Nuclear and atomic activation with heavy ion beams

Heavy ion activation has been studied as a method for determining hydrogen. The reactions used [e.g.¹H(⁷Li, n)⁷Be] are the “inverse” of well known reactions [e.g.⁷Li(p, n)⁷Be]. Nuclear activation parameters for the ion beams of interest (⁷Li²⁺,¹⁰B²⁺) have been studied. The analytical feasibility is demonstrated with the determination of hydrogen in titanium at the 100 and 30 ppm levels with relative precisions of 8 to 10%. Detection limits in titanium are in the 0.1 to 0.5 ppm range. Heavy ion bombardment is also accompanied by the emission of characteristic X-rays (“atomic” activation). The parameters governing X-ray emission and background production have been investigated. Experimental K and L X-ray yields from thick targets have been measured for many elements excited by Oⁿ⁺ beams of 0.5 to 7 MeV/amu and Kr⁷⁺ beams of 0.5 to 1 MeV/amu. The simultaneous determination of trace elements at levels of 10 to several 100 ppm in microsamples (∼10⁻⁵ g) is demonstrated on biological specimens. K and L X-ray yields and corresponding detection limits have also been measured with the⁷Li²⁺ and¹⁰B²⁺ beams used for the nuclear activation of hydrogen. With these beams (∼6 MeV/amu) simultaneous nuclear and atomic activation is possible, yielding an unusual multielement trace analysis capability covering hydrogen and medium and high Z elements.     

Possibilities of using simultaneous ion-induced nuclear and atomic activation for the characterization of hair

The possibility of a simultaneous determination of low and medium Z elements in hair in a single ion beam exposure was studied. Different ion beams, proton, deuteron,³He and¹⁸O, at velocities ranging from 2.7–6.9 MeV/amu were investigated. In this work,¹⁸ ₈O⁴⁺ beam was found to give the best experimental condition in terms of sensitivity and number of elements detected. The detection limits in a single hair ranged from 2.9·10⁻⁵ μg for Fe to 0.72 μg for H using this beam.     

Micro and surface analysis with fast heavy ions

The desorption of atomic and molecular species from surfaces bombarded by fast heavy ions (Z ? 20; E ? 0.5 MeV/amu) is attractive for surface and microscopic characterization. Only a low-intensity probe beam is needed, the escape depth of desorbed species is shallow (ca. 10 Å), and desorbed ions are efficiently detected with a time-of-flight mass spectrometer. Thus, particle-induced desorption mass spectrometry (PDMS) maintains sample integrity and charging effects are avoided. PDMS is useful for surface analysis of glasses and plastics by using californium-252 fission fragments for bombardment. Inorganic and organic surface constituents can be detected simultaneously; mass resolution is good. For lithium in glass, the detection limit is about 1 pg (ca. 100 μg g^?1. The PDMS technique can be combined with sequential ion etching for depth profiling. The feasibility of PDMS for microscopic analysis with a collimated 84-MeV Kr⁷⁺ beam (target diameter ca. 11 μm) is discussed.     

A comparison of modifications induced by Li<Superscript>3+</Superscript> and Ag<Superscript>8+</Superscript> ion beams irradiation in poly(lactide-<Emphasis Type="Italic">co</Emphasis>-glycolide) films

Poly(lactide-co-glycolide) (PLGA) films were irradiated by 180 MeV/amu Ag⁸⁺ ions and 50 MeV/amu Li³⁺ ions at different fluences of 5 × 10¹⁰, 5 × 10¹¹ and 1 × 10¹² ions/cm². Modifications of polymer films induced by the swift heavy ions (SHI) irradiation were studied by X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR) and UV–Vis spectroscopy. The dominant effect of the SHI beam irradiation is proposed to be chain scission which leads to breakage of polymer chains, followed by hydrogen abstraction. The results from FTIR spectroscopy showed that the intensity of all peaks of the irradiated samples decreased at high fluence of SHI, suggesting PLGA samples significantly degraded at high SHI fluence. The variation in optical band gap energy and Urbach energy with increasing fluence was calculated from UV–Vis spectroscopy and explained in terms of changes occurring in the polymer matrix. X-ray diffraction patterns also show appreciable changes in PLGA at high fluence. FESEM results revealed that the hydrophilicity of the PLGA surface increased with an increase in ion fluence. In this paper the optical, chemical and structural changes with different fluence rates are discussed.     

