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.     

Acceleration of heavy multicharged ions up to 1 MeV from a cleaned solid target irradiated by a femtosecond laser pulse with an intensity of 10<Superscript>16</Superscript> W/cm<Superscript>2</Superscript>

A noticeable increase in the charge and energy of ions accelerated from a solid tungsten target irradiated by a femtosecond laser pulse with an intensity higher than 10¹⁶W/cm² has been found when the target surface is precleaned by a nanosecond laser pulse with an energy density of 3 J/cm². Tungsten ions with charges up to +29 and energies up to 1 MeV were detected in this case, while the charge and energy of tungsten ions from a target with an uncleaned surface do not exceed +3 and 12 keV, respectively.     

Molecular effect in the formation of the energy spectrum upon the transmission of low-energy hydrogen ions through ultrathin carbon foils

The energy spectra of ions transmitted through ultrathin diamond-like foils irradiated by H⁺, H⁺₂, and H⁺₃ ions with energies from 2 to 12 keV/nucleon are studied. For molecular ions incident on the target with identical velocities, a considerable broadening of the energy spectrum is observed with an increase in the ion mass. The spectrum halfwidth reduced to the identical particle velocity remains constant for each type of incident ion, irrespective of the foil thickness.     

Elektronenausbeute bei Lithium-Ionenbeschuß von Bildwandlerflächen

The electron yield in the case of bombardment of a V2A type stainless steel plate by Li⁺ ions with energies between 20 and 80 keV was measured. The yield is increasing from 2·5 electrons per ion for 20keV to 4 for 70 keV. The electron yield in case of transmission by Li⁺ ions (number of electrons emitted on the back side of the foil per incident ion) of thin carbon foils with a layer of evaporated silver was measured. For this purpose the electrons emitted on the foil back side are accelerated in an immersion objective lens, and the resulting crossover of the beam is focussed into a Faraday cage by a projector lens. The electron yield depends on the ion energy and the foil thickness. Its value lies between 1 for a 1050 AU thick silver foil and 40 keV and 4 for a 380 AU thick silver foil and 80 keV. The range of Li⁺ ions in silver can be estimated by extrapolation of the yield curves. It is increasing from 600 AU for 10 keV to 2300 AU for 80 keV. The electron yield may not be characteristic for the target material since in a vacuum of 10^?4Torr the formation of a thin layer of polymerized hydrocarbon on the surface must be expected.     

kinetic energy reflection from polycrystals bombarded with Ar+, Kr+, and Xe+ ions

When the surface of a solid is bombarded with ions a fraction of the primary energy is reemitted by ion reflection and sputtering. The contribution of ion reflection or sputtering to energy reflection is determined by the mass ratio of the bombarding ions to the target atoms.^1,2 In the case of light ions the contribution of reflected ions is dominant. Results for He⁺ and Ne⁺ bombardment were described in a previous paper.³ The present paper deals with results for Ar⁺, Kr⁺, and Xe⁺ bombardment of the same targets as investigated before.³ The energies of the mass selected bombarding ions range from 9 to 16 keV. The measurements were carried out by means of the thermic detector described in a separate paper.⁴ For the given mass ratios most of the reemitted energy is related to sputtering.     

Electron Transitions during the Capture of an Electron by a He<Superscript>2+</Superscript> Ion at the Argon Atom

We have measured the absolute values of the total cross section of the one-electron capture by He²⁺ ions in the kinetic energy range 2–30 keV at the Ar atoms. The absolute values of the differential scattering cross sections of He⁺ ions formed during the one-electron capture and the electron capture with ionization at energies of 2.2, 5.4, and 30 keV have been determined. The electronic states of the formed ions have been determined using collision spectroscopy based on analysis of the change in the kinetic energy of He⁺ after the interaction. We have measured doubly differential (with respect to the kinetic energy and the scattering angle) cross sections of the formation of free electrons. The free electron formation channels (direct ionization and electron capture with ionization) have been analyzed by calculating the electron terms of the (HeAr)²⁺ system. The calculated cross section of capture with ionization is in conformity with the cross section measured using collision spectroscopy.     

