Many-body effects in the formation of multiply charged ions in a strong laser field

Some of the many-body effects in the formation of multiply charged ions in a laser field have been taken into account: inelastic tunneling, collective tunneling, and magnetic moment projection relaxation of the atomic core. Strong fields with an intensity exceeding 10¹⁷ W cm⁻² are considered when the magnetic component of the laser field acts on the free motion of a photoelectron; therefore, the formation of multiply charged ions through rescattering becomes unlikely. Numerical calculations have been performed for Ar⁹⁺ … Ar¹³⁺, Kr¹⁹⁺ … Kr²³⁺, Rb¹⁰⁺, and Rb¹¹⁺ ions. A significant contribution of collective tunneling, which was not observed in weaker fields investigated previously, has been revealed. Allowance for collective tunneling is shown to reduce the intensity leading to saturation by more than 10%. In this case, the yield of multiply charged Rb ions changes by an order of magnitude, while the yield of multiply charged Ar and Kr ions changes by more than a factor of 2. Comparison with experimental data on the formation of argon ions under the action of a linearly polarized laser pulse is made.     

Simplified classification of atmospheric charged particles

One of the most important problems on the atmospheric studies is electrostatic interaction between atmospheric cluster ions and aerosol particles.Atmospheric ions are currently classified into 5 overlapping categories having mobilities ranging from 1.3 cm² V^?1 s^?1 to less than 0.004 cm² V^?1 s^?1.We have considered charged ultrafine aerosols and cluster ions as charged atmospheric particles. This classification can be used in the interpretation of electrostatic interactions among these particles.Attachment processes between ultrafine aerosols can be considered as recombination processes between charged atmospheric particles. Atmospheric particles are grouped into two categories, but the number of recombination and attachment coefficients is not reduced.     

Singly charged tungsten and tantalum ions observed during high-temperature field evaporation

High-temperature field evaporation of tungsten and tantalum emitters in the temperature range from room temperature to 2500 K is studied using a static magnetic mass spectrometer equipped with a field source of ions. At room temperature, triply charged W³⁺ and Ta³⁺ ions alone are observed in the mass spectra. However, as the emitter temperature grows, the charge of the ions decreases. At T ≈ 1000 K, doubly charged W²⁺ and Ta²⁺ ions dominate in the spectra, and singly charged W⁺ and Ta⁺ ions appear in the temperature range 1900 < T < 2500 K. The evaporation rate of the singly charged ions is one to two orders of magnitude lower than the evaporation rate of the doubly charged particles. The energy parameters of field evaporation for differently charged tungsten ions are found.     

Ellipticity-dependent of multiple ionisation methyl iodide cluster using 532 nm nanosecond laser

The dependence of multiply charged ions on laser ellipticity in methyl iodide clusters with 532 nm nanosecond laser was measured using a time-of-flight mass spectrometer. The intensities of multiply charged ions I^q+(q = 2–4) with circularly polarised laser pulse were clearly higher than those with linearly polarised laser pulse but the intensity of single charged ions I⁺ was inverse. And the dependences of ions on the optical polarisation state were investigated and a flower petal and square distribution for single charged ions (I⁺, C⁺) and multiply charged ions (I²⁺, I³⁺, I⁴⁺, C²⁺) were observed, respectively. A theoretical calculation was also proposed to simulate the distributions of ions and theoretical results fitted well with the experimental ones. It indicated that the high multiphoton ionisation probability in the initial stage would result in the disintegration of big clusters into small ones and suppress the production of multiply charged ions.     

Simulating the stopping dynamics of highly charged ions in an ultra-cold, strongly coupled plasma

We introduce a method for stopping highly charged ions (HCIs) in a laser-cooled one-component plasma (OCP) of ²⁴Mg⁺ ions and present results on stopping times derived from realistic molecular dynamics simulations of the complete stopping process. This stopping scheme can provide ultra-cold highly charged ions for future in-trap precision mass measurements. The choice of an ultra-cold ion plasma as a stopping medium is governed by the almost negligible charge exchange of the HCI with the laser-cooled ions and the very low temperatures which can be reached. In our analysis we focus on the stability and fast recooling of the plasma – two features essential for the experimental realization of this stopping scheme.      

