Specific features of the excitation spectrum of helium II in a plasma initiated by an electron beam

The emission of a low-pressure helium plasma (P≤2 Torr) initiated by a monochromatic electron beam is investigated. It is found that an increase in the current leads to a drastic increase in the rate of charge exchange of doubly charged helium ions. The assumption is made that inelastic collisions of He⁺⁺ ions with metastable helium atoms provide the main channel of charge exchange of these ions due to the reaction He⁺⁺+Hem→ He⁺*+He ₀ ⁺ .     

Radiative capture of deuterons in154Sm and238U

Angular — and velocity — distributions of electrons emitted near zero degree from projectile ions (H⁺, H ₂ ⁺ , H ₃ ⁺ , He⁺, He⁺⁺ at 1.7 MeV/u) traversing solid carbon foils (2 to 20) μg/cm²) have been measured. The data give clear evidence of production mechanisms which go beyond those reported elsewhere.     

Desorption of cluster ions from adsorbed methane under cryogenic condition by low-energy ion irradiation

We have investigated ion desorption from adsorbed methane following keV He⁺ ion irradiation. The thickness of the adsorbed layer was precisely controlled. For mono-layered methane, only monomer ions (CH_x⁺) were desorbed by 1 keV He⁺ ion irradiation. On the other hand, a large number of cluster ions (C_nH_x⁺) up to n = 20 were desorbed from multi-layered film. Among cluster ions, molecular ions with CC bonds were found, which indicates that chemical bonds are newly formed by ion irradiation. Based on the results for thickness dependences of the mass spectral patterns, it was elucidated that the monomer ions are desorbed from the top surface layer through single electron excitation. While the cluster ions are formed mainly in the inside of the layers along the nuclear track due to the high-density electronic excitation, which is produced by nuclear collision between incident He⁺ ions and frozen molecules.     

Oxidation state of Fe and Ti ions implanted in yttria-stabilized zirconia studied by XPS

The oxidation state of Fe and Ti ions implanted in yttria stabilized zirconia (YSZ) was studied by XPS (X-ray photoelectron spectroscopy) in combination with depth profiling using Ar⁺ sputtering. In the as-implanted state of the sample Fe was found to be present as Fe³⁺, Fe²⁺ and as metallic Fe⁰. This is in agreement with earlier conversion electron Mössbauer Spectroscopy measurements. For Ti-implanted YSZ in the as-implanted state the majority of the Ti is present as Ti⁴⁺, Ti³⁺, and Ti²⁺ ions, while a part of the Zr cations is present in the divalent oxidation state (Zr²⁺). After oxidation in air, the Fe and Ti ions are present only in the valence three and four oxidation states, respectively.     

On the Long Time Behavior of Infinitely Extended Systems of Particles Interacting via Kac Potentials

We analyze the long time behavior of an infinitely extended system of particles in one dimension, evolving according to the Newton laws and interacting via a non-negative superstable Kac potential (x)=(x), (0, 1]. We first prove that the velocity of a particle grows at most linearly in time, with rate of order . We next study the motion of a fast particle interacting with a background of slow particles, and we prove that its velocity remains almost unchanged for a very long time (at least proportional to ^–1 times the velocity itself). Finally we shortly discuss the so called Vlasov limit, when time and space are scaled by a factor .     

Near resonance charge transfer from a laser excited donor state

A laser induced charge transfer from Na(3p) to hydrogen-ions at different kinetic energies has been studied. An enhancement factor of about 90% in the production rate of Lyman-α radiation has been demonstrated to occur only with H⁺ and Na(3p) atoms reaction; no enhancement was observed with either H ₂ ⁺ or H ₃ ⁺ ions. Absolute cross-section for the production of Lyman-α radiation during the collision of H⁺, H ₂ ⁺ and H ₃ ⁺ ions and Na(3p) and Na(3s) atoms have been measured in the energy range 1–600eV. The charge exchange reactions involving hydrogen-ions and Na(3p) atoms created by two different methods have also been compared.     

A study of radiation damage by elastic scattering experiments

Abstract

Chaneling measurements are used to study the structure and configuration of defects produced in CdS under irradiation by 50–150 KeV Na⁺ ions at room temperature with a current density of 1 μA/cm² and irradiation dose 3.10¹⁵ ion/cm².

The results of studies of 1.8 MeV He⁺ ion dechaneling along the <1120> and <0001> axes are probably indicative of the defect structure extended along the <0001> axis.

For the dependence of the dechaneling cross-section on the ⁴He energy in the energy range 1.2 to 2.4 MeV we found E^?1, which characterizes the produced defects as randomly distributed complexes of interstitial atoms straining the crystal lattice.

The fact that the defects are mostly located along the <0001> direction can possibly be explained by strong anisotropy of CdS therefore the defects form the region of elastic stresses in the crystal which are maximum along the <0001> axis.     

