• Energy Research
• SDSN Greece close

Recent studies have shown straightforward systematic behavior as a function of constant proton and neutron number for neutron-induced fission cross sections of the actinide elements in the incident-neutron energy range 3 to 5 MeV. In this report, the second in a series, fission cross-section values are studied over the MeV incident-neutron energy range, and at 0.0253 eV. Fission-barrier heights and neutron-binding energies are correlated by constant proton and neutron number; however, these systematic behaviors alone do not explain the trends observed in the fission cross-section values.

The 1977 Wapstra and Bos nuclear mass data tables were used to derive tables for thresholds and Q values of nuclear reactions induced by neutrons, protons, deuterons, tritons, /sup 3/He ions, alpha particles, and photons. The tables are displayed on microfiche included with the report.

LBL-9902 NUCLEAR COLLISIONS AT SEVERAL TENS OF MeV PER NUCLEUS* J^rgen Randrup Nuclear Science Division Lawrence Berkeley Laboratory Berkeley, California 94720 PREFACE Nuclear beams with energies of several tens of MeV per nucleon will soon be available at a number of research centers around the world. Such beams offer a tool for probing new aspects of nuclear structure and dynamics. As the energy is raised models and concepts developed for the relatively well-studied lower-energy domain will be pressed to their limits and are likely to grow obsolete as novel phenomena enter the scene. The first part of these notes deals with the theory of ordinary damped collisions; the testing of such theories is one important aspect of the research with higher beam energies. Another is the search for truly novel phenomena and the second part of these noteF contains some more speculative material on that aspect. Notes for lectures given at the Serre-Chevallier Summer School 10-14 September 197s*. France :i is work was supported by the Nuclear Science Division of the U.S. Department of Energy under contract No. W-7405-ENG-48.

Increasing energy demand and environmental awareness have promoted the development of efficient and environment-friendly hydrogen technologies. Water electrolysis (2𝐻2𝑂→2𝐻2+𝑂2) is a promising way to store renewable electricity generated by solar or wind energy into chemical fuel in the form of H2. Water electrolysis is comprised of a hydrogen evolution reaction (HER) on the cathode and an oxygen evolution reaction (OER) on the anode. For both HER and OER, highly catalytic active electrocatalysts are required to lower the overpotentials and to speed up the sluggish kinetics. To date, noble metal catalysts are still the most efficient electrocatalysts for these two reactions, but their high cost and low abundance on Earth limit the scalable application of water electrolysis. Therefore, investigation of alternative catalysts with low cost and high electrocatalytic activity is urgently needed. This thesis focuses on alkaline electrocatalytic HER, as well as related reactions such as OER, and hydrazine oxidation(HzOR)-assistant HER. In terms of material design, the components are introduced to improve conductivity and mass transfer, as well as boost the intrinsic catalytic activity. Moreover, the mechanism was investigated through exploring the link between structure and performance, as well using density functional theory (DFT) calculations. The first two experimental chapters employed a two-dimensional (2D) material, MXene, as support. In Chapter 2, ruthenium single atoms were incorporated onto ultrathin Ti3C2Tx MXene nanosheets to unlock its electrocatalytic activity. The RuSA@Ti3C2Tx presented a 1 A cm−2 HER current density with an over potential of 425.7 mV, outperforming the commercial Pt/C benchmark. Operando Raman test under HER potential showed the different protonation level between RuSA@Ti3C2Tx and Ti3C2Tx, suggesting the different hydrogen absorption energy of the oxygen terminal on the Ti3C2Tx basal plane. Finally, the theoretical calculations confirmed that the RuSA not only facilitates water dissociation, but also modulates the hydrogen After increasing the Ru content and conducting electroreduction, RuTi alloy nanoclusters were constructed on the surface of Ti3C2Tx. Surprisingly, the RuTi@Ti3C2Tx showed better performance in HER, and excellent hydrazine oxidation reaction (HzOR) performance. The overpotential to attain a current density of 10 mA cm−2 for HER was only 14 mV, lower than that of the commercial Pt/C. The HzOR catalytic activity also outperformed most reported work. In addition, the overall hydrazine spitting was conducted in an H-type electrolytic cell, demonstrating superior thermodynamic advantage and good stability. Defect-abundant active carbon (AC-DCD) as support was prepared by the hydrothermal reaction with dicyanamide. Then, the Ru nanoparticles were grown on the surface. Compared to the catalyst with pristine AC as support prepared under same conditions, Ru600@AC-DCD presented a larger electrochemical special area with strain-abundant Ru nanoparticles. Ru600@AC-DCD delivered excellent HER performance in alkaline media, and good catalytic properties in acidic and neutral media. Finally, another novel metal@carbon composite, Ni nanoparticles encapsulated in graphite carbon layers, was synthesized by directly annealing the Ni-imidazole framework precursors at 350 °C in H2/Ar. By tuning the annealing time under H2/Ar flow, Ni nanoparticles with different crystalline phases were synthesized. These Ni@C samples are di-function electrocatalysts for HER and OER in alkaline condition. The mixed-phase catalyst mix2-Ni@C delivered the highest activity to catalyze HER, while the pure hcp phase catalyst hcp-Ni@C showed best OER activity. This work provided a practical method to prepare low-cost difunctional electrocatalysts for overall water electrolysis. In summary, the thesis innovatively contributes to the knowledge in material science and water electrolysis in the aspects of: (i) designing novel supported composite electrocatalysts with high catalytic activity for HER, OER, and HzOR; (ii) monitoring the changing of surface terminal by operando Raman spectroscopy to verify the HER mechanism; (iii) development of metal nanostructures, like RuTi alloy, hcp phase Ni and mixed-phase Ni, via facile methods, and investigation of their unique properties; and (iv) application of large current HER and exploration of the kinetics under different potentials.

