Search results for "Clusters"
showing 10 items of 1274 documents
Stability chart of small mixed4He−3Heclusters
2003
A stability chart of mixed ${}^{4}\mathrm{He}$ and ${}^{3}\mathrm{He}$ clusters has been obtained by means of the diffusion Monte Carlo method, using both the Aziz HFD-B and the Tang-Toennies-Yiu atom-atom interaction. The investigated clusters contain up to eight ${}^{4}\mathrm{He}$ atoms and up to 20 ${}^{3}\mathrm{He}$ atoms. One single ${}^{4}\mathrm{He}$ binds 20 ${}^{3}\mathrm{He}$ atoms, and two ${}^{4}\mathrm{He}$ bind 1, 2, 8, and more than 14 ${}^{3}\mathrm{He}$ atoms. All clusters with three or more ${}^{4}\mathrm{He}$ atoms are bound, although the combinations ${}^{4}{\mathrm{He}}_{3}^{3}{\mathrm{He}}_{9,10,11}$ and ${}^{4}{\mathrm{He}}_{4}^{3}{\mathrm{He}}_{9}$ are metastable. …
Helium bubbles in metals: Molecular-dynamics simulations and positron states.
1987
By combining molecular-dynamics results for the aluminum-helium interface with positron-state calculations it is demonstrated that a positron is trapped at the surface of a He bubble in Al. The annihilation rate with Al electrons is similar to that at a clean surface, while simultaneously there is a significant annihilation rate with He electrons. This enables one to obtain a useful relation between the positron lifetime and helium densities in bubbles.
Cluster growth with long-range interactions
1996
Abstract Growth models in which the morphology depends on interactions of the type V(r) = C r n are presented. The growth algorithms are generalizations of DLA. The particles diffuse on a triangular lattice and eventually either stick to the cluster or are lost. Several processes are simulated in this way: in one case only pure sticking is taken into account, in another case evaporation and rearrangement are also allowed to occur. In the former case (with attractive interactions) the clusters exhibit a highly symmetric shape (a sixfold star) whose detailed structure depends on n , C kT , and time. In the latter case (studied with repulsive dipolar interactions) the tendency to ramification …
Minimal mass size of a stable He-3 cluster
2005
The minimal number of 3He atoms required to form a bound cluster has been estimated by means of a Diffusion Monte Carlo procedure within the fixed-node approximation. Several importance sampling wave functions have been employed in order to consider different shell-model configurations. The resulting upper bound for the minimal number is 32 atoms.
A note on Δn ≠ 0 Stark transitions in hydrogenlike atoms
1992
In a gaseous helium or hydrogen target slow muons or antiprotons are captured into orbits with a high principal quantum number (n = 15 to 50) to form (μ− α)+ ions, (pα)+ ions, or (pp) atoms respectively. In the subsequent deexcitation process Stark mixing of the intermediary states plays an important role. The successful Mainz Cascade Model assumed Δn = 0 for the Stark transitions, although formally no such selection rule exists. This note examines the reasons why Δn ≠ 0 Stark transitions play only a negligible role in the deexcitation cascade.
Momentum partition between constituents of exotic atoms during laser-induced tunneling ionization
2015
The tunneling ionization of exotic atoms such as muonic hydrogen, muonium, and positronium in a strong laser field of circular polarization is investigated, taking into account the impact of the motion of the center of mass on the the tunneling ionization dynamics. The momentum partition between the ionization products is deduced. The effect of the center-of-mass motion for the momentum distribution of the ionization components is determined. The effect scales with the ratio of the electron (muon) to the atomic core masses and is nonnegligible for exotic atoms, while being insignificant for common atoms. It is shown that the electron (muon) momentum shift during the under-the-barrier motion…
High-order harmonic generation in fullerenes using few- and multi-cycle pulses of different wavelengths
2012
We present the results of experimental and theoretical studies of high-order harmonic generation (HHG) in plasmas containing fullerenes using pulses of different duration and wavelength. We find that the harmonic cutoff is extended in the case of few-cycle pulses (3.5 fs, 29th harmonic) compared to longer laser pulses (40 fs, 25th harmonic) at the same intensity. Our studies also include HHG in fullerenes using 1300 and 780 nm multicycle (35 and 40 fs) pulses. For 1300 nm pulses, an extension of the harmonic cutoff to the 41st order was obtained, with a decrease in conversion efficiency that is consistent with theoretical predictions based on wave packet spreading for single atoms. Theoreti…
Molecular polarizability of semiconductor clusters and nanostructures
2002
Abstract The interacting-induced-dipoles polarization model implemented in program PAPID is used for the calculation of the molecular dipole–dipole polarizability α . The method is tested with Si n , Ge n and GanAsm small clusters. On varying the number of atoms, the clusters show numbers indicative of particularly polarizable structures. The results for the polarizability are in agreement with reference calculations from Chelikowsky. The bulk limit for the polarizability is estimated from the Clausius–Mossotti relationship. The polarizability trend for these clusters as a function of size is different from what one might have expected. The clusters are all more polarizable than what one mi…
Enhanced nuclear Schiff moment in stable and metastable nuclei
2019
Nuclei with static intrinsic octupole deformation or a soft octupole vibrational mode lead to strongly enhanced collective nuclear Schiff? moments. Interaction between electrons and these Schiff moments produce enhanced time reversal (T) and parity (P) violating electric dipole moments (EDM) in atoms and molecules. Corresponding experiments may be used to test CP-violation theories predicting T,P-violating nuclear forces and to search for axions. Nuclear octupole deformations are predicted in many short lived isotopes. This paper investigates octupole deformations in stable and very long lifetime nuclei such as 153Eu, 235U, 237Np and 227Ac, which can ease atomic experiments substantially. T…
Separation of proton polarizabilities with the beam asymmetry of Compton scattering
2013
We propose to determine the magnetic dipole polarizability of the proton directly from the beam asymmetry of low-energy Compton scattering based on the fact that the leading non-Born contribution to the asymmetry is due to the magnetic polarizability alone; the electric polarizability cancels out. The beam asymmetry thus provides the simplest observable with a clean separation of the magnetic polarizability from the electric one. Introducing polarizabilities in a Lorentz-invariant fashion we compute the higher-order (recoil) effects of polarizabilities on beam asymmetry and show that these effects are most suppressed in forward kinematics. With the prospects of precision Compton experiments…