Deceleration of muonic hydrogen atoms in solid hydrogens

Results of recent calculations of cross-sections for muonic hydrogen atom scattering in solid hydrogen isotope targets are presented. The coherent parts of these cross-sections, namely, the elastic Bragg scattering and phonon coherent scattering, are calculated accurately for the first time. A fine structure of Bragg peaks is obtained in the case of Bravais fcc structure of hydrogen targets frozen rapidly at 3 K. The one-phonon coherent cross-section is estimated using the Debye approximation. The calculated differential cross-sections are used for Monte Carlo simulations of muonic atom diffusion and slowing down in solid hydrogens. Also is calculated the energy-dependent rate of resonant ddμ molecule formation in 3 K solid deuterium quantum crystal, using the Debye model and Van Hove's formalism of the response function. This rate is very different from that obtained for the 3 K gas model. The influence of dμ atom slowing down on the average ddμ formation rate is considered. It is shown that very slow dμ deceleration below 10 meV is important for explanation of experimental results. This revised version was published online in August 2006 with corrections to the Cover Date.     

Scattering of muonic hydrogen atoms

Our measurement compares the energy dependence of the scattering cross-sections of muonic deuterium and tritium on hydrogen molecules for collisions in the energy range 0.1–45 eV. A time-of-flight method was used to measure the scattering cross-section as a function of the muonic atom beam energy and shows clearly the Ramsauer–Townsend effect. The results are compared with theoretical calculations by using Monte Carlo simulations. The molecular pdμ and ptμ formation creates background processes. We measure the formation rates in solid hydrogen by detecting the 5.5 MeV (pdμ) and 19.8 MeV (ptμ) γ-rays emitted during the subsequent nuclear fusion processes. This revised version was published online in August 2006 with corrections to the Cover Date.     

水中ClF的分子动力学模拟:液体中的卤键作用

Does the halogen bonding interaction co-exist in liquid when it competes with the hydrogen bonding interaction? The classical molecular dynamics simulations for the solvation properties of ClF molecule in water are performed with the Lennard-Jones plus Coulomb electrostatic potential parameters that are optimized with ab initio interaction energy calculations for the pre-reactive H₂O…ClF complex. We find that the halogen bonding interactions occur between O and Cl atoms and have the comparable strength and population with respect to the hydrogen bonding interactions of Cl…H.     

Charge exchange and Coulomb de-excitation of muonic atoms in low energy collisions

The muon transfer and Coulomb de-excitation rates at the collisions of (pμ) _n , (dμ) _n and (tμ) _n muonic atoms in excited states n = 3, 4, 5 with hydrogen isotopes p, d, t are calculated for all possible combinations of hydrogen isotopes. The advanced adiabatic approach (AAA) [1–3] is adapted and used to the specific case of muonic atom collisions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Muon transfer from ground state deuterium to helium nuclei and its temperature dependence

The energy and time distributions of the decay X-rays of excited, metastable, molecular (dμHe)*-resonances were measured. The comparison of the observed energy spectra with calculated ones suggests that decay from the rotational state J = 1 dominates at the investigated conditions. The muon transfer rates from ground state deuterium to the helium isotopes ³He and ⁴He at low temperatures were determined from the time distributions of these spectra. Additionally, the temperature dependence of the muon transfer rate was clearly established in deuterium / ⁴He mixtures. This revised version was published online in August 2006 with corrections to the Cover Date.     

Unconventional Energy Bands and Chirality of Ultracold Atoms in Trilayer Honeycomb Lattice

We investigate ultracold fermionic atoms in the trilayer honeycomb lattice. In the low energy approximation, we derive an effective Hamiltonian for pseudospins. The energy spectrum shows a cubic form of the wavevector and is gapless. The quasiparticles and quasiholes are ehiral and show Berry＇s phase π when the wavevector adiabatically evolves along a closed circle, Furthermore, the experimental detection of the energy spectrum is proposed with Bragg scattering techniques.     

Historical overview and introduction

The complex balance of processes occurring at the cascade of exotic H-atoms is usually described by the so-called standard cascade model, but this model neglects variations of the kinetic energy T of the exotic atom during the cascade which are crucial for the analysis of several important experiments. New experimental results on T _μp at H₂ pressures between 0.063 and 4 hPa demonstrate the importance of acceleration due to Coulomb de-excitation processes at highly excited μp levels n > 9. The data at the lowest density are sensitive to the initial values of the kinetic energy and n-levels at the moment of atomic capture. From the measured low-energy tail of the T _μp-distribution it can be concluded that a considerable part of the μp(2s) atoms is metastable at pressures of a few hPa. This revised version was published online in August 2006 with corrections to the Cover Date.     

Short-ranged potential effects on the recurrence spectra of lithium M = 1 atoms in parallel electric and magnetic fields

This paper presents recurrence spectra of highly excited lithium atoms with M = 1 state in parallel electric and magnetic fields at a fixed scaled energy ε = -0.03. Short-ranged potentials including ionic core potential and centrifugal barrier are taken into account. Their effects on the states and photo-absorption spectrum are analysed in detail. This demonstrates that the geometric features of classical orbits are of special importance for modulations of the spectral pattern. Thus the weak polarization as well as the reduction of correlation of electrons induced by short-ranged potentials give rise to the recurrence spectra of lithium M = 1 atoms more compact than that of the M = 0 one, which is in good agreement with the experimental prediction.     

