Equations of state and phase diagrams of hydrogen isotopes

A new form of the semiempirical equation of state proposed for the liquid phase of hydrogen isotopes is based on the assumption that its structure is formed by cells some of which contain hydrogen molecules and others contain hydrogen atoms. The values of parameters in the equations of state of the solid (molecular and atomic) phases as well as of the liquid phase of hydrogen isotopes (protium and deuterium) are determined. Phase diagrams, shock adiabats, isentropes, isotherms, and the electrical conductivity of compressed hydrogen are calculated. Comparison of the results of calculations with available experimental data in a wide pressure range demonstrates satisfactory coincidence.     

Commercial cyclotrons. Part I: Commercial cyclotrons in the energy range 10–30 MeV for isotope production

A survey of commercial cyclotrons for production of medical and industrial isotopes is presented. Compact isochronous cyclotrons which accelerate negative hydrogen ions in the energy range 10–30 MeV have been widely used over the last 25 years for production of medical isotopes and other applications. Different cyclotron models for the energy range 10–12 MeV with moderate beam intensity are used for production of ¹¹C, ¹³N, ¹⁵O, and ¹⁸F isotopes widely applied in positron emission tomography. Commercial cyclotrons with high beam intensity are available on the market for production of most medical and industrial isotopes. In this work, the physical and technical parameters of different models are compared. Possibilities of improving performance and increasing intensity of H^? beams up to 2–3 mA are discussed.     

Structural transitions in hydrogen and deuterium at ultrahigh pressures

Abstract

Raman measurements indicate that normal hydrogen and deuterium compressed in a diamond-anvil cell at 77 K undergo phase transformations at 145 (±l5) GPa and 190 (±l20) GPa, respectively. The new observations reported for deuterium indicate that the transition in both isotopes is a structural change not associated with a simple rotational ordering mechanism. The possibility of a structural transition driven by band-gap closure is discussed.     

The effect of diatom-diatom collisions on depolarized light scattering linewidths : I. General theory

With the use of an appropriately generalized Waldmann-Snider collision (super-) operator, a unified kinetic theory treatment of depolarized light scattering (both depolarized Rayleigh and rotational Raman) and their related linewidths is presented for gases of rigid rotor molecules. Explicit expressions are given, both exactly and within a distorted wave Born approximation, for the various state-to-state (i.e. rotational quantum number dependent) collision processes which can contribute to any observed linewidths due to diatom-diatom collisions. The results of this paper are employed in the calculation of the depolarized linewidths for the hydrogen isotopes in the following article.     

声波作用下液滴碰并沉降及其氢氧同位素特征

液滴沉降过程中会与环境水汽发生物质交换.论文通过小尺度室内实验,研究了低频声波作用下液滴碰并沉降及其与气室环境水汽氢氧同位素交换特征.研究结果证实液滴沉降过程中存在同位素交换,该过程受声波显著影响.声波作用后液滴粒径增大,液滴沉降后汇集水中重同位素出现富集.液滴与环境水汽氢氧同位素交换强度与液滴初始粒径呈正相关,声波对...     

D2/H2 quantum sieving in microporous carbons: a theoretical study on the effects of pore size and pressure

The adsorption of hydrogen and deuterium in slit-shaped carbon pores is studied by grand canonical Monte Carlo simulations. All interactions are assumed to be of Lennard–Jones type, while the Feynman–Hibbs expression is used to account for quantum effects. The interaction energy of both isotopes inside the slit pore space is discussed thoroughly. Furthermore, pure component adsorption isotherms of both isotopes were simulated at 77?K for pressures up to 20?bar in slit pores having widths of up to 2.0?nm. According to our simulations, in equilibrium, slit pores reveal slight deuterium selectivity over hydrogen, and this quantum-based selectivity depends both on pressure and pore size.     

Spin-flip cross sections in muonic hydrogen scattering on hydrogen molecules

The results of calculations of the total cross sections of spin-flip processes in low energy muonic hydrogen scattering on hydrogen molecules are presented. These calculations are based on the respective set of cross sections for muonic hydrogen scattering on hydrogen nuclei, obtained within the framework of the multichannel adiabatic method. All combinations of the three hydrogen isotopes are considered. Molecular binding effects are described in terms of the Fermi pseudopotential method. Electron screening effects are calculated in the distorted wave Born approximation. Rotational and vibrational transitions of the molecules, due to collisions with muonic hydrogen atoms, are taken into account. The molecular and electron screening corrections do not exceed a few tens per cent for lowest collision energies.     

