Spectral shape of the 2E1 decay from 2s state in He-like tin

The two-photon 2E1 transition from the singlet 2s state of heliumlike tin was measured. An alternative experimental approach was adopted in the present investigation where the two-photon emission results from the decay of the 2s state by selective K-shell ionization of Li-like tin ions in relativistic collisions with a low-Z gaseous target, which allowed for a measurement of the undistorted two-photon spectral shape. The measured 2E1 energy distribution was compared with fully relativistic calculations, which predict a Z dependence of the distribution. The preliminary results indicate the best agreement with the relativistic many body calculations for tin, and thus confirm the sensitivity on Z. Detailed data analysis is still in progress.     

Double ionization of helium by relativistic highly charged ion impact

We consider an interesting realization of the fundamental four-body problem: double ionization of helium in superintense electromagnetic fields generated by highly charged ions in relativistic collisions. We show how the simultaneous interaction of such fields with all three target constituents (which is not described by first-order theory) strongly influences the collision dynamics even at very high collision energies and how a “genuine” photoemission-like pattern may emerge in collisions at extreme relativistic energies. A very good agreement with available experimental data is obtained.     

氦原子与非全裸氟离子碰撞过程中多重电离的研究

用飞行时间符合技术测量了１．５－７．５ＭｅＶ非全裸氟离子与氦原子碰撞引起的氦的双、单重电离相对截面比，对非全裸离子核外电子对碰撞过程的影响进行了讨论。对碰撞系统还进行了多体经典轨道蒙特－卡罗模拟，得到氦的双、单重电离绝对截面，并对结果进行了讨论     

Triple coincidence experiment to explore the two-electron continuum states of the projectile resulting from mutual ionization in 100-keV He0 + He collisions

The existence of the two-electron cusp in atomic collisions, i.e., the enhanced emission of two electrons in the forward direction with velocities equal to that of the projectile, has been investigated experimentally. Using a time-of-flight technique, the energies of the two electrons resulting from the simultaneous target and projectile ionization in 100-keV He(0)+He collisions have been measured by detecting triple coincidence between the electrons and the outgoing He(+) ion. The coincidence yield clearly shows a peak as a function of the electron energies at the expected cusp position. Furthermore, a strong correlation was found between the energies of the two electrons, which is traced back to an angular correlation of 180 degrees in the projectile-centered reference system.     

Hadron spectroscopy from B-factories

We review the recent experimental results on hadron spectroscopy from B-factories focusing on the exotic charmonium-like states. Among them we discuss the X(3872), Y(3940), Z(4430)+, Z(4050)+, Z(4250)+ and Y(4140) states found in B-meson decays, the X(3940) and X(4160) states produced in double charmonium production, the Y(4260), Y(4325), Y(4660) and X(4630) states produced with initial-state radiation in e+e-annihilation and the X(3915), Y(4350) states observed in two-photon collisions.     

Multi electron capture processes in slow collisions between X<Superscript>7+</Superscript> (X = N,O and Ne) ions with C<Subscript>60</Subscript>

Electron capture processes in collision between slow X⁷⁺ (X = N, O and Ne) ions and C₆₀ fullerene have been investigated using coincident measurements of the number n of ejected electrons, the mass and charge of the multicharged C₆₀ ^r+ recoil ions and their fragments C_m ⁱ⁺ and the final charge state of the outgoing projectiles X^(q-s)+ ( ). The collision velocity is about 0.4 a.u. The partial cross-sections σ_r ^s , corresponding to r electrons transferred to the projectile with only s electrons stabilized, have been measured. Cross-sections for collisions “inside” and those “outside” the C₆₀ cage have been separated by analyzing the kinetic energy of the outgoing projectile. The mean final charge state for frontal collisions has been measured to 3.1, 2.6 and 2.5 for N⁷⁺, O⁷⁺ and Ne⁷⁺ respectively. These results show the importance of the core effect on the stabilisation processes of captured electrons.     

Glow discharge in rare-gas and metal vapour mixture

Applying the Boltzmann equation to a He-Cd mixture discharge the electron energy distribution functions, kinetic coefficients and collision frequencies are numerically calculated. Calculations are made for a homogeneous and stationary discharge plasma subjected to an externally applied electric field. The collision processes which have been taken into account are elastic and inelastic collisions of electrons with He and Cd atoms as well as mutual encounters of electrons. In this case the electron energy distribution and all the quantities calculated from it are dependent on the reduced electric field, the ionization degree and the relative cadmium concentration.     

