Showing papers in "Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms in 1989"

The Guelph PIXE software package IV

Abstract: Following the introduction of GUPIXWIN in 2005, a number of upgrades have been made in the interests of extending the applicability of the program. Extension of the proton upper energy limit to 5 MeV facilitates the simultaneous use of PIXE with other ion beam analysis techniques. Also, the increased penetration depth enables the complete PIXE analysis of paintings. A second database change is effected in which recently recommended values of L-subshell fluorescence and Coster–Kronig yields are adopted. A Monte Carlo code has been incorporated in the GUPIX package to provide detector efficiency values that are more accurate than those of the previous approximate analytical formula. Silicon escape peak modeling is extended to the back face of silicon drift detectors. An improved description of the attenuation in dura-coated beryllium detector windows is devised. Film thickness determination is enhanced. A new batch mode facility is designed to handle two-detector PIXE, with one detector measuring major elements and the other simultaneously measuring trace elements.

Cross sections for 170.5 ° backscattering of 4He from carbon for 4He energies between 1.6 and 5.0 MeV

Abstract: Cross sections for 170.5° backscattering of 4He ions by natural oxygen atoms in target films for 4He laboratory energies in the range 1.8–5.0 MeV have been measured. A thick (~ 35 keV) Al2O3 target film (~ 850 A), deposited on a carbon substrate and overcoated with ~ 200 A of Ta, was used for cross-section measurement in nonresonant regions. A thin (~ 6 keV) Ta/Nb/Al target film, containing 60% oxygen, was used in strong resonance regions. In both cases, the non-Rutherford 4He-O cross section was determined by comparison with the nearly Rutherford 4He-Ta cross section at the same energy. The cross sections were measured at maximum intervals of 50 keV, with smaller intervals used in the neighborhood of resonances. Results are given in graphical and tabular form; cross sections are given as ratios to the Rutherford cross section, with typical uncertainties of ± 2%; resonance energy uncertainties are typically ± 5 keV. Discrepancies between these and previous measurements are discussed.

Relation between structure and electronic properties of ion irradiated polymers

Abstract: Ion beam irradiation of saturated polymers leads to the formation of new carbonaceous materials exhibiting enhanced electrical conductivity and increase of the optical absorption, which shifts gradually from the near UV to the visible. Different techniques, such as the analysis of the gas evolved from the polymer during irradiation, RBS and ERDA show the loss of the more volatile elements which results from the dissociation of the molecular structure. The consideration of different types of polymers indicates that some specific structural elements are preserved and that unsaturated bonds appear at high fluences, which are responsible for the loss of the insulating properties of polymers. The chemical bond modifications are discussed in view of infrared spectroscopy and ESCA, which shows the formation of graphite-like phases in polyimide and explains the high level of conductivity reached in this type of polymers. The appearance of conducting properties cannot be described by a simple model of carbonization and are governed both by the molecular structure of the parent polymer and the beam conditions. The behaviour of polyimide will be considered more in details because of the remarkable level of conductivity ( σ = 10 3 S/cm) and heat stability reached upon irradiation with heavy ions, which render this type of surface processing very efficient in order to produce conductive polymers.

The use of an electron beam ion trap in the study of highly charged ions

Abstract: The Electron Beam Ion Trap (EBIT) is a relatively new tool for the study of highly charged ions. Its development has led to a variety of new experimental opportunities; measurements have been performed with EBITs using techniques impossible with conventional ion sources or storage rings. In this paper, I will highlight the various experimental techniques we have developed and the results we have obtained using the EBIT and higher-energy Super-EBIT built at the Lawrence Livermore National Laboratory.

Accurate site populations from Mössbauer spectroscopy

Abstract: All major aspects of the problem of obtaining site populations from Mossbauer spectroscopy are addressed. A powerful analytic method for deconvoluting the transmission integral is developed and many new single line thickness effect results are given. The intrinsic absorber cross section is first obtained by our deconvolution and tailored filtering method. The site-specific spectral contributions to the cross section are then distinguished to the extent that this is possible. Corresponding spectral areas are exactly proportional to products of site-specific effective recoiless fractions and the required populations. Methods for obtaining the required recoiless fractions are described. Experimental self-consistency tests are suggested and all relevant underlying assumptions are discussed.

