On the ion beam stopping power dependence of transient magnetic fields in Fe- and Gd-hosts

Ion-beam induced attenuations of transient magnetic fields have been further studied in measurements on high-velocity²⁴Mg- and²⁸Si-ions as well as low-velocity⁴⁸Ti-ions using energetic beams of Ti- and Br-ions. Further evidence for the stopping power dependence of the attenuations is found; more data in the threshold region of Fe-host support earlier observations. In Gd-host the attenuations are again weaker pronounced than in Fe in accordance with previous data.     

Vicinage effects in the stopping power of H 3 + beams in amorphous carbon

The stopping power of H ₃ ⁺ molecular beams incident on amorphous carbon foils is analyzed as a function of the orientation of the molecule relative to its direction of motion. The electronic stopping power was calculated within the dielectric formalism, taking into account the dynamics of the Coulomb repulsion among the molecular partners. At intermediate velocities, ν ? 2 a.u., the stopping ratio for the perpendicular orientation is greater than for the parallel one, while the opposite behaviour is shown for higher velocities. The stopping ratio for randomly oriented H ₃ ⁺ molecules was evaluated for different target thicknesses, resulting in larger values for the thinner targets and the higher energies. Comparison of our results with available experimental data shows a reasonable agreement.     

ESR study for ion beam induced phenomena in poly (tetrafluoroethylene-co-hexafluoropropylene) (FEP)

Trapped radicals induced in poly (tetrafluoroethylene-co-hexafluoropropylene) (FEP) were observed by X-band electron spin resonance (ESR) spectroscopy at room temperature (RT) under atmospheric field after an irradiation with various kinds of high energy ion beams (6 MeV/u). The irradiation was carried out to a stacked FEP films under vacuum (<4E?4 Pa) at RT with various fluences from 1.0×10⁹ to 1.0×10¹¹ ions/cm². All ESR spectra indicated an existence of peroxy radicals in each of the FEP films without any relation to a kind of ion and a penetration depth. Obtained depth profiles of radical concentrations induced with each ion beam almost correspond to those of stopping power. The trapped radical concentrations were strongly dependent on stopping power. It was found that G-value of trapped radicals by ion beam irradiation was decreased with increasing a stopping power, and was less than the case of gamma-rays irradiation.     

Stopping power and energy loss straggling of thin Formvar foil for 0.3–2.7 MeV protons and alpha particles

Stopping power and energy loss straggling data for protons (¹H⁺) and alpha particles (⁴He⁺) crossing Formvar thin polymeric foils (thickness of ～0.3 μm) have been measured in the energy range (0.3–2.7) MeV by using the indirect transmission technique. The determined stopping power data were compared to SRIM-2010, PSTAR or ASTAR calculation codes and then analyzed in term of the modified Bethe–Bloch theory to extract the target mean excitation and ionization potential 〈I〉. A resulting value of 〈I〉≈(69.2±1.8) eV was deduced from proton stopping data. The measured straggling data were corrected from surface roughness effects due to target thickness inhomogeneity observed by the atomic force microscopy (AFM) technique. The obtained data were then compared to derived straggling values by Bohr's and Bethe–Livingston's classical theories or by Yang's empirical formula. A deviation of ～40%–80% from the Bohr's straggling value has been observed for all reported energies, suggesting that the Bohr theory cannot be correctly applied to describe the electronic energy loss straggling process with the used low thickness of Formvar foil. The inner-shell contribution of target electrons to energy loss process is also advanced to explain the observed deviation from experiment in case of He⁺ ions. Finally, the reliability of Bragg's additivity rule was discussed in case of stopping power and straggling results.     

