Hasil untuk "Nuclear and particle physics. Atomic energy. Radioactivity"

NI Weixuan, JIA Lixia, DOU Yankun, HE Xinfu, CAO Jinli, WANG Dongjie, YANG Wen

Molybdenum (Mo) alloys are widely employed in high-temperature environments, such as advanced nuclear systems, due to their excellent properties, including high melting point and thermal conductivity. However, Mo alloys suffer from poor ductility at room and intermediate temperatures, which can be improved by adding rhenium (Re) or dispersing second-phase particles. These particles refine the grain size by promoting nucleation and inhibiting grain growth, improving strength while reducing the concentration of harmful solutes. Nevertheless, creep behavior is a critical performance aspect for Mo-Re alloys during service, as it can limit their high-temperature applications. Creep refers to the time-dependent plastic deformation that occurs at high-temperatures under stress levels below the yield strength of a material. In polycrystalline Mo alloys, grain boundary sliding exacerbates creep at elevated temperatures, restricting their use. Previous studies on Mo creep behavior have indicated that subgrain formation and grain growth occur during high-temperature service, and nanocrystalline materials exhibit distinct creep mechanisms compared to polycrystalline counterparts. Recent findings suggest that nanocrystalline materials can experience significant creep even at lower temperatures, indicating the importance of investigating the effects of high grain boundary density on the creep behavior of Mo alloys. Given that experimental creep tests require long durations, molecular dynamics (MD) simulation offers an efficient alternative for studying atomic-scale processes at grain boundaries. In this study, MD simulation was employed to investigate the tensile creep behavior of nanocrystalline Mo with varying grain sizes under different temperature and stress conditions. The Voronoi method was used to generate nanocrystalline Mo structures with random grain orientations, and tensile creep simulations were conducted using the LAMMPS software. The results reveal that increasing temperature and applied stress accelerates the creep process, with smaller grain sizes exhibiting more pronounced creep behavior. Atomic-level visualization shows that dislocation density and grain structures remain largely unchanged, while local atomic environments change due to vacancy diffusion along grain boundaries. These changes are responsible for the observed deformation mechanisms, particularly Coble creep, which dominates under the simulated conditions. This study provides valuable insights into the mechanisms of creep in nanocrystalline Mo at 800-1 400 K, which is critical for its potential application in nuclear industry designs. The findings highlight the importance of understanding grain boundary diffusion and its role in controlling the overall creep behavior in nanocrystalline materials.

Benjamin Berczi, Magdalena Eriksson, Thanasis Giannakopoulos et al.

Abstract We report on work using a newly developed code, SpheriCo.jl, that computes the gravitational collapse of a spherical scalar field, where the scalar can be either a classical field, or a quantum field operator. By utilising summation-by-parts methods for the numerical derivatives we are able to simulate the collapse longer than was possible previously due to enhanced numerical stability. We present a suite of tests for the code that tests its accuracy and stability, both for the classical and quantum fields. We are able to observe critical behavior of gravitational collapse for the classical setup, in agreement with expected results. The code is also used to compute two-point correlation functions, with results that hint at a non-trivial correlation across the horizon of Hawking quanta.

Theodore Jacobson, Tin Sulejmanpasic

Abstract We discuss the canonical quantization of U(1) k Chern-Simons theory on a spatial lattice. In addition to the usual local Gauss law constraints, the physical Hilbert space is defined by 1-form gauge constraints implementing the compactness of the U(1) gauge group, and (depending on the details of the spatial lattice) non-local constraints which project out unframed Wilson loops. Though the ingredients of the lattice model are bosonic, the physical Hilbert space is finite-dimensional, with exactly k ground states on a spatial torus. We quantize both the bosonic (even level) and fermionic (odd level) theories, describing in detail how the latter depends on a choice of spin structure.

Eberhard Altstadt, Frank Bergner, Jann-Erik Brandenburg et al.

Neutron irradiation causes embrittlement of reactor pressure vessel (RPV) steels. Post-irradiation annealing is capable of partly or fully restoring the unembrittled condition. While annealing at high temperatures (e.g., 475°C) was successfully applied to extend the lifetime of operating VVER-440 reactors, the benefit of annealing at lower temperatures (e.g., 343°C–the maximum to which the primary cooling water can be heated) is a matter of debate. In this study, neutron-irradiated VVER-440 RPV base metal and weld were exposed to isothermal annealing at 343°C up to 2,000 h. Given the limited amount of material, the degree of recovery was estimated in terms of Vickers hardness, the ductile-brittle transition temperature derived from small punch tests, and the master curve reference temperature derived from fracture mechanics tests of mini samples. For the base metal, small-angle neutron scattering was applied to underpin the findings at the nm-scale. We have found significant partial recovery in both materials after annealing for 300 h or longer. The variations of the degree of recovery are critically discussed and put into the context of wet annealing.