Partitioning of ion-induced surface and bulk displacements☆

Abstract: An analytical method is described to determine the number and partitioning of displacements of surface and bulk atoms by low energy ions incident on a solid. Results are presented for Ge, Si and C (diamond and graphite). For Ge the results are compared with Monte Carlo calculations using the computer code TRIMRC. Good agreement is found in this comparison, thereby verifying the adequacy of several approximations introduced into the formalism. Displacement threshold and surface-to-bulk displacement ratio contours are presented as a function of ion mass and energy based on our analytic calculations. Comparison of these contours with recent experimental results for Si suggests that this approach provides a global framework for understanding and optimizing the effects of low-energy ions on semiconductor expitaxial growth.

Bombardment-induced compositional change with alloys, oxides, oxysalts, and halides

Abstract: Compositional changes in bombarded alloys are now recognized to arise mainly from bombardment-induced segregation, “BIS” and to only a limited extent from preferential sputtering, i.e. from differences in mass, chemical binding, or volatility. The significant relation is α A (2) α B (2) = (α A (2′) α B (2′) ) K b , where α is the atom fraction, A and B are the components of the alloy, 2 designates atom layer one , 2′ designates atom layer two and K b is the BIS ratio. A very similar relation holds for equilibrium segregation except that K b is replaced with K eq , equivalent to exp ( ΔG seg / kT ). It is shown that K b and K eq are always in the same sense except for NiPt, that K b lies in the interval 1.25 ⩽ K b ⩽ 5.4 for 14 out of 16 different systems and that for ambient temperature the inequality K b ⪡ K eq holds. Most aspects of the relation between K b and K eq can be understood if BIS is caused by chemically guided final steps in some ballistic trajectories. Such a mechanism also accounts for what is otherwise a paradox, namely that the driving force for segregation is so small, ranging from 0.06 eV for CuPd to 0.52 eV for AuNi. The latter values are similar to heats of mixing, proposed by Cheng et al. to govern ion-beam mixing and to differences of heats of formation, proposed by the present author to govern chemical changes in oxides and oxysalts.

Scintillators for well logging applications

Abstract: The hostile environmental conditions and limited space in the borehole requires gamma-ray detectors with special properties which are not usually important in laboratory applications. Since the borehole temperature can exceed 200° C, scintillators with inherently good temperature responses are desirable. Lower scintillation output at high temperature affects signal-to-noise, energy resolution and gain control. The scintillation decay time also usually depends on temperature, thus affecting pulse shaping and counting rate. Due to the shock and vibration encountered in the borehole, mechanically rugged and nonhygroscopic scintillators are preferred to avoid the need for special packaging that reduces crystal size and performance. Most well logging applications benefit from scintillators with high gamma-ray detection efficiency which results from high atomic number and high density. In order to take advantage of high detection efficiencies and the resulting high counting rates, a short scintillation decay time is necessary to minimize pulse pileup.

First experiments with the heidelberg test storage ring TSR

Abstract: The Heidelberg heavy ion test storage ring TSR started operation in May 1988. The lifetimes of the ion beams observed in the first experiments can be explained by interactions with the residual gas. Multiple Coulomb scattering, single Coulomb scattering, electron capture and electron stripping are the relevant processes. Electron cooling of ions as heavy as O 8+ has been observed for the first time. With increasing particle number, the longitudinal Schottky noise spectrum becomes dominated by collective waves for cooled beams, allowing a determination of velocities of sound. After correcting for these coherent distortions fo the Schottky spectrum, the longitudinal beam temperature could be extracted. The observed longitudinal equilibrium beam temperatures increase strongly with the charge of the ions. For a cooled C 6+ beam, temperatures a factor of 120 higher were measured compared to a proton beam with the same particle number. The shrinking of the beam diameter due to electron cooling was observed with detectors which measured the profile of charge-changed ions behind a bending magnet. A strong laser-induced fluorescence was detected when storing metastable 7 Li + ions in the ring. Via the Doppler effect a very accurate measurement of the ion velocity profile could be performed. First attempts to observe laser cooling failed, probably due to heating effects from intrabeam scattering and a coupling between longitudinal and transversal motion in the beam. Several experiments under preparation are outlined.