Mechanism of charging of the pyrite/aqueous interface as deduced from the surface potential measurements

Surface potential of pyrite in an aqueous environment was measured by means of a single crystal pyrite electrode. The effect of the activity of S²⁻ and Fe²⁺ ions as well as of pH, was examined. The results show that S²⁻ and Fe²⁺ ions are the dominant potential determining ions. These ions are bound to surface sites with the extent depending on their activity in the bulk of the solution. Adsorption affinity of S²⁻ ions is significantly higher than that of Fe²⁺ ions so that in most cases the pyrite surface is negatively charged. The results were explained on the basis of the surface complexation model. It was found that the surface potential depends also on pH.     

纳秒强激光中丙酮团簇增强的多价电离现象

利用脉宽为25 ns的脉冲Nd: YAG 532 nm的激光，在10¹⁰—10¹¹ W/cm²的强度下，用飞行时间质谱对丙酮团簇的激光电离过程进行了研究. 观察到了较强的O^q+(q=2—4)和C^q+(q=1—4)高价离子信号，这些高价离子 C⁴⁺，C³⁺，C²⁺，O⁴⁺，O³⁺，O²⁺的最大概然平动能分别为240 eV，70 eV，30 eV，90 eV，80 eV，40 eV. 高价离子的强度和平动能随激光强度的增大而增大. 我们提出一个多光子电离引发，逆韧致吸收加热-电子碰撞电离模型来解释高价离子的产生. 关键词： 丙酮 团簇 库仑爆炸 高价离子     

High-accuracy mass measurements in ion traps and storage rings

High-accuracy mass measurements have recently been performed on radioactive isotopes produced by proton-induced spallation at the on-line isotope separator ISOLDE at CERN and by heavy-ion projectile fragmentation at the fragment separator FRS at GSI. At ISOLDE, singly charged ions were injected into the Penning trap mass spectrometer ISOLTRAP and their masses determined by observing their cyclotron frequencies in the homogeneous magnetic field of the ion trap. At GSI, bare, hydrogen, or helium-like ions were injected into the experimental storage ring ESR, electron-cooled to the same velocity, and their masses determined by observing their revolution frequencies in the ESR. With ISOLTRAP and ESR, resolving power in the range of 4 × 10⁵< = m/Δ m(FWHM)< = 10⁷ and an accuracy up to \delta m/m~ 10^-7 were achieved for radioactive isotopes. Mass measurements of highly charged ions of stable isotopes were performed at Stockholm by use of SMILETRAP. In this case, a resolving power of about 10⁸ and an accuracy close to 10^-9 were obtained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Branching ratios of successive emission (up to three) of C2n + (n = 1–5) fragments in asymmetrical fission processes of C60 r+ ions (r = 4–6)

Highly charged C₆₀ molecules are produced in collisions between neutral C₆₀ and multiply charged ions within a large range of temperatures. Successive emission of one, two or three light monocharged fragments referred as one-, two- and three-step processes have been observed. The experimental mass branching ratios for the emission of one C_2n⁺ fragment from C₆₀⁶⁺, C₆₀⁵⁺ and C₆₀⁴⁺ ions are compared with the theoretical values using a statistical model. From hotter C₆₀⁶⁺ ions, branching ratios for three-step processes have been measured and the data are in good agreement with an estimation using the branching ratios in one-step process.     

Dissociation of alkane ionized molecules

The subject of investigation is the fragmentation of variously charged molecular ions arising in col-lisions of several kiloelectronvolt H⁺, He²⁺, and Ar⁶⁺ ions with molecules of the simplest alkanes (from methane to butane). Using the method of time-of-flight mass spectrometry, the formation cross sections of dissociation-induced fragment ions are measured. The dissociation takes place when an incident ion captures an electron from a methane, ethane, or propane molecule. The role of additional ionization of the molecule, which accompanies the electron capture by the incident ion, is elucidated. The kinetic energy spectrum for protons resulting from the fragmentation of multiply charged alkane ions is determined. The most plausible kinetic energies of protons depending on the degree of ionization and molecule size fall into the range 1–25 eV. It is shown that, when the molecule loses several electrons, the kinetic energies of protons are governed by Coulomb interaction between all fragment ions and are determined by their flying apart from the relative spatial arrangement of corresponding atoms in a parent molecule.     

