Atomic Energy Research Articles

Enhancing puncture resistance in critical applications: A combined experimental and numerical approach

The qualification of materials for puncture resistance is essential for applications like pressure vessels and transport containers, particularly for the safe transport of radioactive materials. International regulations, set forth by organizations such as the International Atomic Energy Agency (IAEA) and the Atomic Energy Regulatory Commission (AERB), mandate the design of transport packages capable of withstanding various accident scenarios, including puncture, fire, impact, and immersion, to ensure the safety and integrity of radioactive material transport. This paper establishes a correlation between puncture energy ( E) required to penetrate stainless steel and mild steel plates, both with and without lead backing, as a function of plate thickness ( t) and punch diameter ( d). The simulation of strain and damage caused by punch impact is carried out within the elastoplastic region of structural materials, with a focus on the kinetic strengthening of the material. Abaqus finite element software is employed for numerical simulations, with model parameters derived from experimental stress-strain flow curve data using a curve-fitting technique. Dynamic compression experiments were conducted at the Refueling Technology Division (RTD) in the Bhabha Atomic Research Center (BARC) across a range of strain rates from 600 [Formula: see text] to 1750 [Formula: see text] at room temperature, using a Split Hopkinson Pressure bar. Additionally, drop weight tower (DWT) experiments were performed at RTD in the BARC facility to calibrate numerical simulations. These experiments were carried out on both bare and leaded stainless steel (SS304L) and mild steel (SA516Gr70) plates.

Bending Moiré in Twisted Bilayer Graphene.

Moiré potentials caused by lattice mismatches significantly alter electrons in two-dimensional materials, inspiring the discovery of numerous unique physical properties. While strain modulates the structure and symmetry of the moiré potential, serving as a tuning mechanism for interactions, the impact of out-of-plane deformation, e.g., bending, on the moiré superlattice remains unknown. Here, we performed large-scale molecular dynamics simulations to study the evolution of the moiré superlattice of twisted bilayer graphene under out-of-plane bending deformation. Our findings indicated that curvature-dependent bending caused both global and local lattice structure modifications in the moiré superlattice. We revealed a linear relationship between lattice displacement and bending curvature across varying initial twist angles along with precise regulation of local interlayer rotation. Additionally, the atomic potential energy landscape revealed that the localized atomic stacks underwent a whirlpool-like transformation, becoming a relaxed superlattice. This work opens up new opportunities for tailoring moiré superlattices by using out-of-plane bending engineering.

First-Principles Study on Formation Mechanism of Six-Coordinated Si in Silicophosphate Glass.

Six-coordinated Si ([6]Si) structures are readily formed in silicophosphate glasses with high P2O5 contents. Although experiments and simulations have provided some information on the local configurations around [6]Si, further research on the formation mechanism of [6]Si at the atomic scale is needed. To investigate the formation mechanism of [6]Si, we performed dynamic and static analyses based on first-principles calculations. In first-principles molecular dynamics simulations with models in which all Si atoms are four-coordinated as the initial structure, we observed that the coordination number of Si increased, and the P-Q2 (P-Qn, where n represents the number of bridging oxygen atoms) changed to P-Q3. Atomic energy analysis revealed that the energy decreases with the structural change from P-Q2 to P-Q3 exceeded the energy increase with an increase in the coordination number of Si, stabilizing of the entire system. We conclude that the key factor in the formation of [6]Si is the decrease in energy associated with the change from a nonbridging oxygen in a PO4 tetrahedral structure to bridging oxygen.

Enhancing Quantum Entanglement Through Parametric Control of Atom‐Cavity States

AbstractDicke states form a class of entangled states that has attracted much attention for their applications in various quantum algorithms. They emerge as eigenstates of the Tavis–Cummings (TC) Hamiltonian, a simplification of the Dicke model, which describes an assembly of two‐level atoms trapped in an electromagnetic cavity. In this letter, it is showed that in the regime where the field energy is large with respect to the atomic energy splitting, precise control of the ground state can be implemented. Specifically, pure Dicke states can be selected and produced by appropriate tuning of the parameters. This result may have important applications in quantum engineering and quantum information theory.