Recent progress in understanding ion-beam mixing of metals

Abstract: Recent progress in three fundamental areas related to the ion-beam mixing of metal targets is reviewed: (1) molecular dynamics simulations of the temporal development of energetic displacement cascades; (2) the substantially increased mixing efficiencies that have been reported in many systems at intermediate irradiation temperatures; and (3) amorphization during ion irradiation. Significant advances in our fundamental understanding have occurred in all three of these areas in the past few years. Mass transport at various times during the evolution of energetic displacement cascades in Cu and Ni has been calculated recently using fully dynamic computer simulations. These results, discussed in section 2, strongly support the conclusion drawn from earlier experimental work that a majority of ion-beam mixing occurs at low (1–2 eV) atomic recoil energies during the cascade cooling phase. In section 3, characteristic differences are identified between radiation-enhanced diffusion, that is mass transport due to freely-migrating vacancy and interstitial defects and the enhanced ion-beam mixing that has been observed in many materials at intermediate temperatures. It is argued here that true radiation-enhanced diffusion should be observable only at substantially higher temperatures. Finally, recent measurements of the shear elastic constant, the lattice parameter and the long-range order parameter during ion-induced amorphization of highly-ordered intermetallic compounds are summarized in section 4. This new information indicates that ion-induced amorphization is preceded by a first-order phase transformation triggered by an elastic instability and reveals several parallels between solid-state melting and amorphization phenomena.

Scanning tunneling microscopy study of single-ion impacts on graphite surface

Abstract: Cleaved surfaces of highly oriented pyrolitic graphite were implanted with 50 keV-Ar + and 150 keV-Xe 3+ ions at a dose of S × 10 11 cm −2 . The surface damages due to single ion impacts were examined by scanning tunneling microscopy. Ion impacts are revealed by the formation of hillocks on the graphite surface. They are attributed to residual damages and defect-induced stresses due to the cascade collision of implanted ions.

Transition from localized defects to continuous latent tracks in magnetic insulators irradiated by high energy heavy ions: A HREM investigation

Abstract: Lattice imagery has been applied to the investigation of radiation defects induced by 3.5 GeV Kr ions and 3.1 GeV Xe ions in magnetic insulators. The structure dependence of the defects on the energy deposited by electronic stopping is clearly established, varying from continuous latent tracks towards isolated and spherical defects, when the deposited energy changes through a threshold value which characterizes each compound.

The performance of a 5 metre normal incidence monochromator at the Daresbury Laboratory Synchrotron Radiation Source

Abstract: The characteristics and performance of a 5 metre normal incidence monochromator used for gas phase experiments are given, together with a description of the pre- and post-monochromator focusing optics. Measurements have been performed to determine the absolute photon flux output and the contribution from higher orders of radiation. Highlights are given of the experimental programme in photochemistry and photophysics.

In situ ion irradiation /implantation studies in the HVEM-tandem facility at argonne national laboratory

Abstract: The HVEM-Tandem User Facility at Argonne National Laboratory interfaces two ion accelerators, a 2 MV tandem accelerator and a 650 kV ion implanter, to a 1.2 MV high-voltage electron microscope. This combination allows experiments involving simultaneous ion irradiation/ion implantation, electron irradiation and electron microscopy/electron diffraction to be performed. In addition the availability of a variety of microscope sample holders permits these as well as other types of in situ experiments to be performed at temperatures ranging from 10 to 1300 K, with the sample in a stressed state or with simultaneous determination of electrical resistivity of the specimen. This article summarizes the details of the Facility which are relevant to simultaneous ion beam material modification and electron microscopy, presents several current applications and briefly describes the straightforward mechanism for potential users to access this US Department of Energy-supported facility.

Determination of concentration profiles by elastic recoil detection with a ΔE−E gas telescope and high energy incident heavy ions

Abstract: The Elastic Recoil Detection (ERD) method has been used to determine the profile of a wide range of elements simultaneously in a thin layer (1 μ m) with a depth resolution of a few hundred A and high sensitivity. Z separation is achieved by a ΔE (gas)- E (solid) telescope. Results for 127 I (up to 240 MeV) incident ions used to profile thin films of dielectrics (SiO x N y H z ), amorphous semiconductors (a-GaAs: H) and superconductors (YBaCuO, BiSrCaCuO) are reported. It has been considered previously that ERD is of interest for analysis of light elements. We show that high energy heavy incident ions extend the field of application of the ERD method to all elements with an approximately constant depth resolution and sensitivity.