Isentropic Compression of Substances Using Ultra‐High Magnetic Field: Zero Isotherms of Protium and Deuterium in Pressure Range up to ∼5 Mbar

Experiments on isentropic compression of a substance using a high magnetic field pressure are described. Their goal is building of a zero isotherm in a multi‐megabar pressures range. A method of the pressure and density determination of the compressed substance based on radiographic data obtained in the experiment is presented. The results of the experiments with solid (in initial state) protium and deuterium are presented. The densities that correspond to more than seventeen‐fold compression are reached. Obtained experimental points are compared with extrapolation of a curve that is built in the experiments using anvil cells and with the results of several ab‐initio calculations (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrogen and deuterium in shock wave experiments,ab initio simulations and chemical picture modeling

We present equation of state data of shock compressed hydrogen and deuterium. These have been calculated in the physical picture by using ab initio molecular dynamics simulations based on finite temperature density functional theory as well as in the chemical picture via the Saha-D model. The results are compared in detail with data of shock wave experiments obtained for condensed and gaseous precompressed hydrogen and deuterium targets in a wide range of shock compressions from low pressures up to megabars.     

Spectroscopy of superheavy hydrogen isotopes in stopped-pion absorption by nuclei

The structure of levels of superheavy hydrogen isotopes ^4–6H is analyzed on the basis of a record statistics of experimental data on the absorption of negatively charged pions by light nuclei. Qualitatively new experimental data are obtained for the spectroscopy of the superheavy hydrogen isotopes ⁵H and ⁶H. Peaks due to four resonance states of ⁵H are observed in the missing-mass spectra for the reaction channels ⁹Be(π ^?, pt)X and ⁹Be(π^?, dd)X. A structure that is associated with four resonance states of ⁶H is observed in the missing-mass spectra for the reaction channels ⁹Be(π^?, pd)X and ¹¹B(π^?, p ⁴He)X. On the basis of the results presented for ground-state parameters, it can be concluded that the binding energy of superheavy hydrogen isotopes decreases as the number of neutrons increases. Excited levels of the isotopes ⁵H and ⁶H are observed for the first time. On the energy scale, all of these states lie above the threshold for decay to free nucleons.     

High‐temperature study of superconducting hydrogen and deuterium sulfide

Hydrogen‐rich compounds are extensively explored as candidates for a high‐temperature superconductors. Currently, the measured critical temperature of 203 K in hydrogen sulfide (H₃S) is among the highest over all‐known superconductors. In present paper, using the strong‐coupling Eliashberg theory of superconductivity, we compared in detail the thermodynamic properties of two samples containing different hydrogen isotopes H₃S and D₃S at 150 GPa. Our research indicates that it is possible to reproduce the measured values of critical temperature 203 K and 147 K for H₃S and D₃S by using a Coulomb pseudopotential of 0.123 and 0.131, respectively. However, we also discuss a scenario in which the isotope effect is independent of pressure and the Coulomb pseudopotential for D₃S is smaller than for H₃S. For both scenarios, the energy gap, specific heat, thermodynamic critical field and related dimensionless ratios are calculated and compared with other conventional superconductors. We shown that the existence of the strong‐coupling and retardation effects in the systems analysed result in significant differences between values obtained within the framework of the Eliashberg formalism and the prediction of the Bardeen‐Cooper‐Schrieffer theory.     

Photonuclear reactions on molybdenum isotopes

The results of experimentally and theoretically studying the photodisintegration of molybdenum isotopes are presented. The yields of various photonucleon reactions on stable molybdenum isotopes were determined by the gamma-activation method. Use was made of bremsstrahlung photons from an electron accelerator that were characterized by the endpoint energies of 19.5, 29.1, and 67.7 MeV. Reactions involving the emission of up to three nucleons from the target nucleus were observed. The experimental results in question were compared with theoretical predictions based on the combined photonucleon-reaction model and obtained for 15 molybdenum isotopes. The relations between basic photonucleon reactions on the molybdenum isotopes considered in our present study were explained.     

Helium clustering in neutron-rich Be isotopes

Measurements of the helium-cluster breakup and neutron removal cross-sections for neutron-rich Be isotopes ^10–12,14Be are presented. These have been studied in the 30 to 42 MeV/nucleon energy range where reaction measurements are proposed to be sensitive to the cluster content of the ground-state wave-function. These measurements provide a comprehensive survey of the decay processes of the Be isotopes by which the valence neutrons are removed revealing the underlying – core-cluster structure. The measurements indicate that clustering in the Be isotopes remains important up to the drip-line nucleus ¹⁴Be and that the dominant helium-cluster structure in the neutron-rich Be isotopes corresponds to –Xn–.     