The Role of Small Modular Reactors in the Energy Transition to Decarbonization

The global push to reduce greenhouse gas emissions, while meeting the rising demand for electricity, has led to a growing interest in less polluting energy sources. Small Modular Reactors (SMRs) emerge as a key innovation in nuclear power, offering enhanced safety, transportability, and cost-effectiveness. This paper explores the role of SMRs in advancing decarbonization and strengthening energy security, with a focus on their potential deployment in the EU, including with the aim to achieve climate targets and ensure a stable electricity supply. The study evaluates various SMR designs using the International Atomic Energy Agency’s reactor technology assessment toolkit, considering factors such as safety, economic viability, and regulatory challenges. The findings highlight the critical role of informed decision-making in the successful integration of SMRs into national energy grids, addressing both technical and public perception issues. This paper also underscores the importance of SMRs in creating a sustainable and resilient energy future.

Tackling the Activity Trend of Metal-Loaded Metal Nitride Catalysts for NH3 Synthesis by a First-Principles Microkinetic Study.

Ammonia (NH3) is one of the most widely produced chemicals globally, primarily synthesized through the Haber-Bosch process, which requires high temperatures and pressures. Dual-site catalysts can activate N2 and H2 at spatially separated sites, enabling efficient NH3 synthesis under milder conditions. Despite the rapid experimental progress of the dual-site catalysts (e.g., Ni-LaN), the feasibility and design of dual-site catalysts are challenged recently. Herein, the different metal-loaded metal nitride catalyst models are employed, and their activity map for NH3 synthesis is explored by the first-principles microkinetic simulation. The optimum active region of this type of dual-site catalyst is identified in terms of the formation energy (Ev) of nitrogen vacancy (Nvac) on metal nitride and the adsorption energy (EH) of hydrogen atom on metal cluster, with Ev and EH ideally located around ≈1.50 and ≈-0.30eV, respectively. This offers a framework for designing effective metal-loaded metal nitride catalysts for NH3 synthesis. Importantly, this trend aligns with and rationalizes the current experimental observations of metal-loaded metal nitride reported for NH3 synthesis. This theoretical work provides significant insights into NH3 synthesis on dual-site mechanism, and provides a rational direction for designing metal-loaded metal nitride catalysts.

Capacities of metal-doped nanocages for flutamide and cyclophosphamide delivery as anticancer drug.

In this study, the capacities of C46, Ge46, C72, Al36P36, Ni-C46, Ni-Ge46, Cr-C72, and Cr-Al36P36 nanocages to transfer the flutamide and cyclophosphamide as anticancer drugs are investigated. The adsorption parameters and recovery time values for desorption of flutamide and cyclophosphamide drugs from surfaces of nanocages are calculated to propose the acceptable materials for drug delivery. The ΔGadsorption of flutamide and cyclophosphamide on surfaces of studied nanocages are changed from - 2.95 to - 4.12eV. Results indicated that the Ni-Ge46 and Cr-Al36P36 have higher capacities to deliver the flutamide and cyclophosphamide than other metal-doped nanocages. The Ni and Cr adoption increased the recovery time of complexes of flutamide and cyclophosphamide with metal-doped nanocages. The recovery time of flutamide and cyclophosphamide with studied nanocages is changed from 46.96 to 62.92s. Results shown that the recovery time of complexes of flutamide and cyclophosphamide as anticancer drugs with Ni-C46, Ni-Ge46, Cr-C72, and Cr-Al36P36 nanocages in this study is lower than other types of nanostructures including the C, Si, and AlN nanocages and C, Si, and BN nanotubes in previous works. The Ni-Ge46 and Cr-Al36P36 nanocages are proposed as effective nanostructures to deliver the flutamide and cyclophosphamide as anticancer drugs. In this study, structures of C46, Ge46, C72, Al36P36, Ni-C46, Ni-Ge46, Cr-C72, and Cr-Al36P36 nanocages and complexes flutamide and cyclophosphamide with C46, Ge46, C72, Al36P36, Ni-C46, Ni-Ge46, Cr-C72, and Cr-Al36P36 nanocages have been optimized by DFT method, PBE functional, and aug-cc-pVDZ basis set in GAMESS software. The adoption energy of Ni and Cr atoms on C46, Ge46, C72, and Al36P36 and cohesive energy of C46, Ge46, C72, Al36P36, Ni-C46, Ni-Ge46, Cr-C72, and Cr-Al36P36 nanocages are calculated. The thermodynamic parameters, band gap energy, and recovery time of complexes of nanostructures-flutamide and nanostructures-cyclophosphamide are calculated.

