Calculation Of Reaction Rates Research Articles

Reduction of the neutron imaginary potential off the stability line and its possible impact on neutron capture rates

The effect of the isovector imaginary optical potential has been studied experimentally by using the particle-evaporation technique for the $^{11}\mathrm{B}+^{48}\mathrm{Ca}$ reaction with a 21.8 MeV $^{11}\mathrm{B}$ beam. Spectra of neutron, proton, and $\ensuremath{\alpha}$ particles emitted from the neutron-rich compound nucleus $^{59}\mathrm{Mn}$ have been measured and analyzed with traditional optical model potentials with their original parametrizations as well as with adjusted isovector imaginary components. It is shown that the isovector component of the imaginary potential is indispensable in the reproduction of proton and $\ensuremath{\alpha}$-particle yields from this reaction and even needs to be enhanced compared with the suggestions of the original model parametrizations. This can lead to important consequences for astrophysical reaction-rate calculations.

CP asymmetries and higher-order unitarity relations

The main focus of this paper is to introduce a new method to control perturbative calculations of CP asymmetric reaction rates in the Boltzmann equation. CP asymmetries in particle reactions are traditionally calculated in terms of complex couplings, Feynman integrals, and Cutkosky rules. We use an expansion of the $S$-matrix unitarity condition instead, obtaining a general expression for the asymmetries without reference to the imaginary part of the loops. Asymmetry cancelations implied by CPT and unitarity are manifested in a diagrammatic way and easy to track at any order of perturbation theory. We demonstrate the power of this general framework within the right-handed neutrino and top-quark scattering asymmetries in seesaw type-I leptogenesis.

Evidence against the Efimov effect in C12 from spectroscopy and astrophysics

Background: The Efimov effect is a universal phenomenon in physics whereby three-body systems are stabilized via the interaction of an unbound two-body sub-systems. A hypothetical state in $^{12}\mathrm{C}$ at 7.458 MeV excitation energy, comprising of a loose structure of three $\alpha$-particles in mutual two-body resonance, has been suggested in the literature to correspond to an Efimov state in nuclear physics. The existence of such a state has not been demonstrated experimentally. Method: Using the combined data sets from two recent experiments, one with the TexAT TPC to measure $\alpha$-decay and the other with Gammasphere to measure $\gamma$-decay of states in $^{12}\mathrm{C}$ populated by $^{12}\mathrm{N}$ and $^{12}\mathrm{B}$ $\beta$-decay respectively, we achieve high sensitivity to states in close-proximity to the $\alpha$-threshold in $^{12}\mathrm{C}$. Results: No evidence of a state at 7.458 MeV is seen in either data set. Using a likelihood method, the 95\% C.L. $\gamma$-decay branching ratio is determined as a function of the $\beta$-decay feeding strength relative to the Hoyle state. In parallel, calculations of the triple-alpha reaction rate show the inclusion of the Efimov corresponds to a large increase in the reaction rate around $5 \times 10^{7}$ K. Conclusion: From decay spectroscopy - at the 95\% C.L., the Efimov state cannot exist at 7.458 MeV with any $\gamma$-decay branching ratio unless the $\beta$-strength is less than 0.7\% of the Hoyle state. This limit is evaluated for a range of different excitation energies and the results are not favorable for existence of the hypothetical Efimov state in $^{12}\mathrm{C}$. Furthermore, the triple-alpha reaction rate with the inclusion of a state between 7.43 and 7.53 MeV exceeds the rate required for stars to undergo the red giant phase.

Unveiling alloying effects on the catalytic activities of Cu3Pt and Cu3Pd for nonoxidative dehydrogenation and esterification of ethanol

To investigate the alloying effects of the Cu catalyst, we performed extensive density functional theory (DFT) calculations to study the reaction mechanisms of ethanol dimerization to form ethyl acetate (EA) on Cu(111) and CuM(111) with M = Pt or Pd. Specifically, thirty-three reactions along the minimum energy reaction pathways were studied by calculating the energy barrier and reaction energy. To evaluate catalytic performance and determine the rate-determining step (RDS), we calculated reaction rate constants based on the harmonic transition state theory. The DFT results showed that the most widely recognized Colley mechanism for ethanol dimerization to form EA should be revised by including CH3CHO hydrogenation to form CH3CH2O. While the first dehydrogenation was found to be the RDS on Cu(111) and Cu3Pt(111), CH3CHO hydrogenation was identified to be the RDS on Cu3Pd(111). Furthermore, Cu3Pt(111) is about 3 orders of magnitude faster than Cu(111) and Cu3Pd(111) for ethanol nonoxidative dehydrogenation and esterification. This work also provides a benchmark for further examination of ethanol dimerization over other Cu alloys.

