Sputtering angle effects by Kr mixing in N+ ion beam on the lifetime of nitrided carbon stripper foils

Nitrided carbon stripper (NCS) foils with high nitrogen content were produced by ion beam sputtering of reactive nitrogen gas. Such foils seem to be very useful as strippers in high-intensity heavy ion accelerators. We have conducted comprehensive research, development, and production of such foils with high reproducibility. Krypton, a heavy noble gas, was mixed with the reaction nitrogen gas (IBSRN) in the ion beam sputtering process to produce stripper foils with short sputtering deposition time and long lifetimes in the high intensity ion beam irradiation. With the (N₂ + Kr) mixed gas ions we investigated the influence of different sputtering angles (α) on the lifetime of the NCS-foils in case of poly-graphite material. The lifetime measurement of these foils of 20 ± 5 μg/cm² was performed with a 3.2 MeV Ne⁺ ion beam as usual. The foils made at a sputtering angle of 15° showed a maximum of 11.0 and 7.5  C/cm² average charge density, respectively, which corresponded to about 275 and 187 times the lifetime of the best commercially available foils.     

Novel use of an isotope separator to determine the position of fluorine-18 in labelled 1,1,1,2-tetrafluoroethanes

A novel technique is described for measuring the site selectivity of methods for labelling the major CFC-alternative, 1,1,1,2-tetrafluoroethane (HFA 134a), with fluorine-18 (t_1/2 = 109.7 min). The carbon–carbon bond in radiofluorinated HFA 134a is broken in the ion source of an isotope separator. Radioactivity associated with the ion beam of the [CF₂ ¹⁸F]^+. fragment (m/z = 68) is collected, measured and divided by the integrated mass of the simultaneously collected ion beam for the [CF₃]^+. fragment (m/z = 69) to give the ‘specific radioactivity’ (in nCi nmol^–1) of the radiolabel in the 1-position. Similarly, the ‘specific radioactivity’ of the radiolabel in the 2-position is calculated from the measured radioactivity of the ion beam from the [CH₂ ¹⁸F]^+. fragment (m/z = 32) and the integrated mass of the simultaneously collected ion beam from the [CH₂F]^+. fragment (m/z = 33). The selectivity of the labelling procedure for a particular position is then given by the decay-corrected ratio of specific radioactivity at that position to the sum of specific radioactivities. The labelling of HFA 134a by the reaction of [¹⁸F] fluoride with trifluoroethylene was found to have 97% selectivity for the CF₃ group, whereas labelling by the reaction of [¹⁸F] fluoride with 2,2,2-trifluoroethyl p-toluenesulphonate was found to have 91% selectivity for the CH₂F group. This information is of value for tracer studies of the fate of HFA 134a in man following its inhalation as a drug propellant. The described technique is of potentially wider value for determining the position of fluorine-18 in labelled polyfluorinated molecules.     

CO2 Activation by Zr+ and ZrO+ in Gas Phase

The gas-phase reduction of carbon dioxide to carbon monoxide, induced by Zr⁺ and ZrO⁺ catalysts, was investigated at density functional level of theory. Calculations were carried out using both hybrid and pure exchange-correlation functionals in order to reproduce adequately the energetic gap between the Zr^{+ 4}F and ²D electronic states and experimental reaction heats. In agreement with a guided ion beam tandem mass spectrometer study, we have found that carbon dioxide activation by Zr⁺ presents a spin-forbidden mechanism because of a spin inversion process occurring during reaction in the rate- determining step. ZrO⁺ interacts with CO₂ through two possible pathways both endothermic: formation of ZrO ₂ ⁺ and CO products is less unfavourable. Information about ground and excited states of ZrO⁺ and ZrO ₂ ⁺ oxides and bond dissociation energies of species present on the reaction paths was also given.     