Research on the material removal mechanism of vibration-assisted nano-scratch on single-crystal GaN by molecular dynamics.

Single-crystal gallium nitride (GaN) is a semiconductor material known for its hardness and brittleness. This research aims to reveal the differences in the micro-mechanisms of material removal during traditional grinding and ultrasonic vibration-assisted grinding and to provide guidance for the high-efficiency, high-quality planarization processing of single-crystal GaN. To achieve this purpose, molecular dynamics (MD) simulation methods were used to establish a model (30nm × 40nm × 15nm) of single-crystal GaN being scratched by a single abrasive grain with and without ultrasonic vibration assistance. The differences in the surface morphology and subsurface damage formation mechanisms of single-crystal GaN under conditions with and without ultrasonic assistance were compared. The results indicate that, compared to traditional grinding, the periodic ultrasonic vibrations reduce the normal force and result in a more uniform distribution of stress and temperature, thereby mitigating local stress concentration and thermal accumulation effects. Ultrasonic vibration alters the motion of the abrasive grain, expanding the material removal range from 7.384 to 10.315nm, decreasing the number of residual atoms in the machining area, and lowering the chip pileup height at the leading edge of the abrasive grain from 2.063 to 1.528nm. Additionally, the micro-shear deformation induced by ultrasonic vibrations helps to suppress brittle fracturing caused by excessive local stress, thus reducing the thickness of the damaged subsurface. At a scratch depth of 2nm, the total length of dislocation lines in the ultrasonic-assisted scratch is reduced from 185.256 to 33.315 nm compared to traditional scratching. These findings offer new insights into the microscopic mechanisms of material removal in high-efficiency, high-quality grinding processes of single-crystal GaN. This study adopts LAMMPS software for MD simulations to investigate the physical behavior of GaN during the grinding process. The simulation results are then visualized and analyzed using OVITO software to elucidate microstructural changes in the material. During the simulation, the temperature of the Newtonian layer is calculated based on the statistical analysis of atomic velocities under the NVE ensemble. The grinding force applied to the GaN workpiece is determined by differentiating the atomic potential energy. Von Mises stress analysis is adopted to ascertain the stress distribution during the scratching process. Finally, the changes in the crystal structure during scratching are identified and classified using analysis of identified defect structures.

Application of Reactor Technology Assessment for Floating Nuclear Power Plant Site Selection