SMILETRAP — Atomic mass measurements with ppb accuracy by using highly charged ions

In the SMILETRAP facility externally produced highly charged ions are captured in a Penning trap and utilized for high precision measurements of atomic masses. Accuracy tests on a ppb level have been performed, using highly charged carbon, oxygen and neon ions. In all cases hydrogen ions served as a reference for the calibration and monitoring of the magnetic field in the trap. Deviations smaller than 3 ppb from the expected results were found in mass measurements of the¹⁶O and²⁰Ne atomic masses. The proton atomic mass, determined from the reference measurements on hydrogen ions, is in good agreement with the accepted value [1]. A direct mass measurement on the⁸⁶Kr-isotope, using trapped⁸⁶Kr²⁹⁺-ions is reported.     

Neutralization of H− ions in collisions with fast, multiply charged ions

The neutralization of H⁻ ions in collisions with fast, multiply charged ions is considered in the parameter region where the Born approximation applies. An analytical formula is obtained for the H⁻ neutralization cross section in such collisions. Zh. Tekh. Fiz. 69, 1–4 (July 1999)     

Comparison of detection efficiencies of negatively charged gold-alkanethiolate-, gold-sulfur- and gold-clusters in ToF-SIMS

In order to improve quantification of high mass ions, the influence of cluster composition on detection efficiencies has been studied using a TOF-SIMS IV with the extended capability of postaccelerating ions up to 20 keV. In this experimental study, we focus on the comparison of detection efficiencies for three types of negatively charged secondary cluster ions: gold-alkanethiolate-clusters (Au_xM_y), gold-sulfur-clusters (Au_xS_y) and gold-clusters (Au_x). The clusters were sputtered from self-assembled monolayers of hexadecanethiols on gold substrates using 10 keV Ar⁺ primary ions. The detection efficiencies were derived on the basis of a function for the secondary electron yield and a fourth-order approximated Poisson probability distribution for electron propagation and amplification within the microchannel plate.In addition to the well-known dependence of detection efficiencies on ion mass and energy, which has already been studied for positively charged ions, we were able to show a similar behaviour for the investigated negatively charged secondary ions. We have observed major variations among the three types of clusters at similar mass and energy as predicted in a theoretical approach. The observed differences are due to the different composition of the investigated clusters which has a major influence on the kinetic ion induced electron emission within the microchannel plate. For the first time it was possible to experimentally verify these predictions for detection efficiencies.     

Parity Nonconserving (PNC) Electroweak Radiative Corrections for Highly Charged Ions (HCI)

We derive the electroweak radiative corrections to the basic PNC atomic transition amplitude for highly charged hydrogenlike ions. In the case of highly charged ions (HCI) effects of strong fields are reflected by the momentum transfer q ² involved. It is of the order q ²≈m _e ² inHCI, while q ²≈0 inneutral atoms. This may open the possibility to search for “new physics” beyond the Standard Model and to test the Standard Model in experiments with HCI. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the energy dependence of the yield of doubly charged negative ions during the capture of free electrons by C60(CF3)12 trifluoromethylfullerene molecules

Peaks of C₆₀(CF₃) _n ^2? doubly charged negative ions (n = 6–12) have been observed in the mass spectra of the resonance electron capture by trifluoromethylfullerene C₆₀(CF₃)₁₂ molecules. It has been established that these ions are formed owing to the attachment of two free isoenergetic electrons. The autodetachment of an extra electron has been detected for the doubly charged molecular ions (n = 12). It has been established from the observation of the delayed fragmentation of the most abundant ions with n = 8 and 10 that the doubly charged negative ions, like their singly charged analogs, are metastable with respect to the separation of the CF₃ fragment(s). The yield of doubly charged negative ions has been obtained as a function of the electron energy. By comparing them with the analogous dependences for the singly charged ions, the specific features have been revealed which were associated with the presence of the repulsive Coulomb barrier and the regular effect of the doubled energy of two additional electrons on the energy dependence of the dissociative decay of the doubly charged negative ions. The absolute cross section for the formation of the C₆₀(CF₃) ₁₀ ^2? ions has been measured. At the energy of their yield maximum near the 5 eV, it is ～1 × 10^?19 cm².     