Influence of the surface electric field in ion-beam-surface interaction at grazing incidence

We have measured the polarization of light emitted after ion surface scattering at small angle of incidence. The measurements are carried out with H⁺-, H ₂ ⁺ - and He⁺-ions under UHV-conditions with mono- and polycrystalline targets. We explain the typical variation of the polarization as “post collision Stark interaction” (PCSI) in the surface electric field, which can force transitions between nearly degenerate terms. The electric field is composed of two different contributions, a strong but short range surface field which is “seen” by atomsand ions and a long range but weak field due to the image charge which is “seen” to first orderonly by ions. The influence of the electric field on H-Balmer radiation is negligible at typical survival distances r_s≧0.35nm. But in contrast to H-atoms He⁺-ions feel the additional influence of the image field leading to a strong alteration of the polarization of the emitted light. The polarization of the Balmer-radiation stemming from Coulomb exploding H ₂ ⁺ -beams is observed to be modified by the electric field of the “spectator proton”.     

Slow and monoenergetic (3Heμ−)+ beam production and novel applications

Based upon the recent discovery at UT MSL/KEK, a new idea is proposed for producing a slow and monoenergetic (3.2 keV) (³He^–)⁺ ion beam by using particle decay of the (d³He) muon molecule formed during the (d) to³He transfer reaction. The proposed intense (³He) beam as well as the less intense (⁴He) beam will open up way to various new types of important CF experiments.     

Helium/hydrogen synergistic effect in reduced activation ferritic/martensitic steel investigated by slow positron beam

Here, we investigated the irradiation defect in reduced activation ferritic/martensitic steels by slow positron beam. Three ion-irradiation experiments were carried out: (i) He²⁺ irradiation, (ii) H⁺ irradiation and (iii) He²⁺ irradiation followed by H⁺ irradiation, at temperature 450?°C. The presences of vacancy defects, represented by ?S_He+H parameter, induced by sequential irradiations was larger than the sum of defects, ?S_He parameter + ?S_H parameter, caused by single He ions and single H ions. The synergistic effect of He and H was confirmed clearly from the perspective of positron annihilation spectroscopy.     

On the study of ion-acoustic solitary waves and double-layers in a drift multicomponent plasma with electron-inertia

Using the pseudopotential method, theoretical investigation has been made on the firstorder Korteweg-deVries ion-acoustic solitons in a multicomponent plasma consisting of warm positive ions, negative ions and isothermal electrons. The effects of electron-inertia and drift motion of the ions on the amplitudes and widths of the solitons have been studied in a plasma having (H⁺, Cl⁻), (H⁺, O⁻), (He⁺, H⁻) and (He⁺, O⁻) ions. Ion-acoustic double-layers have also been investigated for such plasmas. It has been found that drift velocity and electron-inertia have significant contribution on the formation of double-layers in multicomponent plasma     

A new channel of the concentration decay of doubly charged helium ions in a plasma

A model describing the decay of concentrations of excited helium atoms and ions taking into account doubly ionized helium is constructed on the basis of experimental data on excitation of a helium plasma by a pulsed electron beam. From this model, the rate constant of reaction He⁺⁺+He_m→He⁺+He ₀ ⁺ is estimated. It is found to agree in order of magnitude with theoretical estimates made in the framework of a model of polarization capture.     

Sequence of structural-phase states during implantation of C+, N+, and Si+ ions into molybdenum

The sequence of structural-phase changes in the surface layer of molybdenum during pulsed implantation of N⁺, C⁺, and Si⁺ ions has been studied. At radiation doses 5·10¹⁶ cm^–2 we detected qualitatively similar structural-phase transformations with the formation of highly dispersed secondary-phase particles (nitrides, carbides, and silicides), dislocations, point defects, and clusters of defects. At radiation doses (1–2)·10¹⁷ cm^–2 implantation of C⁺ and Si⁺ ions causes amorphization of the surface layer; nitrogen implantation is accompanied by the formation of continuous layers of the nitride phase on the surface.Siberian Physicotechnical Institute at the V. D. Kuznetsov State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 3–9, February, 1994.     

π-Meson production by photons at He3 in current-algebra model

In an analysis of the photoproduction of-mesons at He³ in the current-algebra model with hard-mesons, the amplitude for the process is derived with the help of the Ward identity, which follows from the hypothesis of the partial conservation of axial-vector current and current algebra. Only the-meson and the He³ and H³ nuclei are taken into account in the sums over intermediate states. The contact terms are important for an explanation of the experimental data. The differential cross sections are calculated for the photoproduction of ⁺-mesons at He³; they agree satisfactorily with the experimental data for low energies (E<240 MeV) and for low-momentum transfer (¦t¦<2.5 F^–2).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizikii, No. 7, pp.96–102, July, 1975.In conclusion the authors thank G. M. Radutskii for discussion of these results.     

