G. Kajrys

Alignment processes and shape variations in 184Pt

Abstract High-spin states in the transitional nucleus 184Pt were populated via the reactions 154Sm(34S, 4n)184Pt and 172Yb(16O, 4n)184Pt. The yrast band was extended up to I = 28 ħ and six new side bands built on both neutron and proton quasiparticle configurations were observed. Shell correction-type calculations indicate variations of the nuclear shape in different bands, especially as a result of band crossings due to the process of angular momentum alignment. Comparison of the band characteristics are made between 184Pt and eight adjacent nuclei. The pattern of band crossings in these nine nuclei is considered from the viewpoint of blocking comparisons and of theoretical calculations. The competition between low-frequency vi 13 2 and πh 9 2 band crossings is discussed.

Characterization of Trace Elemental Pollutants in Urban Snow Using Proton Induced X-ray Emission and Instrumental Neutron Activation Analysis

Abstract Proton-induced X-ray emission (PIXE) and instrumental neutron activation analysis (INAA) methods have been employed to determine trace elemental pollutants in urban snow collected mostly from the island of Montreal and some from Toronto. The use of small pore filters, 0.40μm, enabled a distinction to be made between soluble and insoluble particulate fractions. Results for those elements, including heavy metals, that filtered through the 0.40 /an pore filters gave an indication of their bioavailability and potentially toxic actions. A total of twenty-five trace elements (Na, Mg, Al, P, S, CI, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Mo, Cd and Pb) were obtained in the soluble snow portion with detection limits between 0.2ng/g and 147ng/g. Twenty-eight elements (Na, Mg, Al, P, S, CI, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Cd, Sb, La, Sm and Pb) were analyzed with detection limits between 3 μg/g and 720 μ/g in the insoluble particulate matter. INAA pro...

Total soluble and insoluble sulfur concentrations in urban snow

Total soluble and insoluble sulfur concentrations in urban snow collected around the island of Montreal were measured by using proton-induced X-ray emission (PIXE) techniques. Cobalt was chosen as the internal standard for the soluble fractions while aluminum, whose concentration was determined by instrumental neutron activation analysis (NIAA), was used for the particulate matter. Feasibility experiments using induced coupled plasma (ICP) spectrometry were also employed to determine soluble sulfur concentration in snow collected from several inner-city Toronto sites and from Sault St. Marie, Ontario. The use of of a 0.40-..mu..m Nuclepore filter revealed that between 85% and 90% of the sulfur was water soluble. The average total concentration was about 1500 ..mu..g os S/L of snow. Total annual bulk deposition was estimated to be 1300 mg/(m/sup 2/ year) for the soluble portion and 200 mg/(m/sup 2/ year) for the particulate matter. Enrichment factor values strongly suggested that sulfur arises predominantly from anthropogenic sources. Element pair correlations with manganese and the possible role of manganese as a catalytic oxidant of sulfur are discussed.

The microbeam facility at the University of Montreal

Abstract The 4.5 MV Dynamitron injector for our 6 MV Tandem is now used to provide a proton beam for a dedicated FIXE, RBS, PIGE microbeam facility. An electrostatic quadrupole triplet lens produces a beam spot of 20 μm diameter. The target chamber, which is a modified 4 in. Dependex cross, houses an electron flood gun, and SB detectors. The targets are mounted on a stepper motor controlled HPT 040 micromanipulator. A 30 mm2 Si(Li) detector (FWHM = 154 eV at 5.9 keV) is used for PIXE measurements. Data on the impurities found in “water trees”, which are associated with breakdown in electrical cables, will be presented.

Damage induced in GaAs by high-energy Be, Si and Se implantation

Abstract Semi-insulating {100} GaAs wafers have been implanted with 3 MeV 9 Be 2+ , 7 MeV 28 Si 2+ and 8 MeV 80 Se 2+ ions to total doses ranging from 10 14 to 10 16 ions/cm 2 and the resulting damage has been profiled by channeling/Rutherford backscattering (RBS) spectroscopy with 5 MeV α-particles. The effect of different rapid thermal annealing (RTA) conditions has been studied. While it was possible to recover most of the original crystal structure, RTA processing could not eliminate a thin layer of secondary defects near the end of the projected range of the implanted ions. The density of defects after annealing has been calculated in the framework of a simple model and the depth profiles obtained by channeling/RBS have been compared with the profiles of chemically free as obtained by XPS, the secondary defects observed by XTEM and the vacancy distributions calculated by TRIM.

