Design and Construction of a Slow Positron Beam for Solid and Surface Investigations

Anwand, W.; Bräuer, G.; Butterling, Maik; Kissener, H.R.; Wagner, A.

doi:10.4028/www.scientific.net/ddf.331.25

Cited by 94 publications

(85 citation statements)

References 20 publications

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“…For structural characterization, µ-Raman spectroscopy has been performed by using a Nd:YAG Laser with 532 nm wavelength in the scattering geometry using a liquid nitrogen cooled charge-coupled device camera. Positron annihilation Doppler broadening spectroscopy (DBS) was applied to clarify the nature of defects using the mono-energetic slow position beam "SPONSOR" [47]. High-resolution transmission electron microscopy (HR-TEM) investigations were done with an image-corrected Titan 80-300 microscope (FEI) operated at an accelerating voltage of 300 keV.…”

Section: Methodsmentioning

confidence: 99%

Defect-induced magnetism in SiC: Interplay between ferromagnetism and paramagnetism

et al. 2015

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Defect-induced ferromagnetism has triggered a lot of investigations and controversies. The major issue is that the induced ferromagnetic signal is so weak that it can sufficiently be accounted for by trace contamination. To resolve this issue, we studied the variation of the magnetic properties of SiC after neutron irradiation with fluence covering four orders of magnitude. A large paramagnetic component has been induced and scales up with defect concentration, which can be well accounted for by uncoupled divacancies. However, the ferromagnetic contribution is still weak and only appears in the low fluence range of neutrons or after annealing treatments. First-principles calculations hint towards a mutually exclusive role of the concentration of defects: a higher defectconcentration favors a larger magnetic interaction at the expense of spin polarization. Combining both experimental and first-principles calculation results, the defect-induced ferromagnetism can probably be understood as a local effect which cannot be scaled up with the volume. * Electronic address: s.zhou@hzdr.de 2

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Section: Methodsmentioning

confidence: 99%

Defect-induced magnetism in SiC: Interplay between ferromagnetism and paramagnetism

et al. 2015

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“…As for the MePS source the beam repetition rate can be matched to the positron annihilation lifetime thus optimizing for high average intensity and low detector pile-up distortions. mono-energetic positron beam SPONSOR (Slow POsitroN System Of Rossendorf) [13]. Here, Doppler-broadening studies are performed with higher statistics and more energy steps.…”

Section: The Gamma-induced Positron Source Gipsmentioning

confidence: 99%

Positron annihilation lifetime spectroscopy at a superconducting electron accelerator

Wagner

Anwand

Attallah

et al. 2017

J. Phys.: Conf. Ser.

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Abstract. The Helmholtz-Zentrum Dresden-Rossendorf operates a superconducting linear accelerator for electrons with energies up to 35 MeV and average beam currents up to 1.6 mA. The electron beam is employed for production of several secondary beams including X-rays from bremsstrahlung production, neutrons, and positrons. The secondary positron beam after moderation feeds the Monoenergetic Positron Source (MePS) where positron annihilation lifetime (PALS) and positron annihilation Doppler-broadening experiments in materials science are performed in parallel. The adjustable repetition rate of the continuous-wave electron beams allows matching of the pulse separation to the positron lifetime in the sample under study. The energy of the positron beam can be set between 0.5 keV and 20 keV to perform depth resolved defect spectroscopy and porosity studies especially for thin films.

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“…Positron lifetimes were calculated for the non-irradiated W-Ti-ODS samples with the PALSfit program package [22,28] and are displayed for the different materials in Table 1. All samples clearly show two different life times in the range of τ1 ~115 … 124 ps and τ2 ~ 249 … 327 ps.…”

Section: Pas Resultsmentioning

confidence: 99%

“…In order to identify the nature of the defects created by He implantation, positron annihilation DBS measurements were carried out with the mono-energetic slow positron beam ''SPONSOR'' at HZDR [21,22] at which a variation of the positron energy E from 30 eV to 36 keV with a smallest step width of 50 eV, if required, is possible. The energy resolution of the Ge detector at 511 keV was (1.09 + 0.01) keV, resulting in a high sensitivity to changes in material properties from surface to a depth of several µm.…”

Section: Doppler Broadening Spectroscopymentioning

confidence: 99%

Evaluation of defect formation in helium irradiated Y2O3 doped W-Ti alloys by positron annihilation and nanoindentation

Richter

Anwand

Chen

et al. 2017

Journal of Nuclear Materials

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Helium implanted tungsten-titanium ODS alloys are investigated using positron annihilation spectroscopy and nanoindentation. Titanium reduces the brittleness of the tungsten alloy, which is manufactured by mechanical alloying. The addition of Y2O3 nanoparticles increases the mechanical properties at elevated temperature and enhances irradiation resistance. Helium ion implantation was applied to simulate irradiation effects on these materials. The irradiation was performed using a 500 kV He ion implanter at fluences around 5 x 10 15 cm -2 for a series of samples both at room temperature and at 600 °C. The microstructure and mechanical properties of the pristine and irradiated W-Ti-ODS alloy are compared with respect to the titanium and Y2O3 content. Radiation damage is studied by positron annihilation spectroscopy analyzing the lifetime and the Doppler broadening. Three types of helium-vacancy defects were detected after helium irradiation in the W-Ti-ODS alloy: small defects with high heliumto-vacancy ratio (low S parameter) for room temperature irradiation, larger open volume defects with low helium-to-vacancy ratio (high S parameter) at the surface and He-vacancy complexes pinned at nanoparticles deeper in the material for implantation at 600 °C. Defect induced hardness was studied by nanoindentation. A drastic hardness increase is observed after He ion irradiation both for room temperature and elevated irradiation temperature of 600 °C. The Ti alloyed tungsten-ODS is more affected by the hardness increase after irradiation compared to the pure W-ODS alloy.3

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Design and Construction of a Slow Positron Beam for Solid and Surface Investigations

Cited by 94 publications

References 20 publications

Defect-induced magnetism in SiC: Interplay between ferromagnetism and paramagnetism

Defect-induced magnetism in SiC: Interplay between ferromagnetism and paramagnetism

Positron annihilation lifetime spectroscopy at a superconducting electron accelerator

Evaluation of defect formation in helium irradiated Y2O3 doped W-Ti alloys by positron annihilation and nanoindentation

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