Preferential sputtering of TIC under keV Ar+ ion bombardment: Simultaneous sputtering-ISS measurement with He+ and Ar+ ions

The composition change of the outermost atom layer of TiC(110) under ion bombardment with 1.5–3 keV He⁺ and He⁺ + Ar⁺ ions has been measured by ion scattering spectroscopy with He⁺ ions at different sample temperatures. It has been found that the preferential sputtering of C atoms takes place for both the He⁺ and Ar⁺ ion bombardment, however the preferred sputtering is more pronounced for Ar⁺ ions than for He⁺ ions. The ion bombardment with He⁺ ions at elevated sample temperatures hardly results in any change in surface composition below ～800°C, while Ar⁺ ion bombardment results in C enrichment for elevated temperatures as reported so far.     

Recombination channels of molecular ions He 2 + and electrons

The dependence of the intensities of atomic lines and molecular bands emitted in the afterglow of a helium discharge on the electron temperature is used to identify the processes in which states of He and He ₂ ^* are populated. It is established that the formation of He^* atoms (n = 3, 4) in decaying helium plasma occurs principally on account of the associative recombination of vibrationally excited He ₂ ⁺ ions and electrons. Analysis of the experimental reuslts leads to the conclusion that the distribution of the molecular ions He ₂ ⁺ over vibrational states is strongly nonequilibrium.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 67–72, February, 1984.It remains to thank N. P. Penkin for discussions and for his interest in the work.     

High resolution photon stimulated desorption spectroscopy of solid nitrogen by resonant N 1s core level excitation

Photon stimulated desorption (PSD) spectra of ions (N⁺, N⁺ ₂, and N²⁺) by N 1s 1 _g and N 1s Rydberg level excitations have been recorded from solid nitrogen for different polarization and detection conditions, and compared with electron yield data. Vibrational fine structure is clearly resolved also in photon stimulated desorption (PSD) spectra; its details depend on layer preparation, but also on the type of signal. Detailed evaluation should allow conclusions on the nature and the dynamics of the process of bond breaking and on the influence of the surroundings on it. Exploiting alignment effects by properly setting polarization and detection angles, symmetries of electronic excited states can be well analysed even for samples consisting of randomly oriented molecules.     

Effect of vibrational kinetics of He2 + ions on the afterglow of a discharge in helium

A decaying weakly ionized helium plasma [n_e=(0.2–1.1)·10¹¹ cm^–3, p=(40–70) mm Hg] was studied experimentally. It is shown that the experimental time dependences of the intensities of atomic lines and molecular bands in the afterglow phase can be explained if the vibrational kinetics of He₂ ⁺ ions is included in the analysis. Analysis of the measurements shows that for n_e 10¹¹ cm^–3 and N_a 10¹⁸ cm^–3 deexcitation of He₂ ⁺ ions occurs primarily as a result of inelastic collisions with helium atoms. Based on the experimental data, an approximate value was obtained for the rate constants of the vibrational relaxation of molecular helium ions 10^–16 cm³/sec. These results are used for making a qualitative analysis of the distribution of He₂ ⁺ ions over the vibrational states in the discharge phase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 88–96, November, 1986.     

Set theory and physics

Inasmuch as physical theories are formalizable, set theory provides a framework for theoretical physics. Four speculations about the relevance of set theoretical modeling for physics are presented: the role of transcendental set theory (i) in chaos theory, (ii) for paradoxical decompositions of solid three-dimensional objects, (iii) in the theory of effective computability (Church-Turing thesis) related to the possible solution of supertasks, and (iv) for weak solutions. Several approaches to set theory and their advantages and disadvatages for physical applications are discussed: Canlorian naive (i.e., nonaxiomatic) set theory, contructivism, and operationalism. In the author's opinion, an attitude of suspended attention (a term borrowed from psychoanalysis) seems most promising for progress. Physical and set theoretical entities must be operationalized wherever possible. At the same time, physicists should be open to bizarre or mindboggling new formalisms, which need not be operationalizable or testable at the lime of their creation, but which may successfully lead to novel fields of phenomenology and technology.     

Particle polarizations in decays of5HeΛ and4HΛhypernuclei

Nucleon polarizations are examined in the hypernucleus decays⁵He, ⁴He + p + _–,⁴H, ³H + p + _–, and⁴H, ³He + n + _–. The effect of the strong interaction in the final state is taken into account. A significant role is predicted for the resonance interaction in the p-⁴He system in the formation of the proton polarization in the⁵He decay. It is also shown that in the⁴H, ³H + p + _– decay the proton-polarization components should attain significant magnitudes, while in the charge-exchange decay⁴H, ³He + n + _–, the neutron polarization is expected to be not too large.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 100–103, October, 1988.