Analysis of Co and Cr dopants in epitaxial films of β-FeSi2 by ERDA, RBS, EDX and AES

Thin films of β-FeSi₂ doped with Co or Cr were grown on Si substrates by molecular beam epitaxy. The matrix components Fe and Si and the dopant were co-evaporated from three separately controlled sources. The dopant concentration was measured concurrently by ERDA, RBS, EDX and AES. Ion scattering spectrometry using heavy-ion beams of high energy (ERDA with 250 MeV ¹²⁹Xe, RBS with 15 MeV ¹⁴ N) proved to be most powerful in providing a high mass resolution (1 amu) and a low detection limit for Co and Cr (about 0.2 at %). Although the sensitivity of standard RBS (with 1.4 MeV ⁴He), EDX and AES is limited to a level of about 1 at% these methods allow to assess essential trends caused by variation of the deposition parameters.     

Fluence measurements applied to 5–20 MeV/amu ion beam dosimetry by simultaneous use of a total-absorption calorimeter and a Faraday cup

A Faraday cup was fabricated for measuring the beam current of a few tens MeV/amu ion beams of the TIARA AVF cyclotron. It has been applied as a beam monitor for studying the characteristics of film dosimeters that are well-established for high doses of ⁶⁰Co γ-rays and 1 to 10 MeV electrons. A total absorption calorimeter designed to measure energy fluence has also been tested for estimating the uncertainty in fluence measurement of 5–20 MeV/amu ion beams, by simultaneous use of the calorimeter and the Faraday cup in a broad uniform fluence field. The estimated fluence was evaluated on the basis of nominal particle energy values derived from the cyclotron acceleration parameters. The average ratio of the measured fluence values to the estimated values is 1.024, and the average precision is within ±2% at a 68% confidence level, for most of the ion beams with a range of kinetic energy per nucleon, 5–20 MeV/amu, at an integrated charge above 5 nC/cm².     

Ta,Au and Th L X-ray energy shifts induced by 0.6, 1.2, 2.4 and 4 MeV/nucleon Kr ions

The L X-ray spectra of Ta, Au and Th induced by 0.6 to 4 MeV/nucleon (MeV/n) ⁸⁴Kr ions have been studied by means of a LiF(100) equipped crystal spectrometer with an overall resolution of 30 eV at 8.146 keV. The mean energy shifts of the main lines have been measured with accuracies ranging from 5 eV for well separated lines, to 30 eV for poorly resolved lines. Mean energy shifts per M and N spectator electron vacancies were deduced and compared with predictions of different models. The mean number of these vacancies at the various beam energies were estimated. Diagram lines were also observed and assigned to the internal conversion of transition energies between nuclear Coulomb excited levels. In the case of the Lα lines of Ta and Au and at the lower beam energies (0.6 and 1.2 MeV/n) the full width at half maximum of these lines was used to deconvolute the shifted peaks in the individual corresponding satellite lines.     

The use of ion-induced x-rays for spectrochemical analysis

The application of ion-induced x-rays to spectrochemical analysis was examined by means of a dispersive method with a flat crystal and a 200-kV ion accelerator. For x-rays of longer wavelength than 10 Å, x-ray count rates of the order of 10⁴–10⁵ c.p.s. were obtained; the use of heavy ions such as Kr⁺, Ne⁺ and O⁺ was shown to be effective for x-rays shorter than about 30 Å, while protons were more efficient for longer wavelengths. X-Ray excitation efficiencies are almost independent of the atomic shell with which the x-rays are associated and are dependent on wavelength only, indicating that almost all elements can yield K, L or M x-rays of considerable intensity. The x-ray excitation method by proton and heavy ion bombardment was applied to the determination of some light elements, F, O, N and Be. Detection limits of 10 p.p.m. could be readily achieved for these elements.     

L-shell X-ray production cross section measured by heavy ion impact on selected rare earth elements

The production cross sections of L-shell X-ray of some rare earth elements have been measured by collision of ¹²C⁴⁺ and ¹⁶O⁴⁺ ions of 0.5 to 0.75 MeV/amu. The results were compared with experimental data of other authors and with theoretical predictions gained by the ECPSSR and ECPSSR plus multiple ionization (ECPSSR+MI) models. For atomic parameters (fluorescence yields and probabilities for Coster-Kronig transitions) the role of several databases were studied. The ECPSSR theory underestimates cross sections when compared with experimental results obtained in the present work, but ECPSSR+MI has a better agreement with the experimental data. This revised version was published online in July 2006 with corrections to the Cover Date.     

