D. Kollewe

Scintillation properties of cerium-doped gadolinium-scandium-aluminum garnets

Abstract Optical properties and scintillation responses of cerium doped gadolinium-scandium-aluminum garnets (GSAG), pulled by the Czochralski method, were studied with regard to applications in scintillation counters. Scintillation responses were investigated for irradiation with charged particles, γ-rays and neutrons. The observed decay constant ( τ = 120 ns) is shorter than in common inorganic scintillators like NaI(T1) and bismuth germanate (BGO). The attenuation coefficient exceeds the value reported for Nal(T1). GSAG(Ce) shows a higher light yield (30% when compared with NaI(T1)) and better energy resolution (12.5% for 662 keV γ-rays from 137 Cs) than BGO. To demonstrate the feasibility for neutron detection, crystals were irradiated with slow neutrons (from 14.7 meV to 120 meV) from a neutron diffraction spectrometer at the Grenoble pile Melusine and fast neutrons (≥ 7.9 MeV) from the Stuttgart Dynamitron accelerator using the 9 Be(α, n) 12 C reaction.

Lattice site investigations for Mg in LiNbO3 by combined RBS-PIXE-NRA channeling experiments

The lattice position of magnesium in lithium niobate has been investigated for single crystals doped with MgO (between 0 and 9 mol% in the congruent melt) using a combination of RBS, PIXE and NRA with channeling. Mg seems to be collinear with the niobium and lithium in the c-axis for the whole concentration range. Concentration dependent effects with a threshold of about 1 mol% MgO for other axes have been observed. For low concentrations experimental results and computer simulations performed with our recently developed program CASSIS indicate that magnesium occupies an octahedral site near lithium while for higher concentrations the regular lithium site and an octahedral position near niobium is found to be occupied.

Surface refractive indices and profile widths of He implanted LiNbO3 waveguides

Abstract He implanted LiNbO 3 waveguides have been investigated by dark and bright line spectroscopy. The refractive index profiles were reconstructed with an improved inverse WKB procedure. In the region of electronic damage the resulting profiles are very reliable. Likewise the surface-side flank of nuclear damage induced refractive index decrease is reproduced with high accuracy. In contrast with other reconstruction schemes we determine refractive indices close to the surface with an accuracy better than 2 × 10 −4 . However, the full range of nuclear damage cannot be explored. We discuss how the profile parameters depend on ion energy and irradiation dose. At 3.17 MeV the helium enriched layer seems to saturate for doses above 5 × 10 15 cm −2 . Electronic damage increases the ordinary and decreases the extraordinary refractive index, more for higher doses and less for higher energies.

Performance of 10 × 10 mm2 pin silicon photocells used as high resolution charged particle detectors

Abstract By utilizing pin silicon photocells for energy spectrometry system resolutions of 11.92 keV for 5486 keV241 Am α-particles and 4.9 keV for 148.1 keV 212Bi conversion electrons have been achieved.

Channeling in Mg and Zr doped gadolinium gallium garnets

Abstract Single crystals of pure gadolinium gallium garnets (GGG) and magnesium and zircon doped GGG (GGMZ) have been investigated using particle channeling techniques. Angular dependences of the yield of particles or radiation close to the [100], [110] and [111] axes of thick single crystals were measured by means of Rutherford backscattering and particle induced X-ray emission (PIXE). Despite the complex lattice structure of garnets the experimental values of ψ 1 2 are in accord with the general channeling theory. Also the lattice sites of magnesium and zirconium could be determined.

Lattice site location of iron in potassium niobate

The lattice site of iron in potassium niobate has been investigated by channeling of He-ions in combination with simultaneous Rutherford backscattering analysis (RBS), nuclear reaction analysis (NRA) and particle induced X-ray emission (PIXE). He-ions with energies of 3.1 MeV were used at the Dynamitron accelerator of the university at Stuttgart. Oxygen was detected by the resonant 16O(α,α)16O nuclear reaction at 3.05 MeV. Two crystals containing 0.12 mol% iron cut perpendicular to the 〈100〉 and 〈110〉 axis directions according to the cubic configuration of the lattice have been examined. Angular PIXE yield profiles of axial channeling close to the 〈100〉, 〈110〉, 〈111〉 and 〈221〉 axes have been compared for iron, niobium and potassium. Also computer simulations have been performed and compared with the measured data. Close resemblance between the angular yield profiles for K and Fe has been found. Therefore we conclude that Fe occupies K lattice sites in Fe:KNbO3. This result is also supported by computer simulations.

Dependence of the 7Li(p, α)4He minimum yield on the Mg-concentration for proton channeling in LiNbO3:Mg

Abstract The dependence of the 7 Li(p, α) 4 He minimum yield on the magnesium concentration has been investigated for lithium niobate single crystals doped with MgO (between 0 and 9 mol% in the congruent melt) using proton channeling in combination with NRA. For all experimentally investigated axes — except the 〈0001〉-axis — systematic Mg-concentration dependent variations of the Li-NRA minimum yield have been observed. The comparison of these experimental observations with the results of the evaluations based on the continuum potentials supports the assignments for the lattice sites of Mg from recent IBA-experiments.

Comparison of strain and damage profiles induced by implantation of Xe+, Ne+ and H2+ ions in yttrium iron garnet

Abstract Ions of 120 keV Xe + , 100 keV Ne + and 120 keV H + 2 have been implanted to various doses in 2.6 μm epitaxial layers of yttrium iron garnet (Y 3 Fe 5 O 4 ) grown on 〈111〉 single crystal gadolinium gallium garnet. Rutherford backscattering and resonant 16 O(α, α) 16 O scattering of channeled 3.07 MeV 4 He + ions have been measured to study crystal distortions induced during room temperature implantation. Strain close to the surface was obtained from the angle change between 〈110〉 and 〈100〉 axes as measured by channeling in implanted and unimplanted parts of the crystal. The damage profile was obtained directly from the energy spectrum of backscattered particles. A simple method to evaluate strain profiles from the measured RBS (Rutherford Backscattering) spectra has been used.

Study of Bi-substituted iron garnet epilayers by means of channeling

Abstract Magnetic films of bismuth substituted iron garnets have been investigated using He ion channeling. Rutherford backscattering and ion induced X-ray emission measurements have been made as a function of the thickness of the garnet epilayers. The lattice sites of bismuth and lead could be determined.

Investigation of radiation damage in garnets produced by implantation of rare earth ions and its annealing

Abstract Synthetic garnet crystals (gadolinium gallium garnet GGG, yttrium aluminum garnet YAG) have been used to study the behaviour of the crystal lattice after implantation of heavy ions (cerium, praseodymium) with high energy (1.0 to 2.5 MeV) and varying doses. The radiation damage was analyzed using Rutherford backscattering spectrometry (RBS) combined with the channeling effect. Depth profiles of the defects, the amorphization dose and the penetration depth of the damage could be obtained and compared with simulation calculations. In some cases the depth profiles of the implanted ions themselves could be measured. With heat treatment at temperatures up to 1400°C the produced damage can be annealed almost completely.