Determination of carbon in thin layers by means of the12C(d,n)13N nuclear reaction using a 2 MeV Van de Graaf accelerator

A nondestructive method for carbon determination in layers of 3–10 m thickness is considered. The method is based on using the¹²C(d, n)¹³N nuclear reaction with simultaneous account of surface contamination by means of the¹²C(d, p)¹³C competitive reaction. The total cross sections for the¹²C(d, n)¹³N reaction were measured from 0.4 to 1.7 MeV. Proton beam annealing was applied with the purpose of lowering surface carbon content. The detection limit of carbon by this method is 0.5 ppm, relative standard deviation is 0.06. Disturbing effects of carbon diffusion and¹³N recoil backs cattering are also taken into account.     

Decomposition of a cation exchange resin with hydrogen peroxide

Ion exchange resins are widely used in the field of nuclear industry. The present work aimed at the development of a method for complete decomposition of cation exchange resins with H₂O₂ in the presence of Fe³⁺ ion. The decomposition reaction proceeded at ambient temperature and decomposition time was greatly shortened with increasing concentration of Fe³⁺ ion rather than that of H₂O₂. The catalytic action of Fe³⁺ ion was suppressed with increase of HNO₃ concentration. As much as 4 g of the air-dried resin could be decomposed with 8 ml of 30% H₂O₂, and the use of about 60 ml of 30% H₂O₂ resulted in the complete decomposition of organic carbon to CO₂. Absence of any orgnaic carbon in the residual solution will simplify the final disposal.     

Direct synthesis of radioactive carbon labeled fullerences using nuclear reactions

The¹¹C and¹⁴C labeled fullerenes were produced by charged-particle and neutron irradiation, of C₆₀, C₇₀ and their mixture. It was found that a carbon atom of fullerence can be easily exchanged with a radioactive carbon atom produced by a nuclear reaction. The HPLC method was effective for identification and purification of various labeled fullerene families as chemically stable compounds. The radiochemically interesting aspect of the results is not only the production of¹¹C and¹⁴C labeled fullerenes but also the formation of radioactive higher fullerenes which can be simultaneously produced with high yield and in carrier-free form.     

Effect of accelerators on thoria based nuclear fuels for rapid and quantitative pyrohydrolytic extraction of F? and Cl? and their simultaneous determination by ion chromatography

Pyrohydrolysis is a fast, reliable and convenient method for the decomposition of solid refractory samples. Thoria based mixed oxide nuclear fuels requires more than 1,200?°C reaction temperature to lose its structural integrity so as to release the halides. In the present paper, we report WO₃ accelerated pyrohydrolytic extraction technique for the separation of F^? and Cl^? from thoria based fuels along with the feasibility of using MoO₃ and V₂O₅. The mechanism of extraction has been investigated in detail using X-ray diffraction and recovery studies. ThO₂ along with its halides undergo high temperature solid state reaction with WO₃ forming Th(WO₄)₂ and releasing the halides for their subsequent hydrolysis. The quantification was carried out by ion chromatography with suppressed ion conductivity detection. The average recoveries of the spiked samples for F^? and Cl^? were 93?C99%. The method was successfully applied for simultaneous determination of F^? and Cl^? in thorium based nuclear fuel samples at 950?°C.     

Repair of defects created by Ar+ sputtering on graphite surface by annealing as confirmed using ToF‐SIMS and XPS

Defects were created on the surface of highly oriented pyrolytic graphite (HOPG) by sputtering with an Ar⁺ ion beam, then characterized using X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) at 500°C. In the XPS C1s spectrum of the sputtered HOPG, a sp³ carbon peak appeared at 285.3 eV, representing surface defects. In addition, 2 sets of peaks, the C_x⁻ and C_xH⁻ ion series (where x = 1, 2, 3...), were identified in the ToF‐SIMS negative ion spectrum. In the positive ion spectrum, a series of C_xH₂^+• ions indicating defects was observed. Annealing of the sputtered samples under Ar was conducted at different temperatures. The XPS and ToF‐SIMS spectra of the sputtered HOPG after 800°C annealing were observed to be similar to the spectra of the fresh HOPG. The sp³ carbon peak had disappeared from the C1s spectrum, and the normalized intensities of the C_xH⁻ and C_xH₂^+• ions had decreased. These results indicate that defects created by sputtering on the surface of HOPG can be repaired by high‐temperature annealing.     