TWO TEMPERATURES EMISSION OF RELATIVISTIC α-PARTICLES IN HIGH-ENERGY HEAVY-ION COLLISIONS

We have performed an experimental study of the α-fragments emitted from collisions between emulsion nuclei and heavy-ion projectiles at beam energies beyond 1A GeV. It is shown that the transverse momentum distributions of relativistic α-particles give evidence for two effective temperatures emission in high-energy heavy-ion collisions. The data might take on a new signature for the phase transition from hadron matter to quark matter.     

Cq+ 和Oq+与原子碰撞的电子俘获过程的理论研究

在ECPSSR理论的基础上， 利用OBKN近似描述电子俘获过程， 得到了包括电子俘获过程贡献的ECPSSR理论， 编写了相应的计算程序。 采用该程序计算了不同电荷态离子与多种靶原子碰撞的电子俘获截面和相应的X 射线产生截面， 将计算得到的包含电子俘获过程贡献的X 射线产生截面与实验结果进行了比较。 对于具有满K壳层的入射离子碰撞， X 射线产生截面与入射离子电荷态基本无关； 对于以直接电离为主导的碰撞过程， 计算得到的X 射线产生截面与实验数据符合得很好； 对于全裸和单K空穴入射离子的碰撞， 计算高估了X 射线产生截面。 Based on the ECPSSR theory, the contribution of the electron capture is described by the OBKN theory. The cross sections of electron capture and X ray production for the collision of different charge state projectiles with various targets are calculated, and compared with the available experimental data. It is found that the obtained X ray production cross sections are almost independent of the projectile charge states for projectiles without a K vacancy. For the collision processes of direct ionization, the present calculated results agree well with the experimental data. The calculations overestimate the X ray production cross sections for the projectiles with full and a K vacancy.     

Cold atomic collisions: coherent control of penning and associative ionization

Coherent control techniques are computationally applied to cold (1 mK相似文献   

Theoretical determination of K X-ray transition energy and probability values for highly charged ions of lanthanum and cerium

The interaction between positronium and a helium atom is studied using the 5-body classical trajectory Monte Carlo method. We present the total cross sections for the dominant channels, namely for single ionization of the target, and ionization of the projectile, resulting from pure ionization and also from electron transfer (capture or loss) processes for 1–5.7 a.u. incident velocities of the positronium atom. Our results were compared with the calculated data using hydrogen projectiles having the same velocities as well as with the experimental data in collisions between H and He [R.D. DuBois, Á. Kövér, Phys. Rev. A 40, 3605 (1989)]. We analyze the similarities and deviations for ionization of helium atoms by positronium and hydrogen projectile impact.     

Rydberg-Rydberg collisions: resonant enhancement of state mixing and penning ionization

In rubidium Rydberg states, the collision nD_(5/2)+nD_(5/2)-->(n-2)F_(7/2)+(n+2)P_(3/2) is nearly resonant in the vicinity of n=43. As a result, over a short range of n centered around n approximately 43 the Rydberg-Rydberg interaction potential is quite large and turns from repulsive to attractive [Phys. Rev. A 75, 032712 (2007)10.1103/PhysRevA.75.032712]. We use state-selective field ionization to investigate the effect of this resonance on instantaneous excitation of mixed two-particle states, state-mixing collisions, and Penning ionization. We find that these processes depend on the magnitude and sign of the two-particle interaction potential, and thus on n near the resonance. The large magnitude of the observed state mixing provides evidence for many-body effects.     

Extracting Information About Few-Body Breakup Thresholds from High-Energy Collisions

We show that the analysis of high-energy collisions provides an alternative, and sometimes advantageous, method of gathering information on a breakup system at threshold. We demonstrate the applicability of this approach by extracting the s-wave scattering length a₀ for the collision of electrons by neutral atoms in metastable states from measurements of photo- and collisional detachment of electrons from negative ions and electron capture to continuum states of neutral projectiles in atomic ionization collisions. Finally, we discuss how to generalize these ideas to gather information about an N-body threshold behavior.Fax: +54 2944 445299, Phone: +54 2944 445234     

Dynamics of ionization mechanisms in relativistic collisions involving heavy and highly-charged ions