At ATOMEXPO in 2015, Indonesia expressed its interest in building a Floating Nuclear Power Plant (PLTN). As a technology that is starting to be in demand in various countries, until this paper was written, the only Floating NPP operating commercially in the world is the Akademik Lomonosov from Russia. Indonesia will be included as a newcomer country if it realizes the construction of a Floating NPP. In this regard, the International Atomic Energy Agency (IAEA) published a reactor technology assessment (RTA) guideline. RTA is a method that newcomer countries can use to select a reactor at a predetermined site. This study demonstrated the application of RTA for a different purpose, namely site selection when the reactor has been determined. This is possible because some parameters in RTA are site-specific. This study compared the total score at each site, where the highest total score means the site that needs to be prioritized. The candidate sites used in this study include Gelasa Island, Ujung Lemah Abang (ULA), North Luwu, and Labuhan Badas, and the type of reactor used is KLT-40S, which is used in the Akademik Lomonosov Nuclear Power Plant. The study results found that the site with the highest score was ULA, with a total score of 3.5772, so this site needs to be considered in the construction of the Floating Nuclear Power Plant. Keywords: Nuclear Power Plant (NPP), Floating Nuclear Power Plant, External Hazards, reactor technology assessment (RTA)

Combining real-space and local range separation-The MH24 locally range-separated local hybrid functional.

In this work, the development of a new general-purpose exchange-correlation hybrid functional based on the recent locally range-separated local hybrid approach is presented. In particular, the new functional, denoted as MH24, combines a non-empirical treatment of the admixture of locally range-separated long-range exact exchange with a new real-space separation approach for the real-space exact-exchange admixture governed by the local mixing function (LMF) and a new empirical LYP-based approach for the correlation functional to enable a flexible description of same- and opposite-spin correlation effects. The nine empirical parameters of the MH24 model have been optimized using a state-of-the-art super-self-consistent-field approach, which exploits the sensitivity of specific properties, such as core ionization potentials, electron affinities, and atomization energies, to the exact-exchange admixture in specific regions in real space and the separation of the LMF into a core, valence, and asymptotic part. The optimized MH24 functionals are shown to be able to simultaneously provide good accuracy for valence and core properties as well as for electron affinities and noble gas dimer dissociation curves, while satisfying multiple known exact constraints related to the exact-exchange admixture in hybrid functionals. MH24 is thus a major step toward the development of more sophisticated hybrid functional models.

On the EFT of dyon-monopole catalysis

Monopole-fermion (and dyon-fermion) interactions provide a famous example where scattering from a compact object gives a cross section much larger than the object’s geometrical size. This underlies the phenomenon of monopole catalysis of baryon-number violation because the reaction rate is much larger in the presence of a monopole than in its absence. It is sometimes claimed to violate the otherwise generic requirement that short distance physics decouples from long-distance observables — a property that underpins the general utility of effective field theory (EFT) methods. Decoupling in this context is most simply expressed using point-particle effective field theories (PPEFTs) designed to capture systematically how small but massive objects influence their surroundings when probed only on length scales large compared to their size. These have been tested in precision calculations of how nuclear properties affect atomic energy levels for both ordinary and pionic atoms. We adapt the PPEFT formalism to describe low-energy S-wave dyon-fermion scattering with a view to understanding whether large catalysis cross sections violate decoupling (and show why they do not). We also explore the related but separate issue of the long-distance complications associated with polarizing the fermion vacuum exterior to a dyon and show in some circumstances how PPEFT methods can simplify calculations of low-energy fermion-dyon scattering in their presence. We propose an effective Hamiltonian governing how dyon excitations respond to fermion scattering in terms of a time-dependent vacuum angle and outline open questions remaining in its microscopic derivation.

Protein quality evaluation: FAO perspective.

United Nations agencies have a unique role in achieving the Sustainable Development Goals (SDGs) and aligned global nutrition targets by 2030. According to the latest estimates the world is moving backward in its efforts to end hunger, food insecurity and malnutrition in the presence of a more challenging and uncertain context, including climate change, war conflicts and other challenges. Shifts to plant and novel foods such as insects have been suggested to have good nutritional quality, as well as less environmental impact compared to "traditional" animal source foods. In the context of changing food systems, considering the nutritional quality of foods is essential and accurately assessing protein quality of foods is particularly important, given the large variability in amino acid composition and digestibility between dietary proteins. Indeed, protein quality estimates have the potential to inform policies and programs for actions to improve nutrition throughout the world and have been discussed during past and recent expert consultations. Recently, the Food and Agriculture Organization of the United Nations has been working with the International Atomic Energy Agency and international experts to review and update evidence and related methods on protein quality assessment and to develop a Protein Digestibility Database to aid dialog on the evaluation of protein quality and protein sufficiency in different populations.