A. Alves, G. Gil da Silveira, V. P. Gonçalves et al.

Abstract We derive the discovery potential of a leptophilic $$Z^\prime $$ Z ′ , and a $$Z^\prime $$ Z ′ rising from a $$SU(3)_C \times SU(3)_L \times U(1)_N$$ S U ( 3 ) C × S U ( 3 ) L × U ( 1 ) N symmetry at the Compact Linear Collider (CLIC), which is planned to host $$e^+e^-$$ e + e - collisions with 3 TeV center-of-mass energy. We perform an optimized selection cut strategy on the transverse momentum, pseudorapidity, and invariant mass of the dileptons in order to enhance the collider sensitivity. We find that CLIC can potentially reach a $$5\sigma $$ 5 σ signal of a $$1-5$$ 1 - 5  TeV leptophilic $$Z^\prime $$ Z ′ with less than 1 fb $$^{-1}$$ - 1 of integrated luminosity in the most favorable cases. As for the $$Z^\prime $$ Z ′ belonging to a 3-3-1 symmetry, CLIC will offer a complementary probe with the potential to impose $$M_{Z^\prime } > 3$$ M Z ′ > 3  TeV with $${\mathcal {L}}=2$$ L = 2 fb $$^{-1}$$ - 1 .

Taro Konomi, Kensei Umemori, Hiroshi Sakai et al.

A 10-kW-class high-power extreme ultraviolet light source is required in mass microfabrication technologies, and a free-electron laser based on an energy recovery linac (ERL) is an attractive candidate. The design beam current is 9.75 mA, and the beam energy is 800 MeV. The cavity design is required to achieve a target gradient of 12.5  MV/m with a high yield and efficient suppression of radiofrequency power losses through higher-order modes (HOMs). The HOMs generated in the cavity pass through the end cells and are damped by the beam-tube dampers. The cavity was designed mainly to reduce the heat generated by the monopole modes. Further, the transverse shunt impedance of dipole modes must be smaller than the specification related to the beam breakup effect. Considering the cavity design, the end cell was optimized by selecting the appropriate frequency obtained using the tuning curve method. The shape of the HOM damper was designed using the complex permittivity data obtained from the S-parameter method with sample pieces. This cavity design was confirmed to have a sufficient margin of accelerating gradient and adequately damped HOMs for the 10-mA-class ERL operation.

The Belle collaboration, V. Zhukova, R. Mizuk et al.

Abstract We report the first measurement of the inclusive e + e − → b b ¯ $$ b\overline{b} $$ → D s ± $$ {D}_s^{\pm } $$ X and e + e − → b b ¯ $$ b\overline{b} $$ → D 0 / D ¯ 0 $$ {\overline{D}}^0 $$ X cross sections in the energy range from 10.63 to 11.02 GeV. Based on these results, we determine σ(e + e − → B s 0 B ¯ s 0 $$ {B}_s^0{\overline{B}}_s^0 $$ X) and σ(e + e − → B B ¯ $$ B\overline{B} $$ X) in the same energy range. We measure the fraction of B s 0 $$ {B}_s^0 $$ events at Υ(10860) to be f s = ( 22.0 − 2.1 + 2.0 $$ {22.0}_{-2.1}^{+2.0} $$ )%. We determine also the ratio of the B s 0 $$ {B}_s^0 $$ inclusive branching fractions B $$ \mathcal{B} $$ ( B s 0 $$ {B}_s^0 $$ → D 0 / D ¯ 0 $$ {\overline{D}}^0 $$ X)/ B $$ \mathcal{B} $$ ( B s 0 $$ {B}_s^0 $$ → D s ± $$ {D}_s^{\pm } $$ X) = 0.416 ± 0.018 ± 0.092. The results are obtained using the data collected with the Belle detector at the KEKB asymmetric-energy e + e − collider.

Zhe Chen, Haijun Ren

The geodesic acoustic mode (GAM) is investigated with gyro-kinetic equations in Miller local equilibrium model for shaped tokamak plasmas with an arbitrary elongation κ and a finite triangularity δ . In particular, the effects of triangularity on GAM frequency and damping rate are analyzed both analytically and numerically. The asymptotic analytical and exact numerical results both show that the frequency almost linearly increases with the triangularity but increases relatively more slowly for a negative δ , which agree well with the TCV observation on the trend. The analytical results clearly claim that the triangularity effect strength is dependent on the inverse aspect ratio $\epsilon$ and Shafranov shift gradient $\Delta^{^{\prime}}$ , while the numerical results indicate that the safety factor q also has a significant impact on the triangularity effects. In addition, the damping rate increases rapidly with triangularity when q is not too large and then saturates when δ is above about 0.3.

Kara Farnsworth, Michael L. Graesser, Gabriel Herczeg

Abstract The Newman-Penrose map, which is closely related to the classical double copy, associates certain exact solutions of Einstein’s equations with self-dual solutions of the vacuum Maxwell equations. Here we initiate an extension of the Newman-Penrose map to a broader class of spacetimes. As an example, we apply principles from the Newman-Penrose map to associate a self-dual gauge field to the Kerr-Taub-NUT-(A)dS spacetime and we show that the result agrees with previously studied examples of classical double copies. The corresponding field strength exhibits a discrete electric-magnetic duality that is distinct from its (Hodge star) self-dual property.

