatibility of the hydride within the zirconium matrix is strongly linked to the orientation relationship of the hydride and matrix, and the grain boundary character. These results may enable enhanced understanding of the role of hydrides in fracture as well as stress-induced hydride reorientation and DHC susceptibility.

An Analysis of the Significance of the 14N(n, p) 14C Reaction for Single-Event Upsets Induced by Thermal Neutrons in SRAMs

The thermal neutron threat to the reliability of electronic devices caused by <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B capture is a recognized issue that prompted changes in the manufacturing process of electronic devices with the aim of limiting as much as possible the presence of this isotope nearby device sensitive volumes. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> N can also capture thermal neutrons and release low-energy protons (through the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> N(n,p) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> C reaction) that have high enough linear energy transfer to cause single-event upsets (SEU). Typically, nitrogen is used in thin barrier layers made of TaN or TiN or even as insulator in the form of Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> . Numerical simulations on sensitive volumes calibrated on proton and ion experimental data and with an accurate description of the metallization layer on top of the sensitive region show that the presence of nitrogen in these thin barrier layers can be enough to justify the experimentally observed thermal neutron SEU cross section for a static random access memory sensitive to low-energy protons. Nevertheless, the expected SEU cross section from thermal neutrons is usually a few orders of magnitude lower than that of high-energy particles, therefore, not representing an important threat in atmospheric applications. At the same time, for high-energy accelerators, the contribution to the total soft error rate could become substantial, though easy to handle by margins.