Study of atomic diffusion behavior in diffusion welding of NiTi alloy - based on molecular dynamics

NiTi alloy with nearly equiatomic ratios of Ni and Ti, has a unique shape memory effect and biocompatibility. Atomic diffusion is a determinant factor for the diffusion welding of NiTi alloys joining. In general, the atomic diffusion may be mediated by the temperature, time and pressure and so on. Despite the importance of technology, Ni and Ti atoms’ diffusion mechanism, however, still remains un-elucidated. Few works have investigated the movement rules of atoms from the atomic scale. Molecular dynamics simulations of diffusion welding were performed for 200-800ps to investigate the diffusion process of the NiTi alloy composite plate at temperatures of 1000, 1100, 1200, and 1300K. The results show that the holding temperature had the greatest effect on diffusion, with pressure having the least effect. The diffusion coefficients of NiTi, Ni, and Ti were calculated at temperatures of 1000, 1100, 1200, and 1300K, respectively. The diffusion degree of Ni atoms was higher than that of Ti atoms. The diffusion coefficients of Ni and Ti atoms satisfied the Arrhenius equation, and the diffusion activation energy of Ni atoms was lower than that of Ti atoms. Furthermore, this study demonstrates at the atomic scale that the growth of the diffusion layer at high temperatures follows the parabolic growth kinetics law.

Fixed-node errors in real space quantum Monte Carlo at high densities: Closed-shell atomic correlation energies

We consider non-relativistic electron correlation energies of heavy noble gas atoms including the superheavy element Og. The corresponding data enables us to quantify fixed-node errors in real space quantum Monte Carlo methods as a function of the atomic number Z. We confirm that single-reference trial function nodes lead to an overall trend of mild decrease in recovered correlation energy with the increasing Z. This agrees with our previous study that has shown increasing fixed-node biases with the increasing electron density. We also estimate the value of the linear term in the asymptotic expansion of the atomic correlation energy.

Total alpha radioactivity in fertilizers used in the Indian state of West Bengal using CR-39 SSNTDs: Presentation of a comparative view for different types of fertilizers

Use of fertilizers in agriculture soils is a worldwide practice to increase the yield of agricultural products. Fertilizers may contain radioactive elements may be present along with plant’s nutrients in fertilizers. Migrated radioactive elements from the fertilized soils can find their entry into the environment and human body through several ways, which may lead to induce a potential radiological risk to human health. In the present study, total alpha radioactivity concentration in 68 samples of 18 different types of organic and inorganic fertilizers which are commonly used for cultivation in West Bengal and other states of India has been measured using a track-etch technique. Calibration of the CR-39 track detectors used in this measurement has been done using a distributed alpha-radioactive reference source material of IAEA-448 soil, obtained from Reference Materials Group of International Atomic Energy Commission (IAEA). The obtained source mass dependent calibration factors of CR-39 detectors have been used to estimate the alpha radioactivity of the fertilizer samples eliminating the self-absorption of alpha-particles in the sample. The estimated alpha radioactivity values have been found to vary from 29.4 Bq.kg-1 to 114.2 Bq.kg-1, 2.2 Bq.kg-1 to 13.1 Bq.kg-1 and 485.0 Bq.kg-1 to 1125.8 Bq.kg-1 respectively for organic, non-phosphatic and phosphatic fertilizers. The highest alpha radioactivity is exhibited by phosphatic fertilizers and lowest alpha radioactivity is exhibited by non-phosphatic fertilizers. Alpha radioactivity is found to be strongly correlated with phosphate content of the fertilizers. The alpha radioactivity values obtained in our study are consistent with the studies reported worldwide with few exceptions. Considering radiological as well as other aspects, farmers should be encouraged to use non-phosphatic fertilizers in combination and try to avoid phosphatic fertilizers as far as practicable.