Effect of multisite traps on hydrogen transport in solids

The transport of hydrogen isotopes in solids is an important problem for a series of applications, in particular, for future thermonuclear reactors. The main processes determining transport are the diffusion of dissolved hydrogen and its interaction with lattice defects. It is known that vacancies in a metal can capture not only one hydrogen atom, but several at the same time. General equations describing hydrogen transport in this case are presented. Special attention is focused on the influence of this effect on the thermal desorption spectra. An experimental scheme making it possible to establish the capture of several atoms to traps is proposed.     

Ternary fission yields of 241Pu(nth,f)

Ternary events in the thermal neutron induced fission of ²⁴¹Pu(n,f) were studied with the recoil separator LOHENGRIN at the high-flux reactor of the Institut Laue Langevin in Grenoble. Yields and energy distributions could be determined for most isotopes of the elements hydrogen to oxygen. Also several heavier nuclei up to ³⁰Mg could be observed. Yields were measured for 42 isotopes, for further 17 isotopes upper limits could be deduced. For the first time the halo nuclei ¹¹Li, ¹⁴Be and ¹⁹C were found in neutron induced fission with yields of some 10⁻¹⁰ per fission.     

On beam intensity upgrade in the commercial cyclotrons of negative hydrogen ions

Compact isochronous cyclotrons to accelerate negative hydrogen ions of up to 30 MeV are widely used for production of medical isotopes and other applications. The physical and technical parameters of different accelerators are analyzed and compared. Measures to improve performance and to increase beam intensity are discussed. The text was submitted by the authors in English.     

Diffusion of hydrogen in metals

The present status of our understanding of the diffusion of hydrogen in metals, both experimental and theoretical, is reviewed. Discussions are focused on the mechanism of diffusion of hydrogen isotopes H, D and T in f.c.c. and b.c.c. metals; the positive muon (μ ⁺) is referred to where appropriate. An up-to-date compilation of diffusion data as a function of temperature and isotope mass has been made, and a clear distinction in general diffusion behaviour in f.c.c. and b.c.c. metals is noted. Subsequently, the results obtained from the Gorsky effect, nuclear magnetic resonance and quasi-elastic neutron scattering that provide information on elementary jump processes are discussed.

A conceptual framework of the quantum diffusion of light interstitials in metals is given, including the recent Kondo theory that emphasizes the crucial importance of particle-conduction electron interactions in the diffusion process, especially at low temperatures. It is shown with the help of recent estimates of the tunneling matrix element that the overall feature of diffusion of hydrogen isotopes in b.c.c. metals as well as μ ⁺ in f.c.c. metals can be explained consistently within the frame presented here.

Finally, recent advances in the diffusion studies on hydrogen in b.c.c. metals are described. They include a re-analysis of quench-recovery experiments that manifested nearly athermal diffusion of H, D and T in Ta at low temperatures, and an enormous enhancement of the diffusivity under stress (superdiffusion) observed for H and D in V.     

On dewetting dynamics of solid films of hydrogen isotopes and its influence on tritium ß spectroscopy

The dewetting dynamics of solid films of hydrogen isotopes, quench-condensed on a graphite substrate, was measured at various temperatures below desorption by observing the stray light from the film. A schematic model describing the dewetting process by surface diffusion is presented, which agrees qualitatively with our data. The activation energies of different hydrogen isotopes for surface diffusion were determined. The time constant for dewetting of a quench-condensed film at the working temperature of 1.86 K of the mainz neutrino mass experiment was extrapolated. Received 30 December 1999     

低能氢粒子沿不同角度轰击钨(001)表面的反射概率及入射深度分布的分子动力学研究

采用分子动力学方法对低能(0.5–50.0 eV)氢粒子 与钨表面的相互作用进行了模拟研究.研究发现, 当氢粒子垂直入射, 能量为0.5–20.0 eV时, 粒子滞留在钨内部的概率急速增加, 在整个模拟能量区间内, 发生反射过程的概率逐渐减少, 但反射过程始终占主导. 改变粒子的入射角度, 在某些能量范围内滞留概率虽有所增加, 但氢原子被反射现象仍然占主导. 通过进一步观察低能氢粒子在钨块内的入射深度和能量变化, 计算出其在钨块中的能量沉积分布. 这些结果对理解聚变反应中 钨材料的选用优势以及氢或氢同位素滞留有重大意义. 此外, 在所研究的能量范围内, 分子动力学方法的模拟结果与以二体理论为基础的TRIM程序的模拟结果之间有明显差异, 说明传统的二体碰撞理论不能很好地描述低能碰撞问题. 关键词： 面向等离子体材料 分子动力学方法 钨 氢