Scientific Highlights from PSI's research departments

NUM (Condensed Matter Research with Neutrons and Muons)

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SYN (Synchrotron Radiation and Nanotechnology)

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ENE (General Energy)

Flow modeling in gas diffusion layers of PEFCs at the micro- and mesoscale.

The optimization of thermochemical and electrochemical conversion systems is of high mportance for a sustainable energy future society. Of particular interest regarding the performance of polymer electrolyte fuel cells (PEFCs) is the study of the gas flow in the gas diffusion layers (GDL). More specifically, permeability and diffusivity measurements in a model PEFC under normal operating conditions are highly desirable. As laboratory-measurements of these quantities under such conditions are very demanding, an alternative is the use of computer-based simulations. For this, two key elements are needed: a) an advanced numerical tool capable of modeling key microscale processes, and b) in-situ X-ray tomographic microscopy (XTM) scans of the GDL material. Physical modeling of 3D gas flows is accomplished through novel mesoscale computational algorithms based on the lattice Boltzmann method (LBM).

The provided figure illustrates computed flow streamlines through the GDL porous structure (carbon fiber paper Toray TGPH 060, domain size: 444x222x160 microns). The GDL microstructures, wherein the produced liquid water can be distinguished from the solid material, are obtained at the TOMCAT beamline of the Swiss Light Source (SLS). The results show that permeability and relative effective diffusivities of dry and partially liquid saturated GDL samples follow a relation proportional to (1-s)x, where (s) is the saturation level and the exponent x is approximately 3.

Presentation slides

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BIO (Biology and Chemistry)

The low-energy β− and electron emitter 161Tb as an alternative to 177Lu for targeted radionuclide therapy

Research Department Biology and Chemistry (BIO), Radionuclicde Development Group, Head Konstantin Zhernosekov. The low-energy β− emitter 161Tb is very similar to 177Lu with respect to half-life, beta energy and chemical properties. However, 161Tb also emits a significant amount of conversion and Auger electrons. Greater therapeutic effect can therefore be expected in comparison to 177Lu. It also emits low-energy photons that are useful for gamma camera imaging. The 160Gd(n,γ)161Gd→161Tb production route was used to produce 161Tb by neutron irradiation of massive 160Gd targets (up to 40 mg) in nuclear reactors. A semiautomated procedure based on cation exchange chromatography was developed and applied to isolate no carrier added (n.c.a.) 161Tb from the bulk of the 160Gd target and from its stable decay product 161Dy. 161Tb was used for radiolabeling DOTA-Tyr3-octreotate; the radiolabeling profile was compared to the commercially available n.c.a. 177Lu. A 161Tb Derenzo phantom was imaged using a small-animal single-photon emission computed tomography camera. Up to 15 GBq of 161Tb was produced by long-term irradiation of Gd targets. Using a cation exchange resin, we obtained 80%–90% of the available 161Tb with high specific activity, radionuclide and chemical purity and in quantities sufficient for therapeutic applications. The 161Tb obtained was of the quality required to prepare 161Tb–DOTA-Tyr3-octreotate. We were able to produce 161Tb in n.c.a. form by irradiating highly enriched 160Gd targets; it can be obtained in the quantity and quality required for the preparation of 161Tb-labeled therapeutic agents.

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GFA (Department Large Research Facilities)

Minimum emittance coupling in the SLS

Recent measurements of the vertical beam size in the SLS have shown that the value of the vertical emittance is ~ 3.2 pm-rad, close to the fundamental limit set by the quantum nature of synchrotron radiation (~ 0.5 pm-rad). The vertical beam size was determined using an optical imaging device especially built for this purpose. In this device the images are formed from vertically polarised light emitted by the electron beam in the visible to UV part of the spectrum. The new monitor allows determination of vertical beam sizes below 10 microns with sub-micron accuracy. The emittance is determined from the measured beam size and prior knowledge of the betatron and dispersion functions at the source point, determined by other means. This extremely small vertical emittance testifies to the careful reduction of transverse emittance coupling (0.05%) obtained in the SLS by virtue of carefully adjusting the settings of the ring lattice. To the best of our knowledge, this is the lowest reported coupling in an electron storage ring.