Interatomic electronic decay in endohedral fullerenes

Ionization of an atom in an endohedral fullerene complex can lead to a wealth of nonradiative decay processes. These interatomic processes occur due to the correlation existing between the atomic and the fullerene electrons and do not take place in the free species . Considering as an example, we calculate the rates of the interatomic decay processes and show that the interatomic decay in is ultrafast. Moreover, our analysis suggests that interatomic decay in an endohedral fullerene does not necessarily lead to the destruction of the complex.     

Interatomic coulombic decay in van der waals clusters and impact of nuclear motion

It is demonstrated that excited van der Waals systems can relax by electron emission via a novel interatomic mechanism. The process is analyzed by means of extensive ab initio calculations of potential energy surfaces and electronic decay rates. The electronic emission, taking place on the same time scale as the motion of the atomic nuclei, is accompanied by interesting dynamical effects amenable to experimental observations. These effects arise as a consequence of the weak chemical bond in van der Waals clusters and the Coulomb repulsion pattern originating from electron emission.     

Metastable electronic states induced by nuclear decay and light

Radioactive atoms incorporated in insulating solid-state compounds create various kinds of chemical and physical after-effects upon nuclear disintegration. Mössbauer emission spectroscopy of⁵⁷Co-labelled coordination compounds has undoubtedly become the most informative technique to detect such after-effects like aliovalent charge and spin states of the nucleogenic iron atom resulting from the⁵⁷Co(EC)⁵⁷Fe decay, low energy excitations of crystal field and Zeeman states, linkage isomerism, radical formation with subsequent redox reactions, and others. We have extensively studied⁵⁷Co-labelled complexes with [Co^IIN₆] cores employing time-integral and time-resolved Mössbauer emission spectroscopy. In complexes of strong ligands fields (where the corresponding synthesized iron(II) complexes show low spin behaviour with¹A₁ ground slate) and in complexes of intermediate ligand field strength (where the corresponding iron(II) compounds exhibit thermal spin-crossover¹A₁ ⁵T₂) we have observed the population of metastable high spin states, which is strongly time- and temperature-dependent in the case of the strong-field complexes. Irradiation of iron(II) spin-crossover complexes with light also induces the formation of metastable high spin states, which are the same in nature as those resulting from decaying nuclei as an intramolecular light source. The mechanisms for light-induced excited spin state trapping (LIESST) and nuclear decay induced excited spin state trapping (NIESST) have been elucidated; they are strongly related to each other. In⁵⁷Co-labelled LiNbO₃ and other matrices, we have observed nonthermalized populations of the Zeeman sublevels of the ligand field ground state. These low energy excitations and the metastable ligand field states constitute the last stages of the slowing down process after the nuclear decay.     

Dynamic electronic after-effects of nuclear decay in Mössbauer resonances

A theory has been constructed for the effect of a decaying atomic state on the Mössbauer line shapes. A most general case has been considered in which the nucleus interacts with its surroundings via electric monopole as well as electric quadrupole and magnetic dipole coupling, and the decay of the excited atomic state results in a change in the direction of the quantization axis.     

Theorem relating spatial and temporal harmonics for nuclear interlevel transfer driven by collective electronic oscillation

A crucial step in the development of gamma-ray lasers will be the discovery of an efficient mechanism for nuclear interlevel transfer. One promising mechanism uses the near-field interaction between the nucleus and laser-driven collective electronic oscillations. I prove an important theorem relating spatial and temporal harmonics: 2²ⁿ-poles are driven only at even multiples of the laser frequency, while 2²ⁿ⁺¹-poles are driven only at odd multiples of the laser frequency. I comment on the theorem's relevance to a proposed interlevel-transfer experiment.     

Microscopic nuclear collective motion studied by classical equations of motion

The time-dependent variation principle is used to obtain generally non-canonical equations of motion from any class of quantum states which are parameterized by a set of continuous complex quantities. A class of states is presented whose associated classical dynamics is described by the five collective quadrupole degrees of freedom. Information about the classical dynamics of the system can be obtained from the non-canonical equations by finding physically interesting quantities which are coordinate independent and which characterize the low-energy collective motion. Approximate collective hamiltonians, of either a Bohr-Mottelson or an IBM type, can be found by insisting that the interesting physical quantities which describe the low-energy classical behavior of the many-body system are the same as those describing the classical behavior of the system given by the collective hamiltonian. The method is applied to two simple schematic models, one vibrational and one rotational, and IBM hamiltonians are obtained.     

Lateral motion of SiGe islands driven by surface-mediated alloying

SiGe islands move laterally on a Si(001) substrate during in situ postgrowth annealing. This surprising behavior is revealed by an analysis of the substrate surface morphology after island removal using wet chemical etching. We explain the island motion by asymmetric surface-mediated alloying. Material leaves one side of the island by surface diffusion, and mixes with additional Si from the surrounding surface as it redeposits on the other side. Thus the island moves laterally while becoming larger and more dilute.     

Quantum interferences in nuclear decay

At nuclear level mixing condition, interferences between different transition amplitudes can occur. In a narrow frequency range, absorption can be hindered while not the emission. This feature offers interesting applications on the design of a graser and of a resonant scatterer for -rays.     