A channeling/RBS study of SOI structures by SIMOX using MeV ions

Abstract Silicon-on-insulator (SOI) structures, formed by implanting n-type 〈100〉 silicon substrates with 3 × 1017, 6 × 1017 and 8 × 1017 O2+ ions cm−2 at 6 MeV, have been characterized by channeling/Rutherford backscattering spectroscopy (RBS). An amorphous buried layer was formed about 4 μm from the surface. In the as-implanted samples, the Si overlayer was damaged from the surface to the buried layer, but still monocrystalline. After annealing at 1300°C for 2 h, the crystal structure is restored from the surface to a depth around 3.2 μm. RBS spectra showed that samples annealed at 1300°C for 6 h exhibited narrower oxygen distributions than those annealed at 1240°C for longer time (13 h). For the largest dose (8 × 1017 ions cm−2), a nearly stoichiometric oxide layer was formed after annealing at 1300°C for 6 h.

Cross-section measurements for 7Li + 11B AND 7Li + 13C reactions at low energies

Abstract The 7 Li + 11 B and 7 Li + 13 C reactions have been studied at incident energies below and around the Coulomb barrier, by measurement of the cross sections for the characteristic γ-rays emitted by the residual nuclei. The nα, αα and np emission channels are found to be enhanced with respect to the statistical compound nucleus predictions, while the nn and single-particle emission channels are not enhanced. An unusual energy dependence is observed for the 7 Li + 11 B → nn 16 O 7.12 MeV channel cross section, suggesting the existence of a broad resonance.

Determination by Raman scattering of the in depth damage profile in high energy ion implantation

Abstract Ion implanted GaAs samples have been chemically etched to form a small angle beveled surface. First order Raman spectroscopy has been performed along the bevel of as-implanted samples bombarded with 2.3 MeV Be and 10.9 MeV Se ions. The phonon confinement interpretation [H. Richter et al., Solid State Commun. 39 (1981) 625] has been employed to fit the spectra and obtain the damage distributions. Comparisons with X-ray diffraction (XRD) and RBS-channeling (RBS) measurements show good agreement with regard to the basic shape and depth of the profiles. The Be-implanted sample shows a damaged layer at a depth of 2.5 to 4 μm while the Se implant shows a much wider damaged layer at a depth between 1 and 3.5 μm.

Cross-section measurements for the 9Be + 9Be, 7Ll +11B and α + 14C reactions at low energies☆

Abstract The 9Be + 9Be, 7Li+11B and α +14C reactions, leading to the 18O compound state in the excitation energy range between 25 and 31 MeV, have been studied by measurement of the cross sections for the characteristic g-rays emitted by the residual nuclei. The cross sections for the two-particle emission channels (nn, np, na, aa) are much larger in the two heavy-ion reactions, 9e+9Be and 7Li + 11B, than in the a + 14C reaction. It is suggested that the large enhancement in the nn and np channels, which do not include any transfer processes, indicates that 9Be+ 9Be and 7Li + 11B form a largely deformed molecular state, from which only low-energy particles can be emitted. A broad resonance is observed at ∼ 28 MeV 18O excitation energy in the 9Be+9Be→ nn16O 7.12 MeV, 7 Li + 11 B → nn 16 O 7.12 MeV and 9 Be + 9 Be → np 16 N 0.397 MeV reaction channels.

Structural and optical characterization of implanted and annealed semi-insulating GaAs

Abstract The structural and optical properties of SI GaAs crystals implanted with Se, Si and Be ions have been studied. The implanted fluences ranged from 1012 to 1015 cm−2 at energies of 2.3 MeV (Be), 7 MeV (Si) and 10.9 MeV (Se), producing buried damaged layers centered at a depth of about 3 μm. Changes in the lattice constant were measured by XRD and the corresponding strain and damage profiles were determined and correlated with estimates of damage obtained from the results of channeling-RBS measurements. Both photoluminescence and Raman measurements were used to probe the damage as a function of depth with the aid of a shallow level produced by chemical etching. All measurements indicate a maximum of damage around 3 μm. Except for a region at the end of range, the crystal structure of p+ Be-doped GaAs has recovered its original quality upon annealing.