Glow plasma treatment at atmospheric pressure for surface modification and film deposition

Abstract: A plasma treatment at atmospheric pressure was developed employing a stable glow plasma at atmospheric pressure under selected conditions. The structure of the electrode, the kind of dilute gas, and the frequency of power were controlled. The surface fluorination of PET (polyethylene terephthalate) film, carbon thin film deposition and polymerization of ethylene by such a plasma are described here. The surface energy could be controlled by plasma treatment at various concentrations (O 2 /CF 2 /He). The ageing effect has been observed for 9 months by measuring the contact angle of a water drop on the surface and surface composition by XPS. The friction coefficients were measured at the fluorinated surface.

Accurate efficiency determination of a Si(Li) detector in the Si-K and Au-M absorption edge energy region

Abstract: The particle-induced X-ray emission (PIXE) method with use of thin evaporated and ion-implanted targets and 1H and 4He ion impact, combined with the standard X-ray source technique, is applied to determine the efficiency of a Si(Li) detector in the photon energy range 1.5–150 keV. An existing database for the efficiency determination by PIXE method is discussed in detail. Special care has been devoted to the reliable reproduction of the Si-K and Au-M absorption edge structure which strongly affect the low-energy part (1.5–4 keV) of the efficiency curve. For this purpose, it has been found necessary to measure the thickness of the detector Au contact by the fluorescence method, to fit then uniquely the thickness of a uniform Si dead-layer. It has been also demonstrated that the observed efficiency increases in the intermediate photon energy region (6–20 keV) can be well described assuming the existence of an additional peripheral Si dead-layer. An extended Si(Li) detector model including this effect is proposed. The procedure developed for the efficiency determination is applied to monitor the Si(Li) detector parameters over a year. During which the increase of an ice build-up layer with time was observed.

Round Robin computer simulation of ejection probability in sputtering

Abstract: We have studied the ejection of a copper atom through a planar copper surface as a function of recoil velocity and depth of origin. Results were obtained from six molecular dynamics codes, four binary collision lattice simulation codes, and eight Monte Carlo codes. Most results were found with a Born-Mayer interaction potential between the atoms with Gibson 2 parameters and a planar surface barrier, but variations on this standard were allowed for, as well as differences in the adopted cutoff radius for the interaction potential, electronic stopping, and target temperature. Large differences were found between the predictions of the various codes, but the cause of these differences could be determined in most cases. A fairly clear picture emerges from all three types of codes for the depth range and the angular range for ejection at energies relevant to sputter ejection, although a quantitative discussion would have to include an analysis of replacement collision events which has been left out here.

Depth of origin and angular spectrum of sputtered atoms

Abstract: A theoretical analysis is presented of the depth of origin of atoms sputtered from a random target. The physical model aims at high energy sputtering under linear cascade conditions and assumes a dilute source of recoil atoms. The initial angular distribution of the recoils is assumed isotropic, and their energy distribution is E−2 like without an upper or lower cutoff. The scattering medium is either infinite or bounded by a plane surface. Atoms scatter according to the m = 0 power cross section. Electronic stopping is ignored. The sputtered flux, differential in depth of origin, ejection energy and ejection angle has been evaluated by Monte Carlo simulation and by five distinct methods of solution of the linear Boltzmann equation reaching from continuous slowing down neglecting angular scattering to the P3 approximation and a Gram-Charlier expansion going over spatial moments. The continuous slowing down approximation used in previous work leads to results that are identical to those found from a scheme that only ignores angular scattering but allows for energy loss straggling. Moreover, these predictions match more closely with the Monte Carlo results than any of the approximate analytical schemes that take account of angular scattering. The results confirm the common assertion that the depth of origin of sputtered atoms is determined mainly by the stopping of low energy recoil atoms. The effect of angular scattering turns out to be astonishingly small. The distributions in depth of origin, energy, and angle do not depend significantly on whether the scattering medium is a halfspace or an infinite medium with a reference plane. The angular spectrum comes out only very slightly over cosine from the model as it stands, in agreement with previous experience, but comments are made on essential features that are not incorporated in the physical model but might influence the angular spectrum. An improved set of constants matching the standard power cross section to Born-Mayer scattering brings the depth of origin of sputtered atoms into close numerical agreement with results from more realistic simulation models.

The new Oxford scanning proton microprobe analytical facility

Abstract: A purpose-built scanning proton microprobe facility has been established for multidisciplinary research at the University of Oxford. 1–3.8 MeV beams of protons with currents of up to 150 pA focused into submicron-sized probes can now be obtained for production of high-resolution PIXE and BS maps of samples from a wide range of applications. This article briefly describes the system hardware as well as results achieved during the commissioning stage of the facility. Further development work is now directed towards achieving 100 nm probes and, as part of this work, a novel quadrupole lens has been developed which, when used in a doublet or triplet system, achieves submicron resolution. Measurement of the aberrations of these quadrupoles, using the grid shadowmethod, showed negligible parasitic aberration below fifth order. The results are compared to similar measurements performed on the quadrupoles of the original probe-forming lens system.