A comparison of semi-local and non-local pseudo-potential techniques: calculations on Fe and FeH+

A new parameterization scheme is proposed for valence electron calculations which employ the pseudopotential formalism. This scheme has been implemented in calculations for Fe, Fe⁺, Fe²⁺, Fe³⁺ and FeH⁺. In comparison with conventional all-electron calculations the errors are of the order of 1 per cent in valence orbital energies, 0·5 per cent in ionization energies and 2 per cent in the molecular binding energy. Detailed comparisons are made between the present method, which is formulated in terms of orbital projection operators, and recent calculations based on local, angular momentum dependent, effective potentials. The two approaches are found to be capable of almost equal accuracy.     

Molecular effects in ion-induced secondary electron spectra

The energy spectra of slow secondary electrons from a copper surface under bombardment with H⁺, H⁺₂, and H⁺₃ ions have been measured at an energy of 200 keV/atom. Distinct molecular effects are revealed in the ratios of the respective distribution curves for molecular ion and proton impact.     

Study of the gamma emission from the 31-yr isomer of 178Hf induced by x-ray irradiation

A sample containing 6.3×10¹⁴ nuclei of the 16⁺ isomer of ¹⁷⁸Hf having a half-life of 31 yr and an excitation energy of 2.446 MeV was irradiated with x-ray pulses from a device operated at 15 mA to produce bremsstrahlung with an endpoint energy of 90 keV. The gamma spectra of the isomeric target were taken with a Ge detector. The intensity of the 325.5-keV (6⁺ → 4⁺) transition in the ground-state band of ¹⁷⁸Hf was found to increase by about 2%. Such an enhanced decay of the ¹⁷⁸Hf isomer is consistent with an integrated cross section value of 3×10^?23 cm² keV if resonance absorption occurs within energy ranges corresponding to the maxima of the x-ray flux, either near 20 keV or at the energies of the characteristic emission lines of W.     

Detachment of electrons during the collision of two negative ions

The cross sections of the detachment of one and two electrons during the collision of two negative ions H^? + H^?, H^? + Cs^?, and Cs^? + Cs^? are calculated in a wide range of collision energies: from the energy threshold to approximately 100 keV. In adiabatically slow collisions, the detachment of electrons occurs as a result of one-or two-electron Auger decays whose rates are calculated in the approximation of asymptotically large separations between ions. For high collision energies, the cross sections of the electron detachment are calculated by the method of close coupling of states. The calculated cross sections are in good agreement with the results of experimental measurements made for the H^? + H^? collision.     

Effect of bombardment with iron ions on the evolution of helium,hydrogen, and deuterium blisters in silicon

The effect of bombardment with iron ions on the evolution of gas porosity in silicon single crystals has been studied. Gas porosity has been produced by implantation hydrogen, deuterium, and helium ions with energies of 17, 12.5, and 20 keV, respectively, in identical doses of 1 × 10¹⁷ cm^–2 at room temperature. For such energy of bombarding ions, the ion doping profiles have been formed at the same distance from the irradiated surface of the sample. Then, the samples have been bombarded with iron Fe¹⁰⁺ ions with energy of 150 keV in a dose of 5.9 × 10¹⁴ cm^–2. Then 30-min isochoric annealing has been carried out with an interval of 50°C in the temperature range of 250–900°C. The samples have been analyzed using optical and electron microscopes. An extremely strong synergetic effect of sequential bombardment of silicon single crystals with gas ions and iron ions at room temperature on the nucleation and growth of gas porosity during postradiation annealing has been observed. For example, it has been shown that the amorphous layer formed in silicon by additional bombardment with iron ions stimulates the evolution of helium blisters, slightly retards the evolution of hydrogen blisters, and completely suppresses the evolution of deuterium blisters. The results of experiments do not provide an adequate explanation of the reason for this difference; additional targeted experiments are required.     

Secondary ion and Auger electron emissions from Ar+-ion-sputtered FeAl alloys

Some FeAl alloys, and pure Al and Fe samples, are sputtered in ultrahigh vacuum with Ar⁺ ions between 4 and 15 keV. As previously observed with CuAl alloys, the intensity of the principal Al Auger peak at 63.5 eV is a parabolic function of the Al concentration. Symmetric collisions Al → Al are thus much more efficient for Auger emission from pure aluminium than asymmetric collisions Ar → Al, the proportion of which among effective collisions hardly reaches 20% at 15 keV. Whatever the initial ion energy, the intensities of singly charged atomic secondary ions Al⁺ and Fe⁺, normalized to pure metals, are equal to the atomic concentration of the corresponding elements, whereas the normalized intensities of the multiply charged ions Al²⁺ and Al³⁺ are roughly equal to the square of Al concentration. These results agree with the occurence of two mechanisms in intrinsic ion emission: an electronic excitation process during the separation of the outgoing particle from the target (singly charged ions) and a collisional process from the symmetric collisions Al → Al only, with multiple Auger de-excitation outside the target (multicharged ions of light elements).     