Monte-Carlo interpretation of the JANUS Phase 1, Phase 2 and Phase 4 shielding experiments with TRIPOLI-4®

The JANUS Phase 1, Phase 2 and Phase 4 shielding experiments performed in the 90’s in the NESTOR reactor aimed to study deep neutron propagation in mild steel, stainless steel, sodium and boron carbide. Together with the other JANUS phases (up to Phase 9) they represent invaluable experimental database for improving nuclear data for fast reactor applications. Several detectors were used to measure reaction rates at different energy domains. These experiments are interpreted using multiple nuclear data for iron 56 and sodium 23 with the TRIPOLI-4® Monte-Carlo code. Discrepancies up to 30% are obtained between calculated reaction rates and experimental results, which points out that the nuclear data of iron, sodium as well as some other isotopes contained in stainless steel should be improved. The JANUS Phase 4 is inconclusive as it is similar to Phase 2 replacing some steel shields with boron carbide, but the introduced boron carbide zone is too small to give significantly different results.

Systematics of the semimicroscopic proton-nucleus optical potential at low energies relevant for nuclear astrophysics

Astrophysical models studying the origin of the p-nuclei require knowledge of the reaction rates of photodisintegrations and capture reactions. Since experimental data at astrophysically relevant energies are limited, reaction rate calculations rely on Hauser-Feshbach (HF) theory predictions. The HF theory requires nuclear physics input such as masses, level densities, $\gamma$-ray strength functions and proton-nucleus optical potentials (pOMP). The scope of this work is to improve a global semi-microscopic pOMP at energies relevant to the p-process. This is achieved by adjusting the normalization parameters of the OMP to all available proton-capture cross sections measured at low energies. By establishing the systematic behaviour of these parameters, one expects to enhance the predictive power of the pOMP when expanding to mass regions where no data exists. The HF calculations were obtained using TALYS code. The normalization parameters for the real and imaginary central potentials ($\lambda_V$ and $\lambda_W$) were adjusted to fit the proton data in the energy range where the cross-section are independent of the other nuclear inputs. Results show that the $\lambda_V$ parameter has a strong mass dependence that can be described by a second-degree polynomial function for A $\leq$ 100 and an exponential increase for 100 < A < 162. Though variations of the $\lambda_W$ have a smaller effect on the calculations, a global increase by 50$\%$ improves the results for certain nuclei without affecting the rest of the cases. The resulting adjustment functions were obtained by fitting all suitable proton data and can be used with reasonable confidence to generate the global semi-microscopic pOMP for nuclei in the medium to heavy mass region. For better statistics, more low-energy (p,$\gamma$) cross section data are needed for heavier nuclei with mass A $>$ 100.

Kinetics Analysis of Reaction between Molybdenum and Nitrogen Trifluoride

The fluorination behavior of molybdenum (Mo) powder with NF 3 , such as temperature dependence of reactivity, reaction mechanism and kinetics were investigated on a homemade fluoride volatility process (FVP) research device. The in-situ Fourier transform infrared (FTIR) spectroscopy was applied to determine the beginning and the end of reaction. The research demonstrated that near 500 K or lower, the reaction between Mo power and NF 3 occurred, meanwhile, the temperature had an important influence on the average reaction rate and the utilization of NF 3 . When the temperature increased from 500 K to 700 K, the average rate increased from 1.04 × 10 –2 mol/h to 2.40 × 10 –2 mol/h and the utilization of NF 3 increased from 21.2% to 49.0%. The in-situ FTIR and XRD analysis assisted by thermodynamic calculation indicated that Mo power was converted to MoF 6 through an intermediate product MoF 3 : 2NF 3 (g) + 2Mo (s) = 2MoF 3 (s) + N 2 (g), then 2MoF 3 (s) + 2NF 3 (g) = 2MoF 6 (g) + N 2 (g). Based on a mathematical model with unreacted shrinking core, the calculated reaction rate constant increased from 1.77 × 10 –2 min –1 to 3.48 × 10 –2 min –1 in the temperature range of 500–700 K, and the activation energy was 10.13 kJ/mol. Based on the sensitivity of NF 3 ’ reactivity to temperature, the fluorination reaction and the reaction kinetics between Mo power and NF 3 were studied using the in-situ FTIR spectrometer assisted by thermodynamic calculation. The results demonstrated that Mo power was converted to MoF 6 through an intermediate product MoF 3 , and the temperature had a significant effect on the reaction rate and utilization of NF 3 .

