M.D. Ashbaugh

Determination of nitrogen using the 14N(α, p)17O nuclear reaction

Abstract A technique for quantifying nitrogen in thin films using the 14N(α, p)17O reaction is reported. An incident alpha particle beam with energy near 3.9 MeV is used and emitted protons are detected at a lab angle of 135°. A 15 μm Kapton foil is placed over the detector to stop elastically scattered alpha particles. A thin film containing a known areal density of nitrogen is used for calibration. We present relative yield data on protons from the 14N(α, p0)17)O reaction at 135° lab angle from 3.4 MeV to 4.0 MeV as well as an example of the application of this technique in determining nitrogen content in thin films. Possible interfering reactions, particularly 28Si(α, p)31, are also discussed.

Cross sections for 170.5° backscattering of 4He by the isotopes of boron for 4He energies between 1.0 and 3.3 MeV

Elastic scattering cross sections for 4He on both isotopes of boron have been measured at a laboratory angle of 170.5° in the energy range 1–3.3 MeV to an accuracy of about 7%. Self-supporting targets of natural boron (18μgcm2) and 99% enriched 10B (6μgcm2) were used. The scattering was observed to be Rutherford between 1 and 1.3 MeV for both isotopes. Previously unreported elastic scattering anomalies were observed in 10B near 1.5 and 1.65 MeV and in 11B near 1.5 and 2.05 MeV. Results above 2.1 MeV are compared to previous measurements; discrepancies of up to 50% are noted. The major features in the cross sections above 2.1 MeV are broad resonances near 2.4 MeV in 10B and near 2.6 MeV in 11B. The cross section is found to be smooth and approximately Rutherford for 11B in the energy range 2.2 to 2.5 MeV.

Quantification of beryllium in thin films using proton backscattering

Abstract The strong resonance in the 1H-9Be backscattering cross section near 1H laboratory energy 2525 keV has been used to determine 9Be areal densities in thin films with accuracies of about 6%. We report measured cross sections (for a 170.5° laboratory backscattering angle) for 1H on 9Be for 1H energies from 2400 to 2700 keV. The areal densities of the self-supporting Be foils used for the 1H-9Be measurements were determined from 4He-9Be backscattering measurements. We also report measured cross sections for 170.5° backscattering of 4He by 9Be for 4He laboratory energies of 500 to 4200 keV. Results of channeling measurements in epitaxial Be films on crystalline substrates are also discussed.

Determination of boron using the B(α,p)C nuclear reaction at incident energies near 3 MeV

Abstract A technique for determining boron content of thin films using the B(α,p)C reaction on both isotopes of boron is described. An incident alpha energy near 3 MeV is used and emitted protons are detected at 135° lab angle. A thin film containing a known areal density of boron is required for calibration. A comparison is made between this method and conventional elastic scattering of 4 He + ions for boron determination in thin films containing heavy elements or backings. We also present relative yield data on protons from the 10 B(α,p) 13 C and 11 B(α,p) 14 C reactinos at 135° lab angle between 1.4 and 3.3 MeV.

Ion-beam analysis of silicon carbide

Channeling and backscattering measurements with 3.8 MeV 4He analysis beams have been used to determine the CSi stoichiometric ratio in 100–200 nm SiCx(Hy) films deposited on (100) Si substrates by plasma-enhanced CVD using gas mixtures of CH4 and SiH4. The results show that both annealed and unannealed films are amorphous and allow determination of the CSi ratio to better than ±10% for 0.2 < x < 1.0. Film hydrogen content was determined by ERD with 3.5 MeV 4He analysis beams. In addition, potential problems associated with the use of the 4.265 MeV 4HeC resonance to quantify C in Si are discussed.

Cross section measurements for the (3He, p) nuclear reaction on B and N between 2 and 4 MeV

Abstract Cross section measurements have been made for several proton groups from the ( 3 He,p) nuclear reaction on boron and nitrogen. Incident energies between 2 and 4 MeV and angles of 90° and 135° were used. A 1.5 mm thick surface barrier detector, covered to stop elastically scattered 3 He ions, was used to detect the high energy protons from these reactions. The proton energy was as high as 20 MeV in the case of a boron target. We propose the use of these reactions for quantitative elemental areal density determination in thin film analyses.

Detection and depth profiling of 19F using a resonance at 2313 keV in the 19F(α,p)22Ne nuclear reaction

Abstract Cross section measurements are reported for the p0 and p1 proton groups from the 19F(α,p)22Ne nuclear reaction in the energy range 2150–2520 keV at a reaction angle of 135°. A narrow resonance at 2313 keV incident energy is shown to be useful in detecting and depth profiling 19F in thin films. Computer simulation is used to find F concentration profiles which are consistent with the measured reaction yield curves. Calculations of the depth resolution of this resonance and that of the 340 keV resonance in the 19F(p, αγ)16O reaction are compared for a specific target.

Use of the nuclear microprobe at the University of Arizona for the study of heavy metal deposition in rabbit renal tissue

Abstract Industrial wastes consigned to disposal sites frequently contain substantial amounts of heavy metals. We have successfully applied proton induced X-ray emission analysis (PIXE) in the conduct of heavy metal (Hg, Cd, Cr, As) toxicity studies using precision cut rabbit renal cortical slices. The large beam diameter (4000 μm) of the proton macroprobe at The University of Arizona Ion Beam Analysis facility allowed an overall concentration of the metal(s) of interest in the samples to be determined, but lacked the ability to resolve point concentrations in the tissue. The ability to locate these areas has now been made available to us with the addition of a rastering microprobe (μ-PIXE) to the facility. Studies now being conducted in our laboratory using this micro-technique include analysis of renal tissue taken from rabbits injected intraperitoneally with HgCl2, K2Cr2O7, and NaAsO2. The small beam size (3 μm) and the ability to raster this beam over areas of up to 125 μm × 125 μm has allowed regional mapping of endogenous and non-endogenous metal concentrations and revealed trends in heavy metal deposition in in vivo treated renal tissue, significantly increasing the amount of information obtained from these animal studies using PIXE alone. The combination of small beam size, high resolution, and multi-element detection makes μ-PIXE a powerful tool for investigating the impact of non-endogenous metals on the kidney.

The nuclear microprobe at the University of Arizona

Abstract A nuclear microprobe has been operational at the University of Arizona since early 1994. It utilizes a magnetic quadrupole doublet (model QL-300 from Microscope Associates, Inc.) with an 11 mm diameter aperture and lens lengths of 6 cm each. The magnetic pole tips are electrically insulated to enable electric rotational alignment and beam rastering by application of varying voltages to the pole tips. Ion beams are obtained from a 5.5 MV model CN, High Voltage Engineering Corp. Van de Graaff accelerator with a Penning type ion source. Present mininum beam spot size is about 2 μm obtained with a 4 MeV H2+ beam with a current of about 40 pA. To date, the instrument has been successfully used to map concentrations of Hg, Cr, and As in rabbit renal slices using PIXE.