Low-energy nuclear reactions in crystal structures

Results of studying low-energy nuclear reactions at the HELIS facility (LPI) are presented. Investigations of yields from DD reactions in deuterated crystal structures at deuteron energies of 10 to 25 keV show a considerable enhancement effect. It is shown that exposure of the deuterated targets to the Н⁺ (proton) and Ne⁺ beams with energies from 10 to 25 keV and an X-ray beam with the energy of 20 to 30 keV stimulates DD reaction yields. For the CVD diamond target, it is shown that its orientation with respect to the deuteron beam affects the neutron yield. The D⁺ beam is shown to cause much higher heat release in the TiD_x target than the Н⁺ and Ne⁺ beams, and this heat release depends on the deuterium concentration in the target and the current density of the deuteron beam.     

Stoßdissoziation von H 2 + - und D 2 + -Ionen

The angular and energy distribution of protons produced by collision-induced dissociations of H ₂ ⁺ ions with energies of 10 and 20 keV were measured in a parabola spectrograph. From these measurements the velocity distribution of the protons in the center of mass system of the H ₂ ⁺ ion can be calculated. This gives information about the type, the abundance, and the anisotropy of the processes involved. The most frequent transitions leading to dissociations are the excitation of the 2pσ_u state, the ionisation of the H ₂ ⁺ ion, the transition into the vibrational continuum, and the electron capture into the 1³ σ _u ⁺ state of the hydrogen. It is shown that the cross section for an electronic transition depends on the velocity of the ion, the distance of the nuclei in the ion, the angle between the internuclear axis and the direction of the primary ion beam, and the excitation energy of the target. The fraction of protons produced by vibrational excitation increases with increasing atomic number of the target. Concerning electronic transitions D ₂ ⁺ ions equal H ₂ ⁺ ions of the same velocity.     

A note on the radiative energy loss from an ion-bombarded surface

It has recently been argued that the heat radiation from spikes, according to the Stefan-Boltzmann law, plays an important role in thermal behaviour of a copper target bombarded with 100keV Xe⁺ ions. In this work we have monitored the temperature evolution of a copper bar subjected to a 40 keV N⁺, Xe⁺, Sb₂ ⁺, and a 20 keV Sb⁺ ion bombardment. Our measurements have not revealed any substantial differences between light and heavy ion bombardment as well as between atomic and molecular implantation. Those results are in agreement with the time constant for radiation being long, of order 10⁻⁶s. They also agree with the calculations of the radiative energy loss from the spike, based upon both cylindrical and spherical spike models. In all reported cases, the energy lost from the spike via the heat radiation, although much different for different projectiles, is smaller than 1% of the ion deposited energy and its influence on the target temperature evolution lies within uncertainty of a typical ion current measurement. This work was carried out as a part of Research Project CPBP 01.09     