[C]+· and [CH]+ from doubly charged ions formed from malononitrile

The metastable ions [M]²⁺, [M – H]²⁺· and [M – H₂]²⁺ from malononitrile fragment by loss of [CH]⁺, [C]⁺· and [C]⁺·, respectively. The reaction of the molecular ion involves the methylene and nitrile carbon atoms in the statistical probability ratio, while that of [M – H]²⁺· involves exclusively the nitrile carbon and that of [M ? H₂]²⁺ involves an approximately equal contribution, from both sources. It is suggested that the metastable molecular ion fragments through a bipyrimidal intermediate.     

Studies in heavy ion activation analysis trace determination possibilities with9Be bombardment

⁹Be induced radioactivation was used to study the trace determination of 19 elements at 3 different ion beam energies (E_lab=14, 32 and 63 MeV⁹Be²⁺). Nine nuclear reactions, yielding radionuclides with half-lives longer than 2.5 m, present potential analytical features. Beside the very sensitive detection of B and N, the multielemental determination of Na, Si, Ca, Sc, and Zn is possible with a⁹Be ion beam of appropriate incident energy. Nuclear interferences have also been investigated and quantified.     

Characterisation of 13C implantations in silicon by NRA [13C(p,γ)14N] and RBS

SiC_X layers close to the surface have been produced by implanting 40 keV ¹³C ions into silicon with a fluence of 6×10¹⁷ at./cm² (j=12 μA/cm²) at room temperature (RT). Depth distributions and areal densities (doses) of the implanted carbon have been analysed by the nuclear reaction ¹³C(p,γ)¹⁴N (NRA) which shows a sharp resonance in the excitation function at a proton energy of 1748 keV (Γ=75 eV FWHM). The depth resolution at the surface amounts to 31 nm due to energy spread of the proton beam (1.2 keV FWHM) and resonance width. The surface resolution of the NRA can be increased up to 8 nm when tilting the sample (surface normal) to an angle of 75° with respect to the proton beam direction. Using a NaI detector the detection limit of ¹³C in silicon is approximately 1 at.%. Comparative elastic backscattering measurements with ⁴He⁺ projectiles were performed at 2 MeV (Rutherford backscattering spectroscopy, RBS) and 3.45 MeV (high energy backscattering, HEBS) at a backscattering angle of 171°. The measured ¹³C depth distributions have been compared with a distribution calculated by the Monte Carlo algorithm T-DYN.     

Influence of the Native Oxide Layer on the Silicon Surface During Initial Stages of Nitridation

 Thin SiO₂ layers were produced by thermal oxidation of Si wafer material. To study the effect of nitridation on the oxide layers, the specimens were nitrided in a furnace at high temperature. Non-destructive ion beam analysis was performed to determine changes in the elemental concentrations and depth profiles of the major components. In particular, N and O concentrations were measured using the non-resonant nuclear reactions ¹⁴N(d, α)¹²C and ¹⁶O(d, p)¹⁷O, respectively. To obtain depth profiles of the as-prepared and nitrided specimens, the samples were measured with RBS and heavy ion elastic recoil detection analysis. The ion beam analyses revealed an increase in thickness of the SiO₂ layers with temperature. The specimens nitrided at 1200 °C were almost free of N. Surface topology investigations with scanning electron microscopy revealed concentric annular artificial patterns at the surfaces. In the centre of the pattern, only silicon was measured. Additionally, a band consisting of Si, O, and N surrounding the pattern was discovered. The findings are in agreement with specimens prepared at higher temperatures. Received June 19, 2000. Revision December 9, 2000.     

Etching Efficiency for Si and SiO2 by CF+x,F+, and C+ Ion Beams Extracted from CF4 Plasmas

Fluorocarbon (CF⁺ _x), fluorine (F⁺), and carbon (C⁺) ion beams with highcurrent density (50i<800 A/cm²) were irradiated to Si and SiO₂surfaces to investigate the influence of the ion species on the etchingefficiency. The ion beams were extracted from magnetized helicon-wave CF₄plasmas operated in pulsed modes. The CF⁺ ₃ beam had the largest etchingefficiency for Si at the same beam energy. When the same data weresummarized as a function of the momentum of the incident ion beam, thedifference in the etching efficiency became small, although the CF⁺ ₃ beamstill had a slightly larger etching efficiency. On the other hand, theetching efficiency for SiO₂ by the CF⁺ ₃ beam was larger than that by theother ion beams in the low-momentum region. In addition, in the low-momentumregion, the etching efficiency for SiO₂ by CF⁺ ₃ was larger than that forSi. These results suggest the high chemical reactivity of CF⁺ ₃ with SiO₂,leading to the high etching selectivity of SiO₂ over underlying Si in thefabrication of semiconductor devices.     

