Shock-wave compression of hydrogen isotopes condensed under megabar pressures

Experiments on shock wave compression of solid hydrogen (protium) up to 66 GPa and deuterium (in the initially liquid or solid phase) up to 123 GPa using spherical devices where a steel ball (impactor) is explosion-accelerated to 23 km/s are described. The experimental data are compared with those obtained by American researchers for liquid deuterium and protium, who used conventional explosives and light-gas guns as energy sources in the experiments carried out on the Z machine at Sandia National Labs, where an impactor was accelerated by an ultrahigh magnetic field, or on the NOVA laser at the Livermore National laboratory. Our data agree well with those derived by Sandia Labs.     

Thermalization of muonic hydrogen in hydrogen targets

The thermalization of pµ atoms in protium and dµ atoms in deuterium is considered. Monte Carlo calculations are performed for gaseous (300 K) and solid (3 K) protium and deuterium targets. Complete sets of the total and differential cross sections for the scattering of pµ on protium targets and dµ on deuterium targets are used as an input to the Monte Carlo simulations. At 300 K, muonic atom scattering from single molecules of H₂ and D₂ is considered. In the case of solid hydrogen the correlation effects from all molecules of the sample are taken into account. In particular, the Bragg and phonon scattering cross sections are calculated. The spin states and average energy of the muonic atoms are shown as functions of time. It is shown that at energies below about 0.01 eV the solid-state effects influence strongly the calculated cross sections, and therefore the deceleration processes in the solids are much slower than in the gaseous targets. It is shown that the neutron spectrum due to ddµ formation and subsequent dd fusion is significantly affected by slow dµ thermalization in solid deuterium.     

Time-of-flight measurement of resonant molecular formation in muon-catalyzed dt fusion

Preliminary results are reported for an experiment at TRIUMF where a time-of-flight technique was tested for measuring the energy dependence of the rate for muon-catalyzed dt fusion. Muonic tritium atoms were created following transfer of negative muons from muonic protium in a layer of solid hydrogen (protium) containing a small fraction of tritium. The atoms escaped from the solid layer via the Ramsauer-Townsend mechanism, traversed a drift region of 18 mm, and then struck an adjacent layer of deuterium, where the muonic atom could form a molecular system. The time of detection of a fusion product (neutron or alpha) following muon arrival is dependent upon the energy of the muonic tritium atom as it traverses the drift region. By comparison of the time distribution of fusion events with a prediction based on the theoretical energy dependence of the rate, the strength of resonant formation can in principle be determined. The results extracted so far are discussed and the limitations of the method are examined.     

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)     

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.     

Time evolution of energy and spin state distribution of (pµ)1s atoms

Kinetic equations for muonic atoms in protium were solved using numerical methods. Distributions of muonic atoms on the energy and total spin were obtained.     

Charge transfer from the ground state of muonic hydrogen to at room temperature

The present status of research of muon transfer from the ground state of muonic protium to ⁴He is reviewed. The analysis of a recent measurement in a triple gas mixture of H₂+⁴He+Ne at 15 bar and room temperature is presented and the result is compared to the existing experimental and theoretical rates. The average muon transfer rate from protium to ⁴He determined from all lifetime measurements is . Received: 22 January 1998 / Revised: 4 March 1998 / Accepted: 31 March 1998     

