Despite its widespread occurrence in nature and its importance in a variety of industrial applications, the nucleation and subsequent crystallization of calcium carbonate is still a matter of debate. Classical theory predicts that supersaturated carbonate solutions consist mostly of ions and ion pairs, with a small number of larger clusters present in the solution. However, for calcium carbonate solutions, this classical view has been challenged by the emergence of non-classical theories. In a novel experiment, using synchroton X-ray absorption spectroscopy, the molecular structure around the solvated calcium ion in dilute supersaturated calcium carbonate solutions was probed in situ.

Ultrasoft colloids typically do not spontaneously crystallize, but rather vitrify, at high concentrations. Combining in situ rheo–small-angle-neutron-scattering experiments and numerical simulations we show that shear facilitates crystallization of colloidal star polymers in the vicinity of their glass transition. With increasing shear rate well beyond rheological yielding, a transition is found from an initial bcc-dominated structure to an fcc-dominated one. This crystal-to-crystal transition is not accompanied by intermediate melting but occurs via a sudden reorganization of the crystal structure. Our results provide a new avenue to tailor colloidal crystallization and the crystal-to-crystal transition at the molecular level by coupling softness and shear.

High carrier density quantum wells embedded within a Mott insulating matrix present a rich arena for exploring unconventional electronic phase behavior ranging from non-Fermi-liquid transport and signatures of quantum criticality to pseudogap formation. Probing the proposed connection between unconventional magnetotransport and incipient electronic order within these quantum wells has however remained an enduring challenge due to the ultra-thin layer thicknesses required. Here we address this challenge by exploring ...

Ptychographic tomography can provide high-resolution quantitative 3D images of a sample. OMNY is an in-vacuum endstation that allows cryogenic sample conditions and a cryo load-lock system permits sample transfer of cryogenically fixed specimens. Accurate sample position required for the method is achieved via closed loop position control to a metrology system based on laser interferometry. OMNY is now in regular operation at the cSAXS beamline and proposals may be submitted. Typically, it is used for biological and other radiation sensitive samples such as polymers. First imaging results on biological samples can be found here.
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On February 20, 2018 the latest proposal submission deadline for the SINQ facility has passed. In total, 213 new beam time requests were submitted. In particular, the instruments for materials science and neutron imaging are strongly demanded: 93 proposals were received for those instruments followed by the instruments for small angle scattering and reflectometry (47 proposals). The review committees will gather on April 19-20 at PSI to evaluate the new proposals such that the users can be informed by the end of April. Due to the SINQ upgrade in 2019 this was the only proposal deadline in 2018. The date for the first call after the upgrade will be announced in due time.

At the end of the beam period in 2017, a new detector system has been installed and tested for the GPD instrument. It is composed out of small and independent units of scintillator blocks which are directly read out by silicon photomultipliers (SiPM). This therefore compact and modular system allows for an easy and quick change of detector geometry which is e.g. needed between transverse and longitudinal field measurements. Compared to the detector system used before, it features an increased solid angle coverage and time resolution as well as a smaller positron background. For the upcoming beam cycle, GPD will be equipped with additional passive entrance collimators which according to GEANT4 simulations will further reduce the background.

The annual Open Users’ Meeting (BVR: Benutzerversammlung Rinzyklotron) of the particle physics at the ring cyclotron took place February 12 -14, 2018 at PSI. As usual, the first day was devoted to detailed half-day review meetings of subcommittees with the international MEG, Mu3e, MUSE and nEDM collaborations. The committee-internal work framed the open meeting with progress reports and requests for beam time in the afternoon of Feb 13.
Following a well-received tradition, the open meeting started with a talk on theoretical developments, this time given by Professor Gilberto Colangelo from Bern and covering progress in the calculation of the anomalous g-factor of the muon - a very hot topic in precision particle physics.
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Contact: PSI User Office, Phone: +41-56-310-4666, Email: useroffice@psi.ch