Über Chalkogenolate. 159. Umsetzung von 1,2-Ethandithiolaten mit Kohlenstoffdisulfid 1. Darstellung und Eigenschaften von 1,2-Ethan-bis(trithiocarbonaten)

On Chalcogenolates. 159. Reaction of 1,2-Ethanedithiolates with Carbon Disulfide. 1. Synthesis and Characterization of 1,2-Ethane-bis(trithiocarbonates) The reaction of 1,2-ethanedithiolates with carbon disulfide forms the corresponding 1,2-ethane-bis(trithiocarbonates). The compounds M₂[S₂C? SCH₂CH₂S? CS₂] with M = Li, Na, K, Rb, Cs, NH₄, Tl have been characterized with chemical methods as well as by means of electron absorption, infrared, nuclear magnetic resonance (¹H and ¹³C), and mass spectra.     

SIMS investigations of titanium profiles in LiNbO3 produced by ion beam mixing and diffusion

Summary In order to increase the refractive indices of LiNbO₃ just beneath the surface, i.e. to produce waveguides, titanium was incorporated into y-cut substrates by two different methods: Evaporated Ti layers were either diffused at 1000°C or mixed into the substrate with a 3 MeV Ti⁺ beam. Radiation damage caused by ion beam mixing was removed by epitaxial regrowth. The resulting Ti concentration profiles were investigated by means of secondary ion mass spectrometry. The diffused profiles could be fitted by half Gaussians with a diffusion constant ofD = 5.25 × 10^–17 m²/s at 1000°C. The ion beam mixed and annealed profiles show a non-zero slope at the surface and differ significantly from Gaussians.

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SIMS-Untersuchung von Titanprofilen in LiNbO₃ hergestellt durch Ionenstrahl-Mischung und Diffusion

     

The kinetics of chlorine evolution and reduction on glassy carbon in molten tetrachloroaluminate at 175°C

The chlorine electrode reaction on glassy carbon in sodium tetrachloroaluminate melt (AlCl₃+NaCl) with near equimolar compositions was investigated at 175°C with voltammetric techniques. The kinetic parameters (Tafel slope and exchange current density) measured as functions of chloride ion activity and partial pressure of chlorine, and the reaction orders with respect to Cl^? and Cl₂ have been collected extensively, being compared with the theoretical kinetic derivatives deduced from the rate equations solved under three different kinds of adsorption isotherms: Langmuir, non-activated Temkin and activated Temkin isotherms. All the evidence collected in this study indicates that the reaction mechanism for both evolution and dissolution of chlorine consists of a fast electron transfer (Cl^?→Cl_ad+e) followed (or preceded) by a slow Heyrovsky-type reaction (Cl^?+Cl_ad→Cl₂+e) on glassy carbon surfaces where the adsorbed intermediate obeys the activated Temkin isotherm. The exchange current density was found as 8.6±0.8 μA cm^?2 at 175°C in the melt of pCl=1.1 under an atmospheric pressure of Cl₂, and its electrode potential (E°_CΓ/Cl2) was determined as 2.182±0.005 V vs. Al.     