The effect of anti-hydrogen bond on Fermi resonance: A Raman spectroscopic study of the Fermi doublet ν1—ν12 of liquid pyridine

The effects of anti-hydrogen bond on the ν₁—ν₁₂ Fermi resonance (FR) of pyridine are experimentally investigated by using Raman scattering spectroscopy. Three systems, pyridine/water, pyridine/formamide, pyridine/carbon tetrachloride, provide varying degrees of strength for the diluent-pyridine anti-hydrogen bond complex. Water forms a stronger anti-hydrogen bond with pyridine than with formamide, and in the case of adding non-polar solvent carbon tetrachloride, which is neither a hydrogen bond donor nor an acceptor and incapable of forming hydrogen bond with pyridine, the intermolecular distance of pyridine will increase and the interaction of pyridine molecules will reduce. The dilution studies are performed on the three systems. Comparing with the values of Fermi coupling coefficient W of the ring breathing mode ν ₁ and triangle mode ν ₁₂ of pyridine at different volume concentrations, which are calculated according to the Bertran equations, in three systems, we find that the solution with the strongest anti-hydrogen bond, water, shows the fastest change in the ν₁—ν₁₂ Fermi coupling coefficient W with the volume concentration varying, followed by the formamide and carbon tetrachloride solutions. These results suggest that the stronger anti-hydrogen bond-forming effect will cause a greater reduction in the strength of the ν₁—ν₁₂ FR of pyridine. According to the mechanism of the formation of anti-hydrogen bond in the complexes and the FR theory, a qualitative explanation for the anti-hydrogen bond effect in reducing the strength of the ν₁—ν₁₂ FR of pyridine is given.     

1-戊基的紫外光解动力学

The ultraviolet (UV) photodissociation of jet-cooled 1-pentyl radical is investigated in the wavelength region of 236-254 nm using the high-n Rydberg-atom time-of-flight (HRTOF) technique. The H-atom photofragment yield spectrum of the 1-pentyl radical shows a broad UV absorption feature peaking near 245 nm, similar to the 2p_z→3s absorption bands of ethyl and n-propyl. The center-of-mass translational energy distribution, P(E_T), of the H+C₅H₁₀ product channel is bimodal, with a slow peak at~5 kcal/mol and a fast peak at~50 kcal/mol. The fraction of the average translational energy release in the total available energy, 〈f_T〉, is 0.30, with those of the slow and fast components being 0.13 and 0.58, respectively. The slow component has an isotropic product angular distribution, while the fast component is anisotropic with an anisotropy parameter~0.4. The bimodal translational energy and angular distributions of the H+C₅H₁₀ products indicate two H-atom elimination channels in the photodissociation of 1-pentyl:(i) a direct, prompt dissociation from the electronic excited state and/or the repulsive part of the ground electronic state potential energy surface; and (ii) a unimolecular dissociation of internally hot radical in the ground electronic state after internal conversion from the electronic excited state.     

Solvent effects on the S0→S2 absorption spectra of β-carotene

Absorption spectra of β -carotene in 31 solvents are measured in ambient conditions. Solvent effects on the 0--0 band energy, the bandwidth, and the transition moment of the S₀ → S₂ transition are analysed. The discrepancies between published results of the solvent effects on the 0--0 band energy are explained by taking into account microscopic solute-solvent interactions. The contributions of polarity and polarizability of solvents to 0--0 band energy and bandwidth are quantitatively distinguished. The 0--0 transition energy of the S₂ state at the gas phase is predicted to locate between 23000 and 23600~cm^-1.     

A unified scheme for flavoured mesons and baryons

The masses of mesons and baryons with various flavour combinations for qˉq, qˉQ, QˉQ, qqq, qqQ, qQQ, QQQ etc. are computed using a confinement scheme based on harmonic approximation with Lorentz scalar plus vector character. The residual two body coulombic interactions and the spin-hyperfine interactions of the confined one gluon exchange effects are perturbatively calculated and added to the confinement energy to get the mass of the hadron. With all the parameters fixed to get ground state masses of hadrons containing like flavour combinations, a parameter free prediction of the leptonic decaywidths of vector mesons and their sizes are being made. Our results on the baryonic and mesonic masses with open flavours and the predictions on the leptonic decay widths are in good agreement with the respective experimental values. Received: 26 February 1998 / Revised version: 1 September 1998     

Muon transfer in dµ + H2 collisions

The impact of excited state muon transfer in dμ + H₂ collisions has been investigated. The formation of metastable pdμ^* molecules and their subsequent decay into the pμ (1s) + d channel opens a transfer channel that is otherwise closed at the n=2 level. This mechanism enlarges the fraction of muons arriving to the ground state of the lighter isotope. The resulting ground state population P _1s ^pμ as function of deuterium concentration appears to be in qualitative agreement with recent measurements of the K _α X-ray yield in H₂/D₂ mixtures. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of vacuum polarization and of proton polarizability in the Lamb shift of muonic hydrogen