Levels in 156Gd studied in the (n, γ) reaction

Levels up to 2.3 MeV in ¹⁵⁶Gd have been studied using the (n, γ) reaction. Energies and intensities of low-energy γ-rays and electrons emitted after thermal neutron capture have been measured with a curved-crystal spectrometer, Ge(Li) detectors and a magnetic electron spectrometer. High-energy (primary) γ-rays and electrons have been measured with Ge(Li) detectors and a magnetic spectrometer. The high-energy γ-ray spectrum has also been measured in thermal neutron capture in 2 keV resonance neutron capture. The neutron separation energy in ¹⁵⁶Gd was measured as S_n = 8535.8 ± 0.5 keV.About 600 transitions were observed of which ~50% could be placed in a level scheme containing more than 50 levels up to 2.3 MeV excitation energy. 42 of these levels were grouped into 15 excited bands. In addition to the β-band at 1050 keV we observe 0⁺ bands at 1168, 1715 and 1851 keV. Other positive-parity bands are: 1⁺ bands at 1966, 2027 and 2187 keV; 2⁺ bands at 1154 (γ-band) and 1828 keV; and 4⁺ bands at 1511 and 1861 keV. Negative-parity bands are observed at 1243 keV (1^?), 1366 keV (0^?), 1780 keV (2^?) and 2045 keV (4^?). Reduced E2 and E0 transition probabilities have been derived for many transitions. The ground band, the β- and γ-bands and the 0⁺ band at 1168 keV have been included in a phenomenological four-band mixing calculation, which reproduces well the experimental energies and E2 transition probabilities.The lowest three negative-parity (octupole) bands of which the 0^? and the 1^? bands are very strongly mixed, were included in a Coriolis-coupling analysis, which reproduces well the observed energies. The E1 transition probabilities to the ground band are also well reproduced, while those from the higher-lying 0⁺ bands to the octupole bands are not reproduced. Absolute and relative transition probabilities have been compared with predictions of the IBA model and the pairingplus-quadrupole model. Both models reproduce well the E2 transitions from the γ-band, while strong disagreements are found for the E2 transitions from the β-band. The IBA model predicts part of the decay features of the higher lying 2⁺₂, 4⁺₁ and 2^?₁ bands.     

The interaction of fast H 3 + ions with a clean Ni-surface

Scattering of H ₃ ⁺ ions from a clean Ni(111) surface is observed at energies below 1 keV and grazing incidence in a time-of-flight system. The interaction with the surface leads to neutral particles mainly which are identified from the energy distributions as H and H₂. The neutralisation/dissociation mechanism is probably a resonant charge transfer of Ni electrons into the non-binding ground state of H₃.     

Cold electrons acceleration in TNSA laser-generated plasma using a low-contrast fs laser

The fs laser facility in Bordeaux, delivering an intensity of 10¹⁸ W/cm² at normal incidence on thin foils, has been used to induce forward electron and ion acceleration in target-normal-sheath-acceleration (TNSA) regime. Micrometric thin foils with different composition, thickness, and electron density, were prepared to promote the charge particle acceleration in the forward direction. The plasma electron and ion emission monitoring were performed on-line using SiC semiconductor detectors in time-of-flight (TOF) configuration and gaf-chromics films both covered by thin absorber filters. The experiment has permitted to accelerate electrons and protons. A special attention was placed to detect relativistic hot electrons escaping from the plasma and cold electrons returning to the target position. The electron energies of the order of 100 keV and of about 1 keV were detected as representative of hot and cold electrons, respectively. A high cold electron contribution was measured using low-contrast fs laser, while it is less evident using high-contrast fs lasers. The charge particle acceleration depends on the laser parameters, irradiation conditions, and target properties, as will be presented and discussed.     

Energy and charge distributions of fast hydrogen ions and atoms reflected from Cu in the case of grazing incidence

The energy and charge distributions of protons and hydrogen atoms reflected from the Cu surface in the case of grazing incidence angles are measured at energies of incident particles (H⁺ and H⁰) of 200 and 250 keV. The charged fractions of reflected particles are analyzed. A weak dependence of the neutral fraction of reflected particles on the scattering angle is discovered for incidence angles of 1°–2° and an energy of scattered particles of 60 keV or less. It is shown that the neutral fraction of reflected particles with an energy of 60–80 keV or more is independent of the scattering angle and is determined by the ratio of the cross sections for the electron capture and loss by ions in the material.     

Photoluminescence and structural defects in silicon layers implanted by iron ions

The photoluminescence spectra of silicon samples implanted by ⁵⁶Fe⁺ ions [energy, 170 keV; dose, 1×10¹⁶, (2–4)×10¹⁷ cm^?2] and annealed at temperatures of 800, 900, and 1000°C are measured. The structure of the samples at each stage of treatment is investigated using transmission electron microscopy (TEM). It is found that the phase formation and morphology of crystalline iron disilicide precipitates depend on the dose of iron ions and the annealing temperature. A comparison of the dependences of the intensity and spectral distribution of the photoluminescence on the measurement temperature, annealing temperature, and morphology of the FeSi₂ phase revealed the dislocation nature of photoluminescence.