Use of the D(3He,P)4 He reaction to study polymer diffusion in polymer melts

Abstract: By measuring the diffusion coefficient of a deuterated polystyrene in a hydrogenated polystyrene, we demonstrate the use of the D(3He,p)4He reaction to profile deuterium in polymers. Evaluation of the technique shows that with a 3He beam energy of 2 MeV, the beam at normal incidence to the sample and a detector angle of 160°, depths of 8 μm can be profiled, with a resolution of 390 nm at the surface and 420 nm at 8 μm. At the other extreme with a beam energy of 0.7 MeV and a glancing angle of incidence of 15° a resolution of 30 nm can be achieved at depths of up to 0.2 μm. The capability of the technique is compared with the ion beam technique more commonly used for profiling deuterium: elastic recoil detection analysis.

The argonne fragment mass analyzer

Abstract: The Fragment Mass Analyzer is being constructed for use in heavy-ion experiments with the ATLAS superconducting linear accelerator system at Argonne National Laboratory. It is a triple-focussing recoil mass spectrometer, designed to separate nuclear reaction recoils from the primary heavy-ion beam and disperse them in M/Q (mass/unit charge) at the focal plane. The main ion-optical elements are two electric dipoles and a magnetic dipole, with the electric dipoles (E) symmetrically placed before and after the magnet (M). The elements are spaced such that the position energy dispersion (x/delta/sub E/) and the angle energy dispersion (theta/delta/sub E/) of the system both vanish (energy focus). Here delta/sub E/ stands for ..delta..E/E, the fractional energy deviation from the central energy. The energy-dispersionless EME configuration was first used by Cormier and Stwertka for the Recoil Mass Spectrometers at Rochester, and was also chosen by Spolaore et al. for the Recoil Mass Spectrometer at the Laboratori Nazionali di Legnaro in Padua. Although the energy dispersion is canceled, the M/Q dispersion is not, and the device performs as a mass spectrometer. When used in the energy-dispersionless mode, the EME combination of elements offers some distinct advantages over designs containing Wien filters or a single electrostatic element.more » These advantages include wider M/Q and energy acceptances and superior rejection of the primary beam (/approximately/10/sup /minus/12/). The energy focus condition implies isochronous orbits for particles having the same M/Q and energy but with differing emission angles at the target, an important feature when used with pulsed beam accelerators like ATLAS. 8 refs., 4 figs., 1 tab.« less

Production of stable and radioactive nuclides in thick stony targets (R = 15 and 25 cm) isotropically irradiated with 600 MeV protons and simulation of the production of cosmogenic nuclides in meteorites

Abstract: Two artificial meteoroids made out of gabbro with a density of 3 g cm−3 with radii of 15 and 25 cm were isotropically irradiated with 600 MeV protons in order to simulate the production in meteoroids of cosmogonie nuclides by galactic cosmic ray protons. The depth dependent production of a wide range of radionuclides from target elements O, Mg, Al, Si, Ti, Fe, Co, Ni, Cu, Ba, Lu, and Au was measured. Furthermore, the production of He and Ne isotopes from Al, Mg, Si as well as from degassed meteoritic material was determined. Together with earlier results on an artificial meteoroid with a radius of 5 cm, and with data derived from thin-target experiments, the depth dependence of production rates is investigated for radii from 0 to 75 g cm−2. 60Co from Co shows the strongest size dependence; the center production rates differ by a factor of 100 for radii of 5 and 25 cm. Other low-energy products, like 58Co from Co and 24Na produced from Al, increase only up to a factor of 3.5 over the entire range of radii. For extreme high-energy products, in contrast, the center production rates decrease by up to a factor of 10. The observed depth profiles show a wide varity of shapes. Low-energy products have pronounced maxima in the center, high-energy products exhibit strong decreases from surface to center and, in between, essentially flat profiles are seen as well as such with a transition maximum. The spectra of primary protons and of secondary protons and neutrons in the artificial meteoroids were calculated using Monte Carlo techniques. The fluxes of secondary protons and neutrons depend strongly on depth and size, the spectral shapes being different for protons and neutrons. Calculating also the nucleon spectra which result from irradiation with real GCR p-spectra, the differences between simulation experiments and cosmic irradiation conditions are quantitatively described. On the basis of all these spectra and of thin-target excitation functions, production rates were calculated and compared with the experimental ones. The theoretical depth profiles allow to distinguish the different contributions of primary and secondary particles and to unravel the various production modes of cosmogenic nuclides in meteoroids. Our investigation shows that it is possible to model the production of residual nuclides in artificial meteoroids with excellent accuracy by thin-target calculations, provided that reliable thin-target excitation functions are at hand.