Round-robin test of medium-energy ion scattering for quantitative depth profiling of ultrathin HfO2/SiO2/Si films

Medium-energy ion scattering (MEIS) has been used for quantitative depth profiling with single atomic layer resolution to determine the composition, thickness, and interface structure of ultrathin films and nanoparticles. To assure the consistency of the MEIS analysis, an international round-robin test (RRT) with nominally 1-, 3-, 5-, and 7-nm thick HfO₂ films was conducted among 12 institutions. The measurements were performed at each participating laboratory under their own conditions, and the collected data were analyzed. For the data analysis, the Moliere potential, the stopping and range of ions in matter (SRIM) 95 and new fitted electronic stopping power and the Chu straggling were used. For analyzing the MEIS data from the magnetic sector and electrostatic analyzers, the neutralization corrections of Marion and Young for 100-keV H⁺ and He⁺ ions and of Armstrong for 400- to 500-keV He⁺ ions were used. The standard deviations were 5.3% for the composition, 15.3% for the thickness, and 13.3% for the Hf content, and they were improved to 7.3%, 4.5%, and 7.0% by using refitted electronic stopping powers based on the experimental data. Hence, this study suggests that correct electronic stopping powers are critical for quantitative MEIS analysis.     

Positron annihilation and ion beam analysis of ion-bombardment-induced hydrogen release and oxidation of ultra high molecular weight polyethylene

Ultra high molecular weight polyethylene was bombarded with He⁺ and Ar⁺ ions to fluences ranging from 10¹³ to 2×10¹⁶ ions/cm². Rutherford backscattering and nuclear reaction analysis were applied to study mechanism of oxygen uptake and hydrogen release induced by ion beam bombardment. The influence of ion bombardment on positron annihilation lifetime parameters is also discussed. Hydrogen release was observed with increasing ion dose and was correlated to the ion stopping power. An important effect observed, was the rapid oxidation of samples after exposure to air.     

Search for molecular effects in range corrections: Lithium determination by proton bombardment

Three different proton-induced reactions were used to analyze 19 pure lithium compounds of known composition. Prompt alpha-particles were measured from the reaction⁷Li(p, )⁴He at E_p=4.5 MeV and prompt gamma-rays of 429 and 479 keV from the ractions⁷Li(p,n)⁷Be and⁷Li(p,p)⁷Li, respectively, at E_p=4.5 MeV. Elemental stopping powers were calculated from tables and used to compute the stopping power of the target matrices by Bragg's Law. Apparent discrepancies in the measured yield could point to deviations from Bragg's Law and hence to molecular effects. The maximum value for any molecular effect was found to be <5.5%.     

Stopping power effects in the determination of14N by a resonance reaction

The applicability of the¹⁴N(p,p’ γ₁)¹⁴N nuclear reaction in the determination of the absolute abundance of¹⁴N, with a 2% uncertainty, was demonstrated at 4.3 MeV bombarding energy. The fact that almost all of the thick target γ-ray yield resulted from a resonance at Ep=4.0 MeV allowed to consider the necessary stopping-power corrections only at the energy of that resonance. Alternatively, the method was used to obtain the stopping power of 4.0 MeV protons in complex biological materials. Supported in part by the International Atomic Energy Agency, Vienna, Austria.     

Delta-electron emission in fast heavy ion — atom collisions: observations of new phenomena and breakdown of common scaling laws

Double differential cross sections for the emission of Delta-electrons have been measured in fast uranium-rare gas collisions. The well-known Binary Encounter peak reveals unexpected structures for certain observation angles and its intensity increases towards smaller angles, which is in contradiction to results and scaling laws obtained by experiments with light ion impact. The observed dependencies are fairly well described by recent calculations in the framework of IA and CTMC. From systematic experimental as well as theoretical studies we can derive that the potential of the partially stripped projectile ion gives rise to rainbow and glory scattering of the target electron in the field of the projectile. The rainbow scattering is observed in the laboratory frame as pronounced interference structures, whereas the glory scattering is responsible for the steep increase of the cross sections for binary-encounter electrons towards small laboratory ejection angles. The observed effects have a dramatic influence on the commonq ² scaling laws derived from experiments with light ions. Furthermore, since the binary-encounter electrons ejected at forward angles have approximately twice the projectile velocity, these new phenomena have an important influence on the electronic stopping power of heavy ions and therefore have to be taken into account for the investigation of radiation damage by these ions e.g. in biological matter.     

Muon transfer induced by collisional excitation of helium muonide Heμ+ after muon catalyzed fusionafter muon catalyzed fusion

Possibility of negative muon transfer from helium muonide He⁺ to T /or D/ through collisional excitation after muon catalyzed fusion has been pointed out. The transfer process depends on the efficiency of collisional excitation of He⁺ in the medium of tritium or deuterium. It is argued that tritium has larger nuclear stopping power and better excitation efficiency than deuterium. This effect is in the same direction as the tritium concentration dependence of muon loss probability in recent experimental work.     