Contribution a l'etude de la determination de Be,B, C,N, O et F par activation au moyen de p,d,3He et α

The activation of these elements, homogeneously contained in a medium thicker than the path length, of slowing-down capacity close to that of aluminium, was determined as a function of energy by irradiating standards with p, d,³He and α particles of energies between: 5 and 15 MeV for protons, 5 and 20 MeV for deuterons and³He particles, 25 and 42 MeV for α particles. The detection sensitivities intrinsically possible in these energy ranges are deduced from the curves obtained. The results apply to all materials through a simple relationship taking into account the path lengths. They may be used in particular to foresee the possibilities offered by activation with these charged particles, from the viewpoint of sensitivity, when the samples to be analysed are irradiated with a beam of given intensity and energy lying between the above limits.     

Measurements of relative thick target yields for PIGE analysis on light elements in the proton energy interval 2.4–4.2 MeV

In order to extend the energy range of the systematic investigation on relative thick target yields performed by ANTTILA et al² for 1E_p2.4 MeV bombarding energies, gamma spectra and yield data are presented for elements Z=3–9, 11–17, 19–21 in the energy range 2.4E_p4.2 MeV and the results are discussed from the point of view of PIGE analysis.     

Laboratory and synchrotron radiation total-reflection X-ray fluorescence: new perspectives in detection limits and data analysis

Having established detection limits for transition elements exceeding current requirements of the semiconductor industry, our recent efforts at the Stanford Synchrotron Radiation Laboratory (SSRL) have focused on the improvement of the detection sensitivity for light elements such as Al. Data analysis is particularly challenging for Al, due to the presence of the neighboring Si signal from the substrate. Detection limits can be significantly improved by tuning the excitation energy below the Si–K absorption edge. For conventional TXRF systems this can be done by using a W–Mα fluorescence line (1.78 keV) for excitation. At a synchrotron radiation facility energy tunability is available. However, in both cases this results in a substantial increase in background due to resonant X-ray Raman scattering. This scattering dominates the background under the Al Kα fluorescence line, and consequently limits the achievable sensitivity for the detection of Al surface contaminants. In particular, we find that for a precise determination of the achievable sensitivity, the specific shape of the continuous Raman background must be taken into account in the data analysis. The data deconvolution presented here opens a new perspective for conventional TXRF systems to mitigate this background limitation. This results in a minimum detection limit of 2.4×10⁹ atoms/cm² for Al. Based on these results it will also be demonstrated that by improving the detector resolution, the minimum detection limit can be improved significantly. For a detector resolution of 15 eV as predicted for novel superconducting tunnel junction detectors, an improvement in minimum detection limit of approximately a factor of 3 can be estimated.     

Atomic and molecular impurities in4He clusters

Recoil-ion charge distributions produced in single collisions of 8 MeV/u Kr¹³⁺ and Kr³²⁺ projectiles with Xe atoms have been measured using time-of-flight spectroscopy. The post-collision charge states of the projectile ions were determined by magnetic dispersion onto a position sensitive microchannel plate detector. The recoil-ion distributions for ionization accompanied by electron loss from Kr¹³⁺ projectiles were bell-shaped with averages that ranged from 7.4 for 1-electron loss to 13.9 for 5-electron loss. The recoil-ion distributions for ionization accompanied by electron capture to Kr³²⁺ projectiles were also bell-shaped, but had much higher average charges that ranged from 20.4 for 1-electron capture to 28.5 for 4-electron capture. The large difference in the average charges produced in the two types of collisions is mainly attributable to charge magnification by Auger decay. A simple model quantitatively explains the variation of the capture-ionization charge distribution width and average charge as a function of the number of captured electrons.     

Preparation of a radioactive multitracer solution from iron foil irradiated by 80 MeV/nucleon16O ions

Iron foil was irradiated with an 80 MeV/nucleon¹⁶O-ion beam. The foil was dissolved in hydrochloric acid, and Fe²⁺ in the solution was oxidized to Fe³⁺ with hydrogen peroxide. The solution was diluted to 6M in HCl and was passed through an anion exchange column. Washing with 6M HCl yielded a carrier- and salt-free multitracer solution covering radioactive nuclides of elements from sodium to manganese.     

Charged particle activation of medium Z elements

A survey has been made on the application of charged particle activation analysis for the detection of traces of medium Z elements (40≤Z≤58, 72, 74) using protons and deuterons of 20 MeV,³He and⁴He ions of 40 MeV. The product nuclides considered were γ-ray emitting radioisotopes with half lives ranging from 10 min to 3 days. Based on the thick target yields obtained, proton activation was found to provide an optimum compromise between sensitivity and selectivity.     