连续碳纤维增强碳化硅的辐照效应

连续碳纤维增强碳化硅材料除了具有碳化硅材料固有的低中子活化性能,低衰变热性能和低氚渗透性能等优点以外,还具有密度低、线性膨胀系数小、高比强度、高比模量、耐高温、抗氧化、抗蠕变、抗热震、耐化学腐蚀、耐盐雾、优良的电磁波吸收特性等一系列优异性能,是各类核工程重要的潜在候选材料。在核聚变工程应用领域,连续碳纤维增强碳化硅材料作为第一壁材料不可避免地会受到各种辐射粒子的影响。研究清楚这些辐射粒子对它的辐照效应对其在核工程领域的安全使用至关重要。采用蒙特卡罗方法与分子动力学方法进行模拟计算,研究了氕、氘、氚和氦四种粒子对连续碳纤维增强碳化硅的辐照效应。SRIM和LAMMPS计算结果表明:当入射原子能量为100 eV,连续碳纤维增强碳化硅中碳的浓度在80%~85%时,氕、氘、氚和氦原子的溅射率存在最小值;入射粒子的种类对溅射率的影响显著,氦原子的溅射率大于氘原子和氚原子,而氘原子和氚原子的溅射率相差不大但均显著大于氕原子;溅射率随入射能量的增加先迅速增加后逐渐减小,氕、氘、氚和氦原子入射能量分别在200,400,600和800 eV时存在溅射率最大值;当氦原子入射能量为100 eV时,溅射率随入射角度的增加而逐渐减少。这些结果对连续碳纤维增强碳化硅材料在核工程上的应用具有一定的参考意义。Continuous carbon fiber reinforced silicon carbide material has the low neutron activation, low decay heat performance and tritium permeability, which are inherent performance of silicon carbide materials. It also has other advantages such as low density, small linear expansion coefficient, specific strength and specific modulus, high temperature resistance, oxidation resistance, creep resistance, thermal shock, resistance to chemical corrosion, salt fog resistance, excellent electromagnetic wave absorption properties, etc. It is an important potential candidate material in various field of nuclear engineering. In the field of nuclear fusion engineering applications, continuous carbon fiber reinforced silicon carbide as the first wall material will inevitably be bombarded by a variety of radiation particles. The radiation effect is critical to its safe use in nuclear engineering. The Monte Carlo method and the molecular dynamics method were used to study the radiation effect of protium, deuterium, tritium and helium on continuous carbon fiber reinforced silicon carbide. The SRIM and LAMMPS simulation results show that when the incident energy is 100 eV and the concentration of carbon in the continuous carbon fiber reinforced silicon carbide is about 80% ~ 85%, the sputtering yield of protium, deuterium, tritium and helium atoms have the minimum values. The kind of incident particle has a significant effect on the sputtering yield. The sputtering yield of helium atoms is larger than that of tritium atoms and deuterium atoms. There is not much difference between the sputtering yield of deuterium atoms and tritium atoms, and both the sputtering yield of deuterium atoms and tritium atoms are larger than that of protium atoms. The sputtering yield initially increases rapidly with the increase of the incident energy and then decreases gradually. The incident energy of the protium, deuterium, tritium and helium atoms has the maximum value of the sputtering yield at 200, 400, 600 and 800 eV, respectively. When the incident energy of helium atoms is 100 eV, the sputtering yield decreases while the increase of the incident angle. These results can provide a certain reference for the application of continuous carbon fiber reinforced silicon carbide materials in nuclear engineering.     

On the Energy Dependence of the Rate of Muon Transfer from Proton to Oxygen

Physics of Atomic Nuclei - The results obtained by calculating the rate of muon transfer from the $$1s$$ state of muonic protium to a free-oxygen nucleus in the collision-energy range between...     

Muon molecular formation and transfer rate in solid hydrogen-deuterium mixtures

In an experiment at TRIUMF to study muon-catalyzed fusion and associated atomic and molecular effects, negative muons were stopped in a solid protium hydrogen layer containing a small amount of deuterium. Most of the resulting µp atoms disappeared by formation of ppµ molecules or by muon transfer to a deuteron. The µd can drift almost freely through the hydrogen layer due to the Ramsauer-Townsend effect and may even leave the layer. If a thin neon layer is frozen atop the hydrogen, the exiting muonic atoms will very rapidly release their muon to a neon atom. The analysis of the time structure of the neon X-rays is used to determine the rates of the slower processes involved in the evolution of the µp. This analysis has been performed with the help of Monte Carlo calculations, which simulate the kinetics of both µp and µd atoms in the hydrogen mixtures.     

High-Pressure Hydrogen Isotopes Sources Based on Vanadium Hydride

Equilibrium pressures of protium and deuterium desorption over a two-phase area of monohydride-vanadium dihydride were measured. Temperature measurement range was 300–635 K and the pressure range 1–500 MPa. Obtained temperature-dependences of fugacities within the given measurement range are: lgf(MPa) = −2152/T+ 6.6 and lgf(MPa) = −2575/T + 7.4 for protium and deuterium, respectively. The values of enthalpy and entropy for vanadium dihydride phase formation were calculated from obtained relations. Using expressions obtained for fugacities and literature data on hydrogen imperfection the pressures, which can be obtained with vanadium dihydride employed in thermodesorption hydrogen sources, were estimated. Taking into account that due to deterioration in strength properties of the used structural materials, the heating temperature of the load-bearing body is limited to ∼973 K, maximal calculated pressure, which can be obtained with such sources as ≈1820 MPa for protium and ≈2220 MPa for deuterium. This revised version was published online in August 2006 with corrections to the Cover Date.     

Muon transfer from protium to helium

Muon transfer from hydrogen isotopes to helium is of importance in muon-catalyzed fusion and serves as a unique tool for the direct observation of the mesomolecular ion (pµHe)^*. During two data-taking runs in 1994 and 1995 at PSI, measurements of the transfer from protium to helium were carried out using CCD's and Ge-diodes as independent X-ray detectors to obtain information on the time distribution and intensity of the 7 keV decay X-ray of the mesomolecular ion. Dual¹H₂ +⁴ He and triple¹H₂ + Ne +^3,4He gas mixtures at low temperatures were investigated to extract transfer rates. Protium of high purity was available. For the first time a transfer rate from muonic protium to³He was measured. A general survey of our measurements and preliminary analysis is presented.     