Verification and Validation of RAPID Formulations and Algorithms Based on Dosimetry Measurements at the JSI TRIGA Mark-II Reactor

In this paper, detailed verification and experimental validation of the formulations and algorithms of the Multi-stage Response-function Transport (MRT)–based Real-time Analysis for Particle-transport and In-situ Detection (RAPID) code system is presented. In particular, RAPID’s fission matrix formulation for eigenvalue calculations and its detector response function for reaction rate calculations have been examined in this study. As part of a collaboration between Virginia Tech and the Jožef Stefan Institute (JSI), RAPID is used to simulate dosimetry experiments performed at the JSI TRIGA Mark II reactor. In these measurements, wire dosimeters are irradiated at different axial and radial locations in the reactor, and their signature activity is measured. The RAPID calculations require the determination of the fission neutron source distribution and the Au(n,)Au reaction rates in the wires. In addition, the Monte Carlo code Serpent is used for comparison of the RAPID-calculated criticality eigenvalue, three-dimensional fission neutron source distribution. The validation results show excellent agreement of RAPID with both the experiments and the reference Serpent calculation, with an average relative difference of about 3% with respect to the measurements.

Theoretical study on the two novel planar-type all-nitrogen N44− anions: Structures, stability, reaction rate and their stable mechanisms via protonation

Using an unbiased structural search based on a particle-swarm optimization algorithm, two novel N44− anions with planar zigzag and tripod structures were revealed, respectively. Their structures, bonding patterns and charge populations have been theoretically studied. Moreover, H+ cations were selected to saturate the N44− anions to form neutral N4H4 molecules, and the further calculated results showed that the N4H4 compounds have higher kinetic stability than the corresponding N44− anions. Subsequently, the reaction rate calculations also indicated that the N4H4 molecules could remain stable at ambient conditions.

Self-assembly of structured CeCO3OH and its decomposition in H2 for a novel tactic to obtain CeO2- with excellent photocatalytic property

Abstract In this work, various new-observed structured CeCO3OH were synthesized by a self-assembly hydrothermal method, and a novel tactic to produce CeO2-x with excellent photocatalytic activity by decomposing CeCO3OH in H2 was proposed and identified. By controlling the synthetic conditions, almond-like, subglobose shape and hollow-sphere of CeCO3OH, 3D-broom-like of Ce2O3·2CO2·nH2O (n = (1–2)), and sheet-like of Ce2(CO3)3·6H2O were synthesized. The crystal growth and formation of the cerium carbonate compounds were carefully studied using XRD, SEM and TEM. TG, thermodynamic calculation and in-situ XRD were employed to reveal the decomposition behavior of almond-like CeCO3OH in air, Ar and H2. The results show that the decomposition temperatures of CeCO3OH in Ar and H2 are higher than that of in air, and suggest that Ce2O3 has a low thermodynamic stability during the decomposition of CeCO3OH in Ar and H2, and Ce3+ will be mostly oxidized by H2O firstly and then by both of H2O and CO2. The ceria samples obtained by decomposing from CeCO3OH in different atmosphere maintain indistinguishable shape and particle size. The XPS, Raman spectra and ESR results indicate that the one obtained in H2 has the richest surface oxygen vacancies (OVs), narrowest band gap of 3.12 eV, lowest intensity in PL spectra and a significantly enhanced photodegradation ratio of methylene blue. The MB photodegradation ratio after 120 min reaction with the catalysts of CeO2-Air, CeO2-Ar and CeO2-H2 is 43.14%, 54.43% and 73.41%, with a calculated reaction rate constant of 0.00539, 0.00652 and 0.01097 min-1, respectively. The offered novel tactic of decomposing CeCO3OH in H2 is an efficient and facile technique for active CeO2-x production.