Baryon number violating nuclear decay

The expressions for baryon number violating nuclear partial decay widths are derived from the interactions as predicted by grand unified theories. Theory predicts that the baryon number violating proton decay inside the nucleus is hindered relative to the free proton decay rate. In the case of closed shell nuclei, the meson spin-isospin dependence of the partial width is the same as that for the nucleon decay. The branching ratios of decay amplitudes depend on the nuclear binding energies. Nuclear structure introduces lepton energy spread of ±49.5 MeV for light closed shell nuclei, while it does not affect the back to back emission of lepton-meson pair.     

Prospects for coherently driven nuclear radiation by Coulomb excitation

Possible experiments are discussed in which Coulomb excitation of nuclear isomers would be followed by sequential energy release. The possibility of coherent Coulomb excitation of nuclei ensconced in a crystal by channeled relativistic heavy projectiles is considered. The phase shift between neighbor-nuclei excitations may be identical to the photon phase shift for emission in the forward direction. Thus, the elementary string of atoms may radiate coherently with emission of characteristics nuclear γ rays, and the intensity of the radiation would be increased due to the summation of amplitudes. Mössbauer conditions should be important for this new type of collective radiation, which could be promising in the context of the γ-lasing problem.     

Steady-state motion of silicon islands driven by a DC current

The understanding and control of structures at the surface of crystals is a fashionable topic nowadays. The role of an electric heating current in shaping the morphology of vicinal (111) and (001) silicon surfaces during sublimation in ultra-high vacuum is well known. Less known is the behaviour of surface features when the crystal is in contact with its own saturated vapour, and thus at equilibrium. We report here the observation by reflection electron microscopy of two-dimensional, micrometre-sized silicon islands on a resistively heated Si(001) substrate held at equilibrium (vanishing super- and undersaturation) at temperatures between 1000 and 1100°C. Surprisingly, the islands are seen to perform a gliding motion at a constant velocity in or against the current direction, depending on the island reconstruction. The value of the velocity is, on the contrary, independent of island reconstruction and size. A simple model based on adatom electromigration is discussed, that allows us to account for all observed features.     

Brownian motion of spiral waves driven by spatiotemporal structured noise

Spiral chemical waves subjected to a spatiotemporal random excitability are experimentally and numerically investigated in relation to the light-sensitive Belousov-Zhabotinsky reaction. Brownian motion is identified and characterized by an effective diffusion coefficient which shows a rather complex dependence on the time and length scales of the noise relative to those of the spiral. A kinematically based model is proposed whose results are in good qualitative agreement with experiments and numerics.     

Scaling and decay in periodically driven scattering systems

We investigate irregular scattering in a periodically driven Hamiltonian system of one degree of freedom. The potential is asymptotically attracting, so there exist parabolically escaping scattering orbits, i.e. orbits with asymptotic energy E(out)=0. The scattering functions (i.e. the asymptotic out-variables as functions of an asymptotic in-variable) show a characteristic algebraic scaling in the vicinity of these orbits. This behavior is explained by asymptotic properties of the interaction. As a consequence, the number N(Deltat) of temporarily bound particles decays algebraically with the delay time Deltat, although no KAM scenario can be found in phase space. On the other hand, we find the number N(n) of temporarily bound particles to decay exponentially with the number n of zeros of x(t).     

Collisional decay of a strongly driven Bose-Einstein condensate

We study the collisional decay of a strongly driven Bose-Einstein condensate oscillating between two momentum modes. The resulting products of the decay are found to strongly deviate from the usual s-wave halo. Using a stochastically seeded classical field method we simulate the collisional manifold. These results are also explained by a model of colliding Bloch states.     

Pions in nuclear interior — sensitive test by hypernuclear decay

The effect of the pion wave distortion on the pi-mesonic weak decay ofΛ-hyperon in hypernuclei is studied by using two different pion optical potentials, one by Gmitro, Kamalov and Mach, which is given in momentum space, and the other by MSU group, which is in the standard Kisslinger form. The two potentials lead to a striking difference in the pi-mesonic decay, reflecting different behaviors of the pion wavefunctions deep inside the nucleus.     

On the separation of electronic and nuclear motion for molecules in an intense electromagnetic wave

The separation of electronic and nuclear variables is considered for a molecule in an intense electromagnetic field with frequency ω close to some electronic transition frequency. In this case the electron potential curves are essentially modified and a new branch of the vibrational spectrum can appear which has no counterpart in the original spectrum.     

润湿性梯度驱动液滴运动的格子Boltzmann模拟

运用考虑了固体与液体间分子作用力的格子Boltzmann方法,数值研究了由于固液界面上表面张力梯度引起的Marangoni效应驱动的液滴运动.当表面张力梯度较小时,计算结果和前人的理论预测符合较好.而表面张力梯度较大时,由于液滴不变形和准平衡态等假设不再满足,理论预测的液滴运动速度高于数值模拟的结果.计算结果显示,在向亲水端运动过程中液滴内部出现旋涡结构,当润湿性梯度较大时,其前进速度和接触角随时间变化出现振荡.     

Direct imaging of stochastic domain-wall motion driven by nanosecond current pulses

Magnetic transmission x-ray microscopy is used to directly visualize the influence of a spin-polarized current on domain walls in curved permalloy wires. Pulses of nanosecond duration and of high current density up to 1.0x10(12) A/m(2) are used to move and to deform the domain wall. The current pulse drives the wall either undisturbed, i.e., as composite particle through the wire, or causes structural changes of the magnetization. Repetitive pulse measurements reveal the stochastic nature of current-induced domain-wall motion.