A brief history of the discovery of hypernuclei is given and some recent hypernuclei studies are described. Topics include the study of p-shell hypernuclei, /sup 12/C (K/sup -/, ..pi../sup -/) experiment, and hypernuclear gamma rays. 13 references. (WHK)

The development of green and efficient electrocatalysis, which targets the generation and storage of renewable energy by transforming electrical energy to chemical energy, is strongly driven by the challenges we face in increasing energy demand. Consequently, great efforts have been made in exploring efficient electrocatalysts. The conventional trial-and-error approach for electrocatalysts is timeconsuming due to the lack of direct information regarding the atomic-scale properties of electrocatalysts and the underlying elementary reaction mechanisms. To date, the rational molecular design of high-performance electrocatalysts has been extensively used. However, most of these computational studies are still in their infancy and more reliable modelling of electrochemical processes is needed to bridge the gap between experiments and theory. This thesis aims to utilize structural engineering at the atomic scale to develop high-performance electrocatalysts for hydrogen evolution reaction (HER) and chlorine evolution reaction (CER), and model the external factors of the operating environment to provide a better description of electrocatalytic processes. The general background and objectives of this PhD project are presented in Chapter 1. The recent progress in numerical modelling of electrochemical reactions and processes is discussed in Chapter 2. The importance of theoretical identification and understanding of catalytic active sites is highlighted in this chapter. The computational method employed in this project is the density functional theory (DFT), which has been demonstrated to achieve increasing success in the description and understanding of the II complexity of electrocatalysis. Chapter 3 provides a short introduction of the DFT method, including its origin, development, and implementation. Chapters 4-7 present all the research work completed for this project. As metalorganic frameworks (MOFs) are considered a large family of low-dimensional materials, a comprehensive computational study was conducted to investigate the structural properties and electronic properties of one-dimensional (1D) transition metalbased dithiolene MOFs. Their high electrical conductivities offer the potential for electrocatalytic hydrogen evolution, which is examined with the consideration of electrolyte effects in Chapter 4. As the one of main industrial reactions, CER electrolysis is challenging due to the selectivity of Cl2. This can be ascribed to the unavoidable oxygen evolution from the noble metal-based dimensionally stable anodes (DSAs) used in industry. To this end, six TMN4 complex embedded graphene (TMN4@G) single-atom catalysts (SACs) were systematically investigated in Chapter 5. The DFT results predicted that NiN4@G is a promising candidate for efficiently and selectively catalyzing chlorine evolution in acidic solution. Chapter 6 theoretically studied the performance of CER for eight two-dimensional (2D) semiconducting group- VA monolayers with α and β phases. It is suggested that β-arsenene monolayer exhibits high activity and selectivity of gaseous Cl2 generation by virtue of the expected Cl* precursor. In Chapter 7, three low-dimensional Fe/Co/Ni−dithiolene MOFs were purposely selected due to their acid resistance and comprehensively investigated for electrocatalytic CER. The calculated results demonstrate that Ni-based dithiolene MOF can efficiently catalyze the CER via the Cl* pathway. This thesis makes significant contributions to the theoretical understanding of electrochemical processes, materials science, and electrochemical energy conversion and storage through: (i) demonstrating the importance of electronic configurations of metal cations in the electrical conductivities of transition metal-dithiolene MOFs; (ii) proposing a novel strategy for optimizing the electronic structure of materials on the basis of the resonant charge transfer mechanism; (iii) predicting efficient lowdimensional electrocatalysts for Cl2 evolution with the Cl* intermediate rather than the ClO* intermediate; and (iv) investigating the interactions between adsorbates and catalysts to provide a new descriptor for the discovery of high-performance CER electrocatalysts. It is worth noting that the studies on the electrocatalytic properties of low-dimensional materials are still in the early stage. As such, more accurate models and approaches combined with multiscale simulation are needed in future studies, such as the modelling of the electrode-electrolyte interface, dynamic solvent, and electrical double layer.

Nuclear charge distributions for projectile-like and fission-fragment-like reaction products were measured as a function of angle and energy loss at each of the three bombarding energies E/sub L/ = 505, 610, and 710 MeV for the /sup 86/Kr + /sup 139/La reaction. The charge distributions at most angles and energy losses are dominated by a peak centered close to the Z of the projectile. The variances of the Z distributions of this component exhibit a different dependence on energy loss at each of the three bombarding energies. A nucleon exchange model incorporating the effects of the Fermi motion and Pauli Principle is quite successful in accounting for the rate of energy loss per exchange deduced from the charge distriction data. This result suggests that nucleon exchange is the major mechanism for energy dissipation in these collisions. The data are also analyzed in the framework of a phenomenological model, from which diffusion constants are obtained. For large energy losses a second peak appears in the charge distribution with a most probable Z equal to one-half the sum of the projectile and target Z. This component is attributed to fusion-fission. The magnitude of the fusion-fission cross section at 505 and 610 MeVmore » is larger than TDHF predictions. 12 figures, 2 tables.« less

The maximum energy available for dissipation in the thermal-neutron induced fission of /sup 235/U was determined on the basis of the calculated (static) potential energy and the experimental post-scission data. High dissipation is found to be incompatible with experiment. 18 references.

The transduction of light into chemical potential has been actively studies via a variety of mechanisms. Perhaps the most actively pursued approach is via photoredox chemistry. In this project, the authors have used hydrophobic polymer-water interfaces to investigate mechanisms. The paper discusses results on the effect of adsorbing polymers onto latex particles and the use of diblock amphiphilic polymers with interfacial chromophores. It then evaluates the project from the point of view of solar energy conversion.