Ion channeling for strain analysis in buried nanofilms (

The title should have been: \"Ion channeling for strain anal. in buried nanofilms

Influence of steering effects on strain detection in AlGaInN/GaN heterostructures by ion channellin

Ion steering effects in the interface of heterostructures can strongly influence the shape and position of angular channelling scans leading to considerable error in the determination of strain by ion channelling. As an example, this paper presents channelling measurements on a near-lattice-matched AlGaInN/GaN heterostructure which show no shift between the angular scans from the quaternary layer and the underlying GaN substrate although high resolution x-ray diffraction data confirm the presence of strain in the layer. Such ‘anomalous’ behaviour was studied by means of Monte Carlo simulations for nitride ternary and quaternary films in the whole composition range. The simulations show that the thickness, magnitude of the distortion of the strained lattice and energy of the probing beam are critical parameters controlling the impact of steering. Three composition/strain regions were established for a typical beam of 2MeV alpha particles corresponding to different intensities of the steering potential and in which strain measurements by ion channelling are (a) correct, (b) possible but require corrections and (c) not possible due to steering effects

The 20Ne(α, γ)24Mg reaction

The reaction 20Ne(α, γ) 24Mg has been investigated in the energy range Eα = 1.2 to 3.2 MeV. Twelve resonances were observed. Gamma-ray angular distribution and correlation measurements yield a unique spin and parity assignment for ten 24Mg levels with excitation energies in the region Ex = 10.6−12.0 MeV. The resonance strengths and deduced radiative widths are reported. A strong preference is found for deexcitation through E2 radiation; E1 and M1 transitions are relatively weak, as expected from isospin selection rules

Levels of 32S excited in the 28Si (α, γ) 32S and 31P(p, γ) 32S reactions

Alpha-particle emitting levels of 32S, in the E, = 9- 10 MeV region, were studied by means of (α, γ) and (p, y) reactions. In the 28Si(α, γ)32S reaction, with α particles in the 2.0-3.3 MeV range, four resonances were observed, at E, = 2.618, 2.878, 2.904 and 3.162 MeV. The latter three correspond to 31P(p, y)32S resonances at E, = = 618.9, 642.1 and 875.5 keV. The spins and parities of the four resonant states, as determined by angular distribution and correlation measurements, are l-, 2+, l- and 2+, respectively. The (α, y) and (p, y) yields were also measured. From corresponding (α, y) and (p, y) resonance energies a Q value of 1919 & 4 keV is found for the 31P(p α)28Si reaction

Investigation of the 24Mg(α, γ)28Si reaction and some 27Al(p, γ)28Si resonances

The yield of 8–13 MeV γ radiation from the 24Mg(α, γ)28Si reaction has been measured in the Eα = 1.2–3.2 MeV range, making use of natural Mg and enriched 24Mg targets. Twenty resonances were observed, corresponding to 28Si levels in the Eχ = 11.3–12.8 MeV region. Six resonances show a relatively strong ground-state transition (γ0); the spin and parity (either 1-, or 2+) of these resonances was uniquely determined through angular distribution measurements. At nine other resonances the angular distribution was measured of γ1, the transition to the 28Si first excited state at 1.77 MeV; supplemented with angular correlation measurements in several different geometries, this uniquely determined the Jπ of these resonances. The remaining five resonances are weak. The strongest resonances have Jπ=2+ or 4+. These are deexcited through E2 or strongly mixed M1-E2 transitions. In both the 24Mg(α, γ)28Si and 27Al(p, γ)28Si reactions a level in 28Si at Eχ=12.24 MeV is excited. The (unique) spin determinations from these reactions, however, do not agree, yielding Jπ = 4+ and Jπ = 3+, respectively. Although the γ-ray single spectra are closely analogous, pronounced differences exist in the γ-γ coincidence spectra measured from the two reactions, showing that actually two closely spaced (ΔEχ ≈ 0.6 keV) levels in 28Si are excited. A new, extremely weak, resonance in the 27Al(p, γ)28Si reaction has been observed at Ep = 202.3 ± 0.9 keV. The data obtained from the 24Mg(α, γ)28Si reaction are compared with the information from the 27Al(p, γ)28Si and 27Al(p, α)24Mg reactions. From the measured yields of these three reactions, the partial widths Γα, Γp and Γγ are computed for most resonance levels

The Utrecht 850 kV cascade generator II. The beam integrator and galvanometer

A current integrator is described for the integration of currents from 0.01 to 500 μA with an accuracy of 0.1%. The principle used is essentially the same as that of the excellent circuit described earlier by Helmer and Hemmendinger. The modifications effected result in a considerable reduction in expense, as well as a lower input impedance. Due to increased high frequency gain much smaller condensers are necessary in order to maintain the input voltage within some hundredths of a volt of ground, at all times. The integrated current is measured as the number of output pulses, each pulse representing a fixed amount of change. Except for the condensers, no special components are used. A low-impedance electronic galvanometer for operation in series with this integra or is also described. This circuit combines the advantages of imperceptible zero drift, fixed calibration, and essentially absolute protection against burn-ou

Energy measurements of proton resonances in light nuclei

A search has been made for (p, γ) resonances in all stable nuclides from 19F through 33S for proton energies in the 0.20 – 0.85 MeV range. The energies of eighty-one resonances were measured with an average precision of 0.24 percent. Four new resonances, at 431.0 ± l.3, 436.9 ± 1.3, 480.1 ± l.0, and 725.5 ± 1.2 keV, were observed in the 22Ne(p, γ)23Na reaction, and one new resonance, at 501.4 ± l.4 keV, was found in the 25Mg(p, γ)26Al reaction