Concentration sensing in crowded environments

Signal transduction within crowded cellular compartments is essential for the physiological function of cells. Although the accuracy with which receptors can probe the concentration of ligands has been thoroughly investigated in dilute systems, the effect of macromolecular crowding on the inference of concentration remains unclear. In this work, we develop an algorithm to simulate reversible reactions between reacting Brownian particles. Our algorithm facilitates the calculation of reaction rates and correlation times for ligand-receptor systems in the presence of macromolecular crowding. Using this method, we show that it is possible for crowding to increase the accuracy of estimated ligand concentration based on receptor occupancy. In particular, we find that crowding can enhance the effective association rates between small ligands and receptors to a degree sufficient to overcome the increased chance of rebinding due to caging by crowding molecules. For larger ligands, crowding decreases the accuracy of the receptor’s estimate primarily by decreasing the microscopic association and dissociation rates.

Photocatalytic properties of nanosized zinc ferrite and zinc chromite

A simple one-step synthesis of developed surface zinc ferrite is proposed (S BET = 453.1 m2 g−1). The formation of zinc ferrite, zinc chromite (S BET = 53.6 m2 g−1), and mixed zinc ferrite-chromite (S BET = 37.4 m2 g−1) structures is studied. The resulting materials are analysed using x-ray phase and x-ray fluorescence analysis, IR spectrometry, electron microscopy, TGA and BET method. Single-phase sample formation mechanism is proposed, which includes transition element cation chelate complex formation stage in the presence of citric acid and subsequent thermal decomposition of the complexes formed. The synthesised materials exhibited photocatalytic activity in the decomposition of an organic dye under the action of hydrogen peroxide. The highest catalytic activity is demonstrated by zinc ferrite in acidic medium; the calculated reaction rate constant is 0.010 min−1 for ZnFe2O4, 0.008 min−1 for ZnFeCrO4, 0.007 min−1 for ZnCr2O4. The results can be applied to obtain materials suitable for wastewater treatment processes at industrial enterprises where organic dyes are used in production cycles.

An integrated approach for modeling and identification of perfusion bioreactors via basis flux modes

This paper discusses the challenges associated with the reliable and optimal operation of perfusion bioreactors and presents methods for modeling and identification of perfusion bioreactors as well as the vision for their integration. After presenting a generic model of perfusion bioreactors, the paper shows how to use the concept of basis flux modes to uniquely compute reaction rates. The advantage of this concept with respect to elementary flux nodes and similar concepts in metabolic flux analysis is the reduced number of flux modes that need to be modeled. In addition, a procedure to identify the model and estimate the parameters for each reaction using Monod-type kinetics is presented. It is shown that the rational structure of these kinetic models results in optimization problems that are amenable to tractable computation of globally optimal parameter estimates. The methods are illustrated via examples with simulated or experimental data.

Exploring reactions of amines-model compounds with NH2: In relevance to nitrogen conversion chemistry in biomass

Amine-containing compounds (primary/NH2, secondary/NH and heterocyclic –NH) -are principal nitrogenated species in biomass. Amine radical (NH2) emerge as an important intermediate in the initial stages of biomass combustion and pyrolysis. A detail understanding of the nitrogen conversion chemistry necessitates acquiring accurate reaction rate constants for reactions of NH2 radicals with amine-bearing molecules. With the absence of relevant kinetic parameters, pertinent kinetic model on oxidation of surrogate biomass compounds often utilize values extracted from analogous reactions with OH and CH3 radicals. Herein, we report comprehensive kinetic parameters for H abstraction by NH2 radicals from various C/H sites in seventeen amine model compounds, comprising primary/secondary alkyl and aromatic amines. Fitted activation energies were found to linearly correlate with N–H bond dissociation enthalpies via Evans–Polanyi plots. In primary C2-C4 alkylamines and in diethylamine, abstraction from the α C–H site (gem to the amine group) largely dominates that from the NH2 group. Abstraction from NH and methyl sites in dimethylamine entails comparable importance. A vinylic CH2 group does not alter kinetics of abstraction for unsaturated amines when contrasted with primary amines. Reaction rate constants for H abstraction from heterocyclic-NH structures follow the order carbazole > indole > pyrrole, reflecting corresponding BDHs values for their N–H bonds. Updating kinetic models on combustion of small amines structures, with the newly calculated reaction rate constants, slightly improves their predictive performance toward the yields of NH2/NH3.