Investigation of 500 keV Si ion induced surface structuring of Ni and Ti for enhancement of field emission properties

The present paper reports the investigation of surface morphology, elemental composition, phase changes and field emission properties of Si ion irradiated nickel (Ni) and titanium (Ti). The Ni and Ti targets have been irradiated with 500 keV Si ions generated by Pelletron accelerator at various fluences ranging from 6.9 × 10¹³ to 77.1 × 10¹³ ions/cm². Stopping range of ions in matter analysis revealed higher values of electronic stopping and sputtering yield for Ni as compared with Ti. For both irradiated metals, electronic energy loss dominant over the nuclear stopping. The growth of induced surface structures have been analysed by using field emission scanning electron microscopy (FESEM) analysis. In case of Ni, as the ion fluence increases from 6.9 × 10¹³ to 65.8 × 10¹³ ions/cm², the formation of spherical particulates, agglomers and sputtering is observed. Although in the case of Ti, with the increase of Si ion fluence from 11.6 × 10¹³ to 77.1 × 10¹³ ions/cm², the formation of irregular-shaped particulates along with crater and sputtered channels is observed. X-ray diffraction (XRD) analysis shows that no new phase is identified. However, a significant increase in peak intensity is observed with increasing ion fluence. The variation in crystallite size and dislocation line density is also observed as a function of Si ion fluence. Fourier transform infrared spectroscopy analysis shows that no bands are formed after the Si ion irradiation. Field emission properties of ion-structured Ni and Ti are well correlated with the growth of surface structures observed by SEM and dislocation line density evaluated by XRD analysis.     

Prompt nuclear analysis in thick samples with charged particles: The validity of Bragg’s law for range correction

The determination of fluorine in the fluorides of 31 elements by prompt analysis using the reactions (α, p₀), (α, α¹), (α, n₁γ) and (α, p₁γ) on¹⁹F was carried out in a search for discrepancies that could point to molecular effects in range corrections. Data for each reaction were normalised and normalisation factors were compared. The results for each compound were in good agreement, but intercomparison showed that the accuracy of stopping power data and the applicability of Bragg’s Law were acceptable within ±8%.     

Target element dependence in the elastic and inelastic energy loss of fast heavy ions

The target atomic number dependence of elastic and inelastic stopping power has been investigated by using theoretical stopping power formulations from literature. The stopping powers for target elements with atomic numbers from 3 to 92 are calculated on the basis of the model of Montenegro et al. and the nuclear stopping power is calculated using the formulation of Wilson et al.. The target atomic number dependence of the electronic and nuclear stopping power is examined for some light and heavy projectiles by comparing the stopping powers for all considered targets. It is observed that there is a strong target atomic number oscillation for helium, nickel and silver ions in nuclear and electronic stopping as a result of varying densities of neighboring elements. We have also determined the target materials, which apply a maximum total stopping force for some incident ions.     

Stopping power calculations of molecules for swift projectiles

Electronic stopping cross-section of compounds is calculated by considering velocity-dependent projectile and target electronic structure, and applying the Bragg addition rule. For velocity dependencies of projectile and target, we used previously developed stopping power formula by Tufan et al. In this work, we used two different screening functions. We calculated the electronic stopping cross-section of Al₂O₃, CO₂, and SiO₂ for O and Si ions. We compared our results with the other theoretical calculations and found 4–8% deviation.     

Inelastic scattering and energy loss of swift electron beams in biologically relevant materials

The inelastic mean free path and the stopping power of swift electrons in relevant biomaterials, such as liquid water, DNA, protein, lipid, carotene, sugar, and ice are calculated in the framework of the dielectric formalism. The Mermin Energy Loss Function – Generalized Oscillator Strength model is used to determine the energy loss function of these materials for arbitrary energy and momentum transfer using electron energy‐loss spectroscopy data as input. To ensure the consistency of the model, efforts are made so that both the Kramers–Kronig and f‐sum rules are fulfilled to better than 2%. Our findings indicate sizeable differences in the inelastic mean free path and stopping power among these biomaterials for low‐energy electrons. For example, at 100‐eV electron energy, the inelastic mean free path in protein is 25% smaller than for water and around 10% smaller than for the other biomaterials. The stopping power values of protein, DNA, and sugar are rather similar but 20% larger than for water. Taking into account these results, we conclude that electron interactions with living tissues at the nanometric scale cannot be reliably described using only liquid water as the surrogate of the biological target. Copyright © 2016 John Wiley & Sons, Ltd.     