The contributions to the Lamb shift in muonic hydrogen from hadronic vacuum polarization and from the correction associated with electron vacuum polarization and with the proton polarizability are calculated by using present-day experimental data on the cross section for e ⁺ e ⁻ annihilation into hadrons and on structure functions for deep-inelastic ep scattering. The numerical value of the total contribution to the (2P-2S) shift in muonic hydrogen is found to be 10.95 μeV. __________ Translated from Yadernaya Fizika, Vol. 64, No. 7, 2001, pp. 1358–1363. Original Russian Text Copyright ? 2001 by Martynenko, Faustov.     

Study of Borromean halo nuclei by the neutron wall with simulation

The model of three-body Borromean halo nuclei breakup was described by using standard phase space distributions and the Monte Carlo simulation method was established to resolve the detection problem of two neutrons produced from breakup reaction on the neutron wall detector. For ⁶He case,overall resolution σE_k for the Gaussian part of the detector response and the detection efficiency including solid angle acceptance with regard to the excitation energy E_k are obtained by the simulation of two neutrons from ⁶He breakup into the neutron wall. The effects of the algorithm on the angular and energy correlations of the fragments are briefly discussed.     

Role of Ga-doping in ironben gallium alloy clusters

The structural and magnetic properties of Fe_n-mGa_m (n=3～6, m=0～2; n=13, m=0～3) alloy clusters have been studied using density functional theory. The substitutional doping is favourable for small clusters with up to six atoms at low Ga concentration and substitutional Ga atoms in 13-atom clusters prefer surface sites. The Ga-doping generally could reduce the energetic stability but enhance the electronic stability of Fe clusters, along with a decrease of the local magnetic moments of Fe atoms around Ga dopants. These findings provide a microscopic insight into Fe-Ga alloys which are well-known magnetostriction materials.     

电子与正电子散射的辐射修正

With the Mφller's theory of scattering between the electrons and the Dirac's hole theory, Bhabha has obtained the formula for the scattering of the electrons and the positrons. The experimental evidence of this phenomenon was discovered by Ho (何泽慧), and she has studied this phenomenon by means of the β⁺-radioactivity of the β⁺ sources such as Mn⁵², and F¹⁸ in the cloud chamber. The comparison of the theory and the experiment was done (see reference [2], [3], [4], [5] and [6].) by Ho, O. Ritter et al, R. R. Roy and L. Groven, G. R. Hoke and A. Ashkin et al.The purpose of the present work is to show the effect of the radiative corrections to the scattering of the electrons and the positrons by the method in the quantum electrodynamics developed by S. Tomonaga, J. Schwinger, R. P. Feynman and F. J. Dyson.In the above-mentioned electron and positron scattering experiments, the contributions to the scattering cross-section are mostly due to the positrons of low energies (about 0.1 to 0.2 Mev). In this energy range, the exchange effect in Bhabha's theory is small. In this work for the radiative corrections to the scattering of the electrons and the positrons, we have neglected this exchange effect. The ratio of the correction of the scattering cross-section due to the radiative corrections to the scattering cross-section of Bhabha's theory at this energy range does not exceed 1%. For experiments of the low energy positrons and of the higher energy positrons (e.g positrons with energies of 0.5 Mev to 1 Mev as in the experiment of Ashkin et al) with small exchanges of energy between the electrons and the positrons during scattering, our calculation is adequate. But for positrons of higher energies and with large exchanges during scattering, our calculation should be improved by considering the exchange effect.     

Effect of Hydrogen Implantation on SIMOX SOI Materials

Hydrogen ions were implanted into separation by implantation of oxygen (SIMOX) silicon-on-insulator (SOI) wafers near the oxygen-implantation-induced damage peak under different conditions of energy and dose. It was found that the implanted hydrogen ions not only accelerate the diffusion of oxygen atoms from the annealing ambience into the wafer but also cause an outward diffusion of oxygen atoms in the buried oxide (BOX) layer. Thus, greatly broadened buried oxygen-rich (BOR) layers were formed in our experiments, which are 18%-79% broader than the BOX layer of standard SIMOX SOI wafers under the same conditions of oxygen implantation. The mechanism was discussed. A potential low cost method to fabricate SIMOX SOI wafers is proposed.     

On singularity-free spacetimes

We consider here the metric for the singularity-free family of fluid models. The metric is unique for cylindrically symmetric space-time with metric potentials being separable functions of radial and time coordinates in the comoving coordinates. It turns out that fluid models separate out into two classes, withρ ≠μp in general butρ = 3p in particular andp =ρ. It is shown that in both the cases radial heat flow can be incorporated without disturbing the singularity-free character of the spacetime. The geodesics of the singularity-free metric are studied and the geodesic completeness is established. Several previously known solutions are derived as particular cases.     

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.