Determination de C,N, O,F et de quelques autres elements par activation au moyen des photons gamma

The (γ, n) activation curves for 17 elements were determined as a function of energy between 25 and 42 MeV. From these are deduced the detection sensitivities intrinsically possible for an average beam intensity of 100 μA. Our experimental results are compared with values calculated byG. J. Lutz. The activation curves relative to certain competitive nuclear reactions on N, O and Na, liable to interfere in the measurements of C, N and F, were also determined. It is shown that the relative importance of these competitive nuclear reactions decreases rapidly for energies below 30 MeV and becomes practically negligible at 25 MeV.      

The determination of carbon,nitrogen and oxygen in gases by neutron time-of-flight spectrometry

Carbon, nitrogen and oxygen were determined in gases by time-of-flight spectrometry of prompt neutrons from the respective reactions¹²C(d, n)¹³N,¹⁴N(d, n)¹⁵O and¹⁶O(d, n)¹⁷F, produced by a pulsed beam of deuterons of 2 MeV (for nitrogen) or 3 MeV. The analysis is non-destructive and requires about 15 min. per sample. The relative standard deviation for all three elements was about ±3%. Detection limits, using a total irradiation current of 20 millicoulombs, for carbon, nitrogen and oxygen, respectively, were 6·10⁻⁸ g, 2·10⁻⁷ g and 1.7·10⁻⁷ g per cm² cross-sectional area of irradiating beam.     

The electron-impact ionization of Ar and Kr revisited: a critical analysis of double-to-single ionization cross section ratio measurements using the fast-atom-beam technique

We report new measurements of the absolute electron-impact double ionization cross sections for Ar and Kr and of the ratios of double-to-single ionization for impact energies from threshold to 200 eV using the crossed electron-beam — fast-atom-beam technique. The work was motivated by the recently highlighted spread of about 30% in the Ar²⁺/Ar⁺ ionization cross section ratios obtained by several groups using different experimental techniques. Such a spread is inconsistent with statistical uncertainties of typically 3% or less that were quoted for the various reported ratios. A similar situation exists for Kr where the spread among the recently published Kr²⁺/Kr⁺ ionization cross section ratios is about 15%. We made an attempt to identify all potential systematic errors inherent to the fast-beam technique that could affect the measurement of cross section ratios with special emphasis on those systematic errors that could influence the detection of singly and doubly charged product ions differently. We found Ar²⁺/Ar⁺ and Kr²⁺/Kr⁺ cross section ratios of, respectively 0.066 ±0.007 and 0.087 ±0.008 at 100 eV which confirm earlier measurements using the same experimental technique. The error limits on cross sections ratios measured in our fast-beam apparatus were determined to be at least ±9% for cross section ratios of multiple-to-single ionization for the same target atom and at least ±10% for ratios of single ionization cross sections for different target species. Our error limits are dominated by systematic uncertainties of the apparatus which do not cancel when cross section ratios are measured, since the ratios are obtained under similar, but not identical experimental conditions.     

Studies on the long-term stabilities of the background of radionuclides in inductively coupled plasma mass spectrometry (ICP-MS)

The long-term stabilities of the ICP-MS background of nine radionuclides are studied, of which the signals are partially superimposed by polyatomic interferences or affected from carry-over and memory effects. The background generated by the ICP flame, by two pure waters, and by nitric acid (2% v/v) was investigated in detail. A minimum of 50 measurement points was used for each long-term investigation. The detection limits of the radionuclides of the masses 90 amu (⁹⁰Sr: 30 Bq/mL), 99 amu (⁹⁹Tc: 4 mBq/mL), 238 amu (²³⁸U: 10 nBq/mL), and 244 amu (²⁴⁴Pu: 0.6 Bq/mL) are calculated from the mean standard deviation of the background signals. For all nine radioisotopes, the calculated detection limits are between 0.8 and 6 pg/mL. While the detection limit of the mass 90 amu is blank limited, those of the mass 99 amu and the actinides are totally uneffected by the blank solutions. The detection limits are compared with those given in literature.     

Field-evaporation mass spectroscopy applied to crown ether complexes with alkali and alkaline-earth metals

Field evaporation from solution has been used to detect crown-ether 15K5 and 18K6 coordination compounds formed with Na⁺, K⁺, Cs⁺, Ba²⁺ and Ca²⁺ in aqueous solution, both hydrated and unhydrated; the Ca²⁺·18K6·(H₂O)_n (n=0, 1, 2,...) compounds have been observed before. 18K6 present in the solution greatly increases the yields of 18K6 compounds with the dissociation products from Ba(NO₃)₂. The detection limits for 15K5 and 18K6 combined with Na⁺, K⁺, and Cs⁺ are approximately the same at 10^–7 g.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 2, pp. 239–242, March–April 1988.