Remarks on stopping power: Its connections with particle transport and with the electronic structure of matter

This article presents remarks on the meaning of stopping power and of its magnitude. More precisely, the first set of remarks concerns the connection of stopping power with elements of particle-transport theory, which describes particle transport and its consequences in full detail, including its stochastic aspects. The second set of remarks concerns the magnitude of the stopping power of a material and its relation with the material's electronic structure and other properties. © 1996 John Wiley & Sons, Inc.     

Energy loss of heavy ions in a dense hydrogen plasma

The energy loss of heavy ions with an energy of 1.4 MeV/u in a hydrogen plasma has been measured. A 20 cm longz-pinch has been used as plasma target. Our data show a strong enhancement of the stopping power of the plasma compared to that of a cold gas with equal density. The results completely confirm the predictions of the standard stopping power model.     

A method for charged-particle activation analysis and its application to fluorine determination by the19F(p, αγ)16O reaction

A simple method for calculating the sensitivity for detecting a nuclide distributed uniformly in any given matrix through charged particle activation is described. This method takes into account the actual values of the reaction cross section at different energies as the beam traverses through a thick target and the corresponding stopping power values. The detection sensitivity for fluorine in a number of matrices through the¹⁹F(p, αγ)¹⁶O reaction have been calculated as a function of the energy from threshold to 4.16 MeV using this method and the sensitivity curves plotted. The sensitivity values (dps/ppm/μA) for a thick or thin target and even for a layer of known thickness at a particular depth within a sample can be directly read from these curves for known bombarding conditions. The comparator methods for charged particle activation analysis of RICCI¹ and of CHAUDHRI,² especially when the matrices of the sample and standard are different, have been compared in the case of F determination through the¹⁹F(p, αγ)¹⁶O reaction. It has been found that the errors are reduced by almost a factor of two when the latter method is used compared to the former one. The fluorine concentration in animal bones and teeth, apatite crystal, and rocks have been determined through the¹⁹F(p, αγ)¹⁶O reaction using the Melbourne University Pelletron.     

Zone trapping/merging zones in flow analysis: a novel approach for rapid assays involving relatively slow chemical reactions

A novel strategy for accomplishing zone trapping in flow analysis is proposed. The sample and the reagent solutions are simultaneously inserted into convergent carrier streams and the established zones merge together before reaching the detector, where the most concentrated portion of the entire sample zone is trapped. The main characteristics, potentialities and limitations of the strategy were critically evaluated in relation to an analogous flow system with zone stopping. When applied to the spectrophotometric determination of nitrite in river waters, the main figures of merit were maintained, exception made for the sampling frequency which was calculated as 189 h⁻¹, about 32% higher relatively to the analogous system with zone stopping. The sample inserted volume can be increased up to 1.0 mL without affecting sampling frequency and no problems with pump heating or malfunctions were noted after 8-h operation of the system. In contrast to zone stopping, only a small portion of the sample zone is halted with zone trapping, leading to these beneficial effects.     

Einige Aspekte der Quantitativen Röntgenemissionsanalyse Leichter Elemente bei Anregung Mit Schweren Teilchen

The aim of the paper is the simplification of calibration procedures in the investigation of multi-element-systems by calculating calibration curves. This requires, as well as taking into account the measuring geometry and the detector properties, above all the calculation of the number of the characteristic X-rays emitted by the sample per incident particle. For the calculation of the thick target yield a computer programme has been developed which makes possible a simple exchange of subroutines describing the stopping power of the sample, the cross-section of K-shell ionization, the fluorescence yield and the matrix absorption for the resulting K-X-rays of the elements contained in the sample. The agreement between experiment and calculation is discussed, when various approximations for the functions mentioned are used, as well as the possible influence of the grain size and surface roughness of the samples on the measurements, on which the calculations are based.