Anthropogenic actinides in seawater and biota from the west coast of Sweden

The assessment of the origin of the anthropogenic contamination in marine regions impacted by other sources than global fallout is a challenge. This is the case of the west coast of Sweden, influenced by the liquid effluents released by the European Nuclear Reprocessing Plants through North Sea currents and by Baltic Sea local and regional sources, among others. This work focused on the study of anthropogenic actinides (236U, 237Np and 239,240Pu) in seawater and biota from a region close to Gothenburg where radioactive wastes with an unknown composition were dumped in 1964. To this aim, a radiochemical procedure for the sequential extraction of U, Np and Pu from biota samples and the subsequent analysis of 236U, 237Np, 239Pu and 240Pu by Accelerator Mass Spectrometry was developed. The method was validated through the study of two reference materials provided by the International Atomic Energy Agency (IAEA): IAEA-446 (Baltic Sea seaweed) and IAEA-437 (Mediterranean Sea mussels). The 233U/236U atom ratio was also studied in the seawater samples. The obtained results indicate that the North Sea currents and global fallout are the major sources for 236U, 237Np and 239,240Pu to the studied area, without clear evidence of other local sources. Complementary, information on the Concentrations Factors (CF) in biota was obtained, for which the available information is very scarce. For seaweed, CF values of (4.07 ± 0.90)·103, 61 ± 22 and 76 ± 16 have been obtained for Pu, Np and U, respectively. Lower CF values of (3.37 ± 0.78)·102, 34 ± 10 and 15.9 ± 3.4 for Pu, Np and U, respectively, have been obtained for mussels.

Preparation and Adsorption Properties of a Three-Dimensional Superhydrophilic Mercury-Ion-Imprinted Polymer with Dual Recognition Site Based on MoS2/SBA-15.

Water pollution resulting from Hg(II) ions has garnered significant global concern for public health. The flexibility and simplicity of design, cost savings, and ease of operation with adaptive designs provide adsorption with a considerable advantage over other processes. However, MoS2 is hydrophobic in nature, which limits its efficiency in the removal of Hg(II) ions from water. Therefore, the incorporation of hydrophilic SBA-15 as supporting material, combined with a nanoflower-like layered MoS2 and its highly reactive exposed edges, produces hydrophilic properties that effectively eliminate Hg(II) from water . A mercury-ion-imprinted polymer (Hg(II)-IIP) was synthesized on the MoS2/SBA-15 surface using N-allylthiourea (ATU) as a functional monomer to enhance material selectivity and create dual recognition sites. Characterization investigation using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and water contact angle showed the successful synthesis of Hg(II)-IIP, excellent hydrophilicity, and close interaction between MoS2 and SBA-15. The maximum adsorption capacity of Hg(II)-IIP for Hg(II) under optimized adsorption conditions was 567.78 mg·g-1 in 90 min, which was 6 times greater than that of the IIP solely based only on SBA-15, and followed by pseudo-second-order and aligned more closely fits with the Langmuir adsorption isotherm. Furthermore, the adsorption capacity of the synthesized Hg(II)-IIP was greater than that of three other common monomers IIP. Hg(II)-IIP possesses a strong ability to regenerate, while also showing better selectivity for Hg(II) in the presence of other interfering ions, indicating its robust anti-interference capability in the multivariate mixed solution. The analysis of the actual sample indicated that Hg(II)-IIP attained recoveries between 97.92 and 100.28% in water samples. Theoretical calculations using density functional theory (DFT) and frontier molecular orbital (FMO) indicated that the binding energy of the sulfur atom forming a tetra-ligand with Hg(II) on ATU was 0.6511 eV greater than that of a diligand. The energy gap was determined to be 0.1550 eV, supporting the preference for S-Hg tetra-ligand adsorption.