Zehua Tian, Jiliang Jing

Abstract It is found that the Unruh effect can not only arise out of the entanglement between two sets of modes spanning the left and right Rindler wedges, but also between modes spanning the future and past light cones. Furthermore, an inertial Unruh–DeWitt detector along a spacetime trajectory in one of these cones may exhibit the same thermal response to the vacuum as that of an accelerated detector confined in the Rindler wedge. This feature thus could be an alternative candidate to verify the “Unruh effect”, termed as the timelike Unruh effect correspondingly. In this paper we propose to detect the timelike Unruh effect by using an impurity immersed in a Bose–Einstein condensate (BEC). The impurity acts as the detector which interacts with the density fluctuations in the condensate, working as an effective quantum field. Following the paradigm of the emerging field of quantum thermometry, we combine quantum parameter estimation theory with the theory of open quantum systems to realize a nondemolition Unruh temperature measurement in the nanokelvin ( $$\textrm{nK}$$ nK ) regime. Our results demonstrate that the timelike Unruh effect can be probed using a stationary two-level impurity with time-dependent energy gap immersed in a BEC within current technologies.

J. Balibrea, J. Benito, B. Fernandez et al.

Masashi Aiko, Shinya Kanemura, Mariko Kikuchi et al.

We discuss a possibility that the parameter space of the two Higgs doublet model is significantly narrowed down by considering the synergy between direct searches for additional Higgs bosons at the LHC and its luminosity upgraded operation and precision measurements of the Higgs boson properties at future electron-positron colliders such as the International Linear Collider. We show that, in the case where the coupling constants of the discovered Higgs boson are slightly different from the predicted values in the standard model, most of the parameter space is explored by the direct searches of extra Higgs bosons, in particular for the decays of the extra Higgs bosons into the discovered Higgs boson, and also by the theoretical arguments such as perturbative unitarity and vacuum stability. This can be done because there appears an upper limit on the mass of the extra Higgs bosons as long as the deviation exists in the Higgs boson coupling. We also show that in the alignment limit where all the Higgs boson couplings take the standard model like values most of the parameter space cannot be excluded because most of the Higgs to Higgs decays are suppressed and also there is no upper limit on the masses from the theoretical arguments.

Shai M. Chester, Walter Landry, Junyu Liu et al.

Abstract We develop new tools for isolating CFTs using the numerical bootstrap. A “cutting surface” algorithm for scanning OPE coefficients makes it possible to find islands in high-dimensional spaces. Together with recent progress in large-scale semidefinite programming, this enables bootstrap studies of much larger systems of correlation functions than was previously practical. We apply these methods to correlation functions of charge-0, 1, and 2 scalars in the 3d O(2) model, computing new precise values for scaling dimensions and OPE coefficients in this theory. Our new determinations of scaling dimensions are consistent with and improve upon existing Monte Carlo simulations, sharpening the existing decades-old 8σ discrepancy between theory and experiment.

Koushik Ganesan, Andrew Lucas

Abstract We revisit the theory of strongly correlated quantum matter perturbed by Harris-marginal random-field disorder, using the simplest holographic model. We argue that for weak disorder, the ground state of the theory is not Lifshitz invariant with a non-trivial disorder-dependent dynamical exponent, as previously found. Instead, below a non-perturbatively small energy scale, we predict infrared physics becomes independent of the disorder strength.

Karine Beaugelin-Seiller, Brenda J. Howard, Jacqueline Garnier-Laplace

Denise Alves Fungaro, Denise Alves Fungaro, Paulo Sergio Silva et al.

Neutron activation analysis and gamma-ray spectrometry was used to determine 238U, 226Ra, 228Ra, 210Pb, 232Th and 40K contents in feed pulverized coal, bottom ash, fly ash from cyclone and baghouse filters, zeolites synthesized from the ashes and two different soil samples. All the samples used in the study was collected at Figueira thermoelectric power plant, located in the city of Figueira, Paraná State, which coal presents a significant amount of uranium concentration. The natural radionuclide concentrations in pulverized coal were 4216 Bq kg–1 for 238U, 180 Bq kg–1 for 226Ra, 27 Bq kg–1 for 228Ra, 28 Bq kg–1 for 232Th and 192 Bq kg–1 for 40K. The ashes fraction presented concentrations ranging from 683.5 to 1479 Bq kg–1 for 238U, from 484 to 1086 Bq kg–1 for 226Ra, from 291 to 1891 Bq kg–1 for 210Pb, from 67 to 111 Bq kg–1for 228Ra, from 80 to 87 Bq kg–1 for 232Th and from 489 to 718 Bq kg–1 for 40K. Similar ranges were observed for zeolites. The activity concentration of 238U was higher than worldwide average concentration for all samples. The concentration of the uranium series found in the ashes were lower than the values observed in similar studies carried out 10 years ago and under the limit adopted by the Brazilian guideline (CNEN-NN-4.01). Nevertheless, the concentrations of this specific area are higher than others coal mines and thermoelectric power plants in and out of Brazil, so it is advisable to evaluate the environmental impact of the installation.