Acid hydrolysis-based sugarcane bagasse biorefining for levulinic acid production: Dynamic mechanistic modeling under varying operating conditions

The study on the lignocellulosic material conversion into bio-based platform chemicals, such as levulinic acid (LA), is one of the most promising routes to promote the development of advanced biorefineries. In this work, a dynamic mechanistic model is developed to simulate the LA production from lignocellulosic material. A wide operating range is used to estimate the parameters of the reaction kinetics. Because multi-parameter estimation problem is complex, a genetic algorithm-based optimization procedure is used to determine the optimum parameters values. Measurements are obtained for various reaction times (0 - 45 min) temperatures (150 – 200 °C) and acid concentration of 7.0 % w/v H2SO4. The calculated reaction rates for the state variables, concentrations of LA, glucose, 5-hydroxymethylfurfural and humins are used to construct the dynamic mechanistic model. The prediction of measured state variables was particularly accurate, as determined by the root mean square error (RMSE) and correlation coefficient (R2). Therefore, a satisfactory agreement between experimental LA yield of 57.2 mol% and computed LA yield of 56.4 mol% was achieved (at 200 °C, 7.0 % w/v H2SO4, 45 min). The proposed methodology drives the systematic development of an industrially reliable dynamic mechanistic model for LA production from sugarcane bagasse as a means to increase the LA yields in the biorefinery.

Numerical study on simplified reaction set of ground state species in CO&lt;sub&gt;2&lt;/sub&gt; discharges under Martian atmospheric conditions

The exploration of Mars has attracted increasing interest in these years. The experiments and simulations show that strong electric field triggered by the dust storms in the Martian atmosphere may cause CO&lt;sub&gt;2&lt;/sub&gt; discharge. Studies on this phenomenon will not only help deepen our comprehension on the evolution of Martian surface, but also provide a possibility to realize the &lt;i&gt;in-situ&lt;/i&gt; oxygen generation on Mars based on plasma chemistry. In this paper, a zero-dimensional global model is used to simplify the complicated description of CO&lt;sub&gt;2&lt;/sub&gt; chemical kinetics, therefore a reduced chemistry can be obtained for detailed numerical simulation in the near future. At the beginning of simplification, the graph theoretical analysis is used to pre-treat the original model by exploring the relationship between reacting species. Through the study of connectivity and the topological network, species such as O&lt;sub&gt;2&lt;/sub&gt;, e, and CO prove to be important in the information transmission of the network. While gaining a clearer understanding of the chemistry model, dependence analysis will be used to investigate numerical simulation results. In this way a directed relation diagram can be obtained, where the influence between different species is quantitively explained in terms of numerical solutions. Users could keep different types of species correspondingly according to their own needs, and in this paper, some species with low activeness such as C&lt;sub&gt;2&lt;/sub&gt;O, &lt;inline-formula&gt;&lt;tex-math id="M5"&gt;\begin{document}$ {\mathrm{O}}_{5}^{+} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20210664_M5.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20210664_M5.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, &lt;inline-formula&gt;&lt;tex-math id="M6"&gt;\begin{document}$ {\mathrm{O}}_{4}^{-} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20210664_M6.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20210664_M6.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and species with uncertainties such as &lt;inline-formula&gt;&lt;tex-math id="M7"&gt;\begin{document}$ {\mathrm{C}}_{2}{\mathrm{O}}_{2}^{+} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20210664_M7.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20210664_M7.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, &lt;inline-formula&gt;&lt;tex-math id="M8"&gt;\begin{document}$ {\mathrm{C}\mathrm{O}}_{4}^{+} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20210664_M8.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20210664_M8.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; are removed from the original model. As for the reduction of specific reactions among species, the reaction proportion analysis based on the calculation of reaction rates is used to obtain the contribution of each reaction to the entire process of CO&lt;sub&gt;2&lt;/sub&gt; discharge, through which the important reactions can be selected. Finally, a simplified chemistry model of CO&lt;sub&gt;2&lt;/sub&gt; discharge based on Martian atmospheric conditions, including 16 species and 67 reactions, is established. The numerical simulations show that the trends of species densities based on the simplified chemistry model are highly consistent with those based on the original one, and considerations about the CO&lt;sub&gt;2&lt;/sub&gt; conversion and the energy efficiency are also in line with expectations, which can help deepen the understanding of the essential process of CO&lt;sub&gt;2&lt;/sub&gt; discharge under Martian atmospheric conditions. In addition, the quantitative results of the relationship between reactive species will lay a theoretical foundation for the accurate analysis of various products in Martian dust storm discharges and the realization of Mars &lt;i&gt;in-situ&lt;/i&gt; oxygen generation technology based on plasma chemistry.