Study of atomic sputtering and transport dynamics by Monte Carlo simulation

Magnetron sputtering vacuum coating technology is widely used in Accident Tolerant Fuel (ATF) cladding materials. The growth of thin films is a crucial step in the magnetron sputtering process, closely linked to the energy and angular distribution of atoms sputtered from the target to the substrate. However, experimental investigations of atomic sputtering are challenging due to the difficulty of accurately detecting electron distributions, incident ion distributions, and quantities, especially collisions between sputtered and vacuum chamber gas atoms. In this study, the SRIM/SIMTRA programs based on the Monte Carlo method have been carried out to predict the energy and angular distributions of sputtered atoms from the target surface and to calculate the energy, angle, and number distributions of supering atoms arriving on the substrate after traversing the vacuum chamber. The results of SRIM indicate the sputtered atom distribution in the low-energy region, with the scattering angles exhibiting a ‘heart-shaped’ profile. Additionally, SIMTRA simulation results show that increasing the target-substrate distance (TSD) and vacuum chamber gas pressure leads to significant attenuation of the energy of atoms arriving on the substrate and a tendency for larger incidence angles. These simulation outcomes provide crucial theoretical guidance for optimizing magnetron sputtering coating performance for ATF cladding.

Study on potential burnable poison materials for a small modular block-type HTGR design using MgO-BeO as a composite-based moderators

Preliminary analysis of MgO-BeO composite material used as a moderator in a 50 MWt block-type high-temperature gas-cooled reactor (HTGR) was performed in our previous study. The target burnup of 80 GWd/t was achieved with a uniform fuel composition of 17 wt% 235U enrichment and 6 kg of heavy metal per fuel block. However, this resulted in high excess reactivity and a peak in axial power distribution at the core center. Therefore, this study aims to reduce excess reactivity by incorporating burnable poison (BP) material and optimize the axial power profile by introducing a nonuniform fuel composition in the core. Neutronic calculations were performed using the Monte Carlo MVP3.0 code developed by the Japan Atomic Energy Agency (JAEA). In this study, three fuel enrichments of 235U, ranging from 15 wt% to 20 wt%, were distributed across the core while maintaining a constant fuel packing fraction of 45 %. The results showed that the higher power density distribution shifted from the core’s center to its upper part, leading to lower power density in the bottom region than the top. In addition, excess reactivity was reduced by inserting BP rods. Several parametric calculations were performed to achieve minimal excess reactivity without compromising the burnup target. The results showed that the BP rod with a radius of 0.7 cm and 12 wt% of Gd2O3 can reduce the excess reactivity from 25.5 %Δk/k to 13.47 % Δk/k.

Factors influencing quantum evaporation of helium from polar semiconductors from first principles

While there is much indirect evidence for the existence of dark matter (DM), to date it has evaded detection. Current efforts focus on DM masses over ∼GeV—to push the sensitivity of DM searches to lower masses, new DM targets and detection schemes are needed. In this work, we focus on the latter—a novel detection scheme recently proposed to detect 10–100 meV phonons in polar target materials. Previous work showed that well-motivated models of DM can interact with polar semiconductors to produce an athermal population of phonons. This new sensing scheme proposes that these phonons then facilitate quantum evaporation of He3 from a van der Waals film deposited on the target material. However, a fundamental understanding of the underlying process is still unclear, with several uncertainties related to the precise rate of evaporation and how it can be controlled. In this work, we use density functional theory calculations to compare the adsorption energies of helium atoms on a polar target material, sodium iodide, to understand the underlying evaporation physics. We explore the role of surface termination, monolayer coverage, and elemental species on the rate of He evaporation from the target material. Using this, we discuss the optimal target features for He-evaporation experiments and their range of tunability through chemical and physical modifications such as applied field and surface termination. Published by the American Physical Society 2024