The dynamics of mechanisms associated with the ionization of inner-shell electrons in relativistic collisions involving heavy and highly-charged ions is investigated within a nonperturbative approach formulated explicitly in the time domain. The theoretical treatment is based on the exact numerical solution of the time dependent Dirac equation for two Coulomb centers on a lattice in momentum space. We present results for ionization in encounters between 100 MeV/u Au⁷⁹⁺ projectile ions impinging on a hydrogen-like uranium target. By directly visualizing the collision dynamics we identify a new ionization mechanism in which electrons are emitted from the internuclear region preferentially in the transverse direction with respect to the projectile trajectory. A striking characteristic of this ionization mechanism is that the velocity of the electron is higher than the projectile velocity. Received 26 June 2001 and Received in final form 27 November 2001     

强扰动区C~(q+)离子与He原子碰撞中有效电荷研究

本文利用经典过垒电离模型(Class Over Barrier Ionization)处理100-400ke V/amu强扰动区(q/v1)的不同价态非全裸离子Cq+(q=1-4)与全裸离子H1+,He2+,Li3+与He原子碰撞过程.发现相同价态下,全裸离子的双单电离截面比R21明显低于非全裸离子,原因在于两者的电子结构明显不同.非全裸离子的外壳层电子在碰撞过程中会有一定几率过垒,这在以往的研究中并未考虑.利用模型计算结果与实验数据的比对,估计入射离子第二有效电荷,最终确定入射离子在电离过程中的第一和第二有效电荷.     

852.3 nm激光线共振激发Cs蒸气的荧光光谱

研究了Cs蒸气被单模半导体激光器的852.3 nm线激发产生的荧光光谱。由Cs,Cs₂的荧光及其强度确定了在受激Cs-Cs₂系统中的若干碰撞和辐射过程。高位态原子线是由Cs(6P_3/2)+ Cs(6P_3/2)到Cs(6D,8S)的碰撞能量合并形成的,Cs₂(B 1∏_u)带则由Cs(6P)+Cs₂(X 1Σ+_g)碰撞转移产生。通过激发转移、能量碰撞合并和Cs₂-Cs碰撞传能研究了6 2P原子的精细结构混合,得到了6P_3/2→6P_1/2碰撞转移速率系数是(5.2±2.1)×10-11 cm3·s-1,给出了过程Cs₂(B 1∏_u)+Cs(6S)→Cs₂(X 1Σ+_g)+Cs(6P_1/2)的速率系数是(1.0±0.4)×10-9 cm3·s-1。     

Single electron capture in collisions of N^q＋ （q = 5, 6, 7） ions with helium

Close-coupling calculations are carried out for cross sections of the single electron capture in collisions of N^q+ (q = 5, 6, 7) ions with helium atoms in the collision velocity range from 0.3 a.u. to 1.8 a.u. The relative importances of the single ionization (SI) to the single capture (SC) are investigated for the N^q+ (q = 5, 6, 7) projectiles, respectively. The SI/SC cross section ratio for the N⁷⁺ projectile obtained from our calculations is in excellent agreement with the experimental data. The ratio curves also show us distinct behaviours when the charge of the projectile is different. The partial electron capture cross sections for different projectiles indicate that the electron on the target He atom tends to be captured by the projectile into its lower orbital of the outer shell with the decreasing projectile charge.     

Electromagnetic processes in relativistic heavy ion collisions

Electromagnetic effects in relativistic heavy ion collisions with impact parameter larger than the sum of the nuclear radii are studied using the virtual photon method. With increasing value of the relativistic parameter γ the hardness of the virtual photon spectrum increases. This leads to interesting new effects which will also have to be considered in the design of future relativistic heavy ion machines and experiments. The excitation of high-lying giant E1 and E2 multipole resonances is calculated as well as electromagnetic pion production. Coulomb bremsstrahlung is calculated and compared to the bremsstrahlung emitted in the more violent central nuclear collisions. K-shell ionization and electron-positron pair production is studied. The latter process has a very large cross section for heavy ions and contributes significantly to the stopping power of relativistic heavy ions in a dense medium.     

Ionization dynamics of helium dimers in fast collisions with He++

By employing the cold target recoil ion momentum spectroscopy technique, we have investigated the (He+, He+) breakup of a helium dimer (He2) caused by transfer ionization and double capture in collisions with alpha particles (E = 150 keV/u). Surprisingly, the results show a two-step process as well as a one-step process followed by electron exchange. In addition, interatomic Coulombic decay [L.?S. Cederbaum, J. Zobeley, and F. Tarantelli, Phys. Rev. Lett. 79, 4778 (1997).] is observed in an ion collision for the first time.