Effect of hydroxyl and oxygen ions on optical stability of F-centers in KBr crystals

The effect of the anionic impurities OH^–, O ₂ ^§- , and O^2– on the optical stability of F-centers in KBr crystals was investigated. It is shown that the stability of F-centers is independent of the presence of hydroxyl ions (OH^–) and molecular oxygen ions (O ₂ ^– ) in the crystal lattice. It is suggested that the low stability of F-centers in KBr-KOH crystals is due to doubly charged oxygen ions.Translated from Izvestiya Vysshikh Uchebnykh Zavendenii, Fizika, No. 10, pp. 107–112, October, 1972.     

K-line X-ray fluorescence from highly charged iron ions under dense astrophysical plasma conditions

In the present work, we report an investigation of plasma environment effects on the atomic parameters associated with the K-vacancy states in highly charged iron ions within the astrophysical context of accretion disks around black holes. More particularly, the sensitivity of K-line X-ray fluorescence parameters (wavelengths, radiative transition probabilities, and Auger rates) in Fe XVII–Fe XXV ions has been estimated for plasma conditions characterized by an electron temperature ranging from 10⁵ to 10⁷ K and an electron density ranging from 10¹⁸ to 10²² cm⁻³. In order to do this, relativistic multiconfiguration Dirac-Fock atomic structure calculations have been carried out by considering a time averaged Debye-Hückel potential for both the electron–nucleus and electron–electron interactions.     

Spectroscopy using stimulated electron–ion recombination

Spectroscopic results obtained on multiply charged few electron ions by using laser stimulated two-step recombination in ion storage rings are presented in an overview. Line splittings in transitions between Rydberg levels were observed for helium like and beryllium like ions. Emphasis is given to results on the beryllium like system N³⁺ where information about the splitting between high angular momentum levels (l⩾4) was obtained for the Rydberg levels n=13 and 8 with experimental errors of about ±0.02 meV. This revised version was published online in August 2006 with corrections to the Cover Date.     

Elementary processes during collisions of ions with tryptophan molecules

The relative cross sections of elementary processes occurring in single collisions of tryptophan molecules in the gaseous phase with He²⁺ ions with energy 4 keV/u are measured using time-of-flight mass spectrometry for studying the mechanism of radiation damage of amino acid molecules. The fragmentation channels for intermediate singly and doubly charged tryptophan molecular ions formed during one-electron capture, two-electron capture, and electron capture with ionization are investigated. Significant difference is observed in the mass spectra of fragmentation of intermediate doubly charged ions formed during the capture with ionization and double capture, which is associated with different energies of excitation of {C₁₁H₁₂N₂O₂}²⁺* ions.     

Secondary doses delivered to an anthropomorphic male phantom under prostate irradiation with proton and carbon ion beams

Secondary radiation exposure of patients undergoing radiation therapy with light ions is of great concern due to possible tissue damage and risk of induction of secondary cancers.Secondary particles such as neutrons, protons and heavier ions are produced when the primary ions interact through nuclear inelastic reactions with the beam-line components, and with the tissues of the patient.Evaluations of secondary doses delivered to an anthropomorphic male phantom under prostate irradiation with ¹H and ¹²C ion beams with energies 172 MeV and 330 MeV/u, respectively, have been performed with the Monte Carlo code SHIELD-HIT.Fluences of secondary particles with atomic mass A = 1–7 and energies up to 200–600 MeV/u are observed in organs even at larger distances (40–50 cm) from the irradiated volume. The secondary absorbed doses in selected organs are discussed taking into account the dose contribution from secondary neutrons, and the contribution from charged fragments that are not the products of neutron interactions. For ¹²C ion irradiation, a substantial contribution to the absorbed organ dose is due to charged fragments. This contribution decreases from 81% in the organs close to the irradiated volume to 35–40% in the organs at larger distances.