Measurement of muon transfer rate λpt and molecular formation rate λppµ, in solid hydrogen targets,in solid hydrogen targets

The knowledge of muon transfer from protium to tritium is essentially theoretical and the different theoretical values disagree partially. Using solid hydrogen-tritium targets, with different tritium concentrations, we obtained precise experimental results for the transfer rate to tritium and the ppµ molecular formation rate. The time spectra of neutrons and alpha particles produced after dtµ fusion are used to determine the transfer rate _pt and the molecule formation rate _ppµ.     

Dynamics of muonic atom cascade in hydrogen-helium mixtures

The deexcitation of excited muonic protium and deuterium in the mixture of hydrogen and helium isotopes is considered. Methods of experimental determination of the probability of direct atomic muon capture by hydrogen and muon transfer rates from excited muonic hydrogen to helium are proposed. Theoretical results for the population of the muonic atoms in the ground state, , are compared with the existing experimental data. Results obtained for mixtures are of interest for investigation of nuclear fusion in muonic molecules. Received: 6 August 1998 / Revised: 1st October 1998 / Accepted: 2 October 1998     

Muon transfer from protium to helium isotopes at low temperature

The transfer reaction of negative muons from muonic protium to ³ and ⁴ in binary and triple gas mixtures was studied. In the binary mixtures the transfer rates to the two helium isotopes were determined from the time distribution of the 7-keV X-rays of the intermediate muonic molecule (pμHe)*. The experimental transfer rate to ⁴ is in good agreement with theoretical predictions, whereas the rate to ³ is a factor 2 to 3 smaller than the predicted ones. Radiative branching ratios of the (pμHe)8 molecular decay were obtained. Muon transfer from excited states of muonic protium gives the main contribution to the total intensity of the μHe Lyman series in the binary mixtures. Values of q _1s ^He are determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

Isotopic effects in the muon transfer from pmu and dmu to heavier atoms

The results of accurate hyperspherical calculations of the muon-transfer rates from muonic protium and deuterium atoms to nitrogen, oxygen, and neon are reported. Very good agreement with measured rates is obtained and, for the three systems, the isotopic effect is perfectly reproduced. The transfer rate is higher for deuterium in the cases of nitrogen and neon due to constructive interferences between two transfer paths. The lower transfer rate for deuterium in the case of oxygen results from a large resonant contribution.     

Experimental confirmation of the predicted shallow donor hydrogen state in zinc oxide

We confirm the recent prediction that interstitial protium may act as a shallow donor in zinc oxide, by direct spectroscopic observation of its muonium counterpart. On implantation into ZnO, positive muons--chemically analogous to protons in this context--form paramagnetic centers below about 40 K. The muon-electron contact hyperfine interaction, as well as the temperature and activation energy for ionization, imply a shallow level. Similar results for the cadmium chalcogenides suggest that such shallow donor states are generic to the II-VI compounds. The donor level depths should serve as a guide for the electrical activity of interstitial hydrogen.     

高压下FCC相金属氢结构稳定性和非谐效应的理论研究

利用第一性原理分子动力学方法研究金属氢体系的非简谐效应, 给出金属氢的声子谱, 讨论金属氢声子谱的温度效应。计算得到氢的同位素氕、氘和氚的FCC相在非零温下的声子谱, 不同温度下的声子谱对比发现零温下3.6 TPa为热力学稳定的临界压强点, 而有限温度下(100 K)临界压强点降到2.8 TPa, 非简谐效应显著地改变了体系的结构稳定性和声子振动性质。     

Recent experiments on muon transfer in gas mixtures

The experimental muon transfer rates from muonic protium and deuterium to heavier elements show a complexZ dependence. Instead of the expected monotonicZ dependence considerable variations between neighboring elements are observed. Transfer to neon has a specially small rate. Furthermore, the time distribution of the muonic X-rays shows in a number of molecules a complex structure, and depends in the case of a H₂ + CH₄ gas mixture also on the total pressure.     

Present status of the investigation on muon transfer in gaseous mixtures of hydrogen and oxygen

To investigate the energy dependence of muon transfer to oxygen, we performed measurements in gaseous mixtures of hydrogen and oxygen. The time distributions of the muonic oxygen X-rays showed the same structure as the one observed earlier in H₂+SO₂ mixtures. In the delayed part of these distributions, one can distinguish a short-time and a long-time component. From the latter, we deduced the transfer rates from thermalized muonic protium, respectively deuterium, to oxygen. The short-time component can be interpreted as being due to muon transfer from epithermal muonic hydrogen atoms. The time parameters are characteristic for the deceleration process as well as for energy-dependent transfer rates. With results of recent research on the formation and the thermalization of muonic hydrogen, we performed Monte Carlo simulations in order to test the hypothesis of an energy-dependent transfer rate.