Ion-isotopic exchange reaction kinetics using organic base anion exchange resins Indion-102 and Indion GS-400

The present study deals with the kinetic study of iodide and bromide ion-isotopic exchange reactions in organic based anion exchange resins Indion-102 (nuclear grade) and Indion GS-400 (non-nuclear grade) using radiotracer isotopes. The resins in iodide and bromide form were equilibrated respectively with iodide and bromide ion solutions which were previously spiked with ¹³¹I and ⁸²Br radiotracer isotopes. For both bromide and iodide ion-isotopic exchange reactions, it was observed that the values of specific reaction rate increase with increase in ion concentration from 0.001 to 0.004 M at a constant temperature of 40.0°C. However, at constant ion concentration of 0.003 M, the specific reaction rate was observed to decrease with rise in temperature from 30.0 to 45.0°C. Also it was observed that for iodide ion-isotopic exchange reaction by using Indion-102 resin, the values of specific reaction rate, amount of iodide ion exchanged, initial rate of iodide ion exchange and logK _d were 0.258 min^?1, 0.492 mmol, 0.127 mmol/min and 19.2, respectively, which were higher than 0.208 min^?1, 0.416 mmol, 0.087 mmol/min and 17.6, respectively, obtained by using Indion GS-400 resin under identical experimental conditions of 40.0°C, 1.000 g of ion exchange resin and 0.003M labeled iodide ion solution. The same trend was observed for the two resins during bromide ion-isotopic exchange reaction. The overall results indicate that, under identical experimental conditions, Indion-102 resin shows higher performance than Indion GS-400 resin.     

An efficient halogen-free flame retardant for polyethylene: piperazinemodified ammonium polyphosphates with different structures

In this study, piperazine-modified ammonium polyphosphates(PA-APPs) with hierarchical structure were synthesized through ion exchange reaction. ~1H nuclear magnetic resonance(~1H-NMR), Fourier transform infrared spectra(FTIR), elemental analysis(EA), and inductively coupled plasma atomic emission spectroscopy(ICP-AES) confirmed that the PA-APPs with different structures were prepared successfully. Then these flame retardants were used alone as monocomponent intumescent flame retardant for low-density polyethylene(LDPE). Combustion tests demonstrated that the flameretardant efficiency of PA-APP containing about 7 wt% carbon(PA-APP_7) was significantly higher than that of the other PAAPPs with more or less carbon. The flame-retarded LDPE system with 30 wt% PA-APP_7 passed the UL-94 V-0 rating, and had the oxygen index(LOI) of 33.0%. Thermal analysis illustrated that the thermal decomposition behavior of PA-APP changed with incorporating different contents of PA. For all these PA-APPs, PA-APP_7 showed higher thermal stability than the other PA-APP flame retardants. All the experimental results proved that PA-APP_7 could reach the balance of an acid source, a blowing source, and a charring source as a mono-component intumescent flame retardant for LDPE. Further, it led to the formation of a compact intumescent char layer containing the structures of rich P―O―P, P―N―C, C=C, etc. during burning which in turn resulted in the excellent flame-retardant efficiency of PA-APP_7.     

Ion beam induced deposition of platinum carbon composite electrodes for combined atomic force microscopy–scanning electrochemical microscopy

In the present study, ion beam induced deposition (IBID) of platinum carbon (PtC) composite electrodes is evaluated for combined atomic force microscopy–scanning electrochemical microscopy (AFM–SECM) probes. After deposition, the PtC composite materials are post-treated using focused ion beam (FIB) milling to decrease the carbon content of the material. It is shown that this treatment leads to an improvement of electrode characteristics for selected analytes, including the oxidation of potassium hexacyanoferrate(II) trihydrate (Fe(CN)₆^4?) and hydrogen peroxide (H₂O₂). Moreover, the proposed approach is compatible with microfabricated AFM–SECM probes for increasing the AFM tip-integrated electroactive area while maintaining the geometric dimensions, which is important for imaging biosensor development.     

Decomposition of oxalic acid with nitric acid

Oxalic acid or oxalate is widely used as a precipitant and a detergent in the field of nuclear energy. The present work aimed at developing a method of decomposing oxalic acid with HNO₃ in the presence of Mn²⁺ ion. The use of Mn²⁺ ion as low as 10^?3 mol/l facilitated the complete decomposition of oxalic acid, and the acidity of the resulting solution became as low as 0.1 eq/1 under the optimum conditions. The decomposition of oxalic acid is a first order reaction and proceeds at temperatures above 80°C; the activation energy of the reaction is 18.6 kcal/mol. This decomposition method is applicable to the dissolution of an oxalate precipitate.