Semi-empirical formulae for heavy ion stopping powers in solids in the intermediate energy range

Abstract: A semi-empirical procedure to compute heavy ion electronic stopping powers is presented. The calculations use stopping powers for alpha particles and a new parameterization for the effective charge which is deduced from a set of about 600 experimental stopping power values covering an energy range from 3 to 80 MeV/A for 15 incident heavy ions and 18 solid stopping materials.

Recent developments in low-energy ion scattering spectroscopy (ISS) for surface structural analysis

Abstract: Recent years have seen significant progress in low-energy ion scattering spectroscopy (ISS) for surface structural analysis. They include the development of impact-collision ion scattering spectroscopy (ICISS) to make quantitative surface structural analysis possible and the use of alkali ions rather than noble-gas ions in ICISS (ALICISS) to avoid the ambiguity of ion neutralization probability. The latest progress is the development of coaxial impact-collision ion scattering spectroscopy (CAICISS) in which a pulsed-beam ion source and a time-of-flight energy analyzer are arranged coaxially so as to take the experimental scattering angle just at 180°. Various characteristics of CAICISS, which are due to (a) the 180° experimental scattering angle, (b) the time-of-flight mode for the energy analysis, and (c) the use of an acceleration tube for scattered ions, are discussed.

Triple ion beam irradiation facility

Abstract: A unique ion irradiation facility consisting of three accelerators is described. The accelerators can be operated concurrently to deliver three ion beams on one target sample as large as 100 mm2 in area. The energy ranges of the ions are 50 to 400 keV, 200 keV to 2.5 MeV and 1.0 to 5.0 MeV, which allows three different ions in the appropriate mass range to be simultaneously implanted to the same depth in a target specimen. Typical depth ranges are 0.1 to 1.0 μm. The X-Y profiles of all three ion beams are measured by a system of miniature Faraday cups. The ion beam energy of the low voltage accelerator can be ramped periodically during the implantation. Three different types of target chambers are in use at this facility. A triple-beam high vacuum chamber can hold nine TEM specimens at controlled temperatures in the range 400–800 °C during an irradiation by the three simultaneous beams. A second high vacuum chamber on the medium voltage accelerator beam line houses a low- and high-temperature translator and a two-axis goniometer for ion channeling measurements. The third chamber on the high energy beam line can be gas-filled for special stressed specimen irradiations. Applications of this facility to surface modification of materials are described.

A new type of rf electron accelerator: The rhodotron

Abstract: In the median plane of a cavity resonator derived from a λ/2 coaxial line short-circuited at both ends the magnetic field is zero and the electric field is radial. Therefore it is possible to accelerate charged particle beams crossing diametrically the cavity within this plane without parasitic deflections. By appropriate bending of the beam outside of the cavity by magnets, n successive accelerations are performed, so that the shunt-impedance is increased by a factor of n2. Optimization of the shunt-impedance achieved by taking into account the phase stability conditions determines the dimensions of the device for a given n. Proper shaping of the magnet edges produces a suitable focussing. Such a machine, a prototype of which is under completion, turns out to be very convenient for accelerating 20–500 kW electron beams to energies in the 1–20 MeV range.

Backscattering of Atomic and Molecular Hydrogen from Nickel and Carbon

Abstract: Nickel and carbon targets were bombarded perpendicularly with H+, H2+, H+3, D+, D+2 and D+3 ions at energies ra keV to 20 eV/nucleon. The energy distributions of backscattered neutral atoms were measured at a scattering angle of 135° with a time of flight (TOF) technique. The energy distributions obtained from molecular ion bombardment are broader than those obtained from H+ or D+ Assuming a cosine angular distribution, the particle reflection coefficients are determined from the measured energy distributions. The comparison of the experimental results with computer simulations shows that good agreement is obtained when hydrogen implantation is taken into account.