A kinetics study on hydrogen abstraction reactions of cyclopentane by hydrogen, methyl, and ethyl radicals.

Hydrogen abstraction reactions of (cyclo)alkanes by radicals play a fundamental role in both combustion and atmospheric chemistry. In this work, we select three common radicals in the pyrolysis of hydrocarbon fuels: hydrogen radical (H[combining dot above]), methyl radical (ĊH3), and ethyl radical (ĊH2CH3) to investigate the kinetics of their hydrogen abstraction reactions with cyclopentane. The rate constants over a broad temperature range of 150-3000 K are calculated by using the multi-structural variational transition state theory in the small-curvature tunneling approximation (MS-CVT/SCT), by which the multi-structural torsional (MS-T) anharmonicity of partition functions, variational effects, and corner-cutting tunneling are all included in dynamics calculations. We stress the particular importance of considering the MS-T anharmonicity in the rate constant calculation for the reaction with the ethyl radical compared to those with hydrogen and methyl radicals. The MS-T anharmonicity significantly accelerates the reaction with the ethyl radical in the whole temperature range, and in particular, it increases the rate constant by a factor of >-9 at 1000 K. We also found that the tunneling effect drastically increases the rate constants at low-temperatures by up to 3-5 orders of magnitudes. The calculated reaction rate constants have an order of .

New Thermonuclear Reaction Rate Equations for Radiative Neutron Capture

The radiative neutron capture reaction rates have been studied at very low energies which are of interest for nuclear astrophysics. The rates for many of these reactions have remained independent of temperature so far. The temperature dependence of the thermonuclear reaction rates have been explored within the statistical model. Apart from the compound nuclear contribution, the pre-equilibrium as well as the direct effects have been taken into account. The corresponding Maxwellian-averaged thermonuclear reaction rates of relevance in astrophysical plasmas at temperatures in the range from 10$^6$ K to 10$^{10}$ K have been calculated. Analytical expression as a function of $T_9$ has been provided for $^6$Li(n,$\gamma$)$^7$Li by fitting the calculated reaction rate.

High resolution measurements with miniature neutron scintillators in the SUR-100 zero power reactor

Three 1-mm3 miniature fiber-coupled scintillators have been used to perform cm-wise resolution measurements of the thermal neutron flux within experimental channels of the SUR-100 facility, a zero power thermal reactor operated by the Institute of Nuclear Technology and Energy Systems at the University of Stuttgart. The detection system is developed at the École Polytechnique Fédérale de Lausanne in collaboration with the Paul Scherrer Institut. Thermal neutrons count rates were measured along the experimental channels I and II, which cross the reactor at the center and tangentially to the core, respectively. The reactor was modelled with the Monte Carlo neutron transport code Serpent-2.1.31. The comparison of experimental and computed reaction rate distributions showed a good agreement within the core region, with discrepancies within 2σ. An unexpected discrepancy, probably caused by a geometric inconsistency in the computational model of the reactor, was observed in the reflector region of the experimental channel I, where a 20% difference (i.e. 8σ) was found between experimental and simulated results. Significant discrepancies, respectively worth 10σ and 15σ, were noticed at distance, in the lead shielding region, for both experimental channels I and II. In addition, reaction rate gradients across the 2.6 cm and 5.4 cm diameters of both channels were measured. A horizontal reaction rate gradient of (9.09 ± 0.20) % was measured within 2.4 cm across the diameter of the experimental channel II, with a difference from computed results of 2%. The absence of a vertical reaction rate gradient inside the experimental channel I was confirmed by measurements.

Calculation of Photons Reaction Rate Resulting at 120 kVp X-ray Tube Voltage and 1 mAs as Function to Digital Imaging and Communications in Medicine Pixel Numbers Using Monte Carlo N-Particle Transport and a Voxel Model of a 29-Year-Old Patient

Calculation of Photons Reaction Rate Resulting at 120 kVp X-ray Tube Voltage and 1 mAs as Function to Digital Imaging and Communications in Medicine Pixel Numbers Using Monte Carlo N-Particle Transport and a Voxel Model of a 29-Year-Old Patient