The new versatile general purpose surface-muon instrument (GPS) based on silicon photomultipliers for μ{\mu}SR measurements on a continuous-wave beam

We report on the design and commissioning of a new spectrometer for muon-spin relaxation/rotation studies installed at the Swiss Muon Source (S$\mu$S) of the Paul Scherrer Institute (PSI, Switzerland). This new instrument is essentially a new design and replaces the old general-purpose surface-muon instrument (GPS) which has been for long the workhorse of the $\mu$SR user facility at PSI. By making use of muon and positron detectors made of plastic scintillators read out by silicon photomultipliers (SiPMs), a time resolution of the complete instrument of about 160 ps (standard deviation) could be achieved. In addition, the absence of light guides, which are needed in traditionally built $\mu$SR instrument to deliver the scintillation light to photomultiplier tubes located outside magnetic fields applied, allowed us to design a compact instrument with a detector set covering an increased solid angle compared to the old GPS.Comment: 11 pages, 11 figure

Relatório dos projetos concluídos 2009.

bitstream/item/58245/1/doc138.pd

Relatório dos projetos concluídos 2011.

bitstream/item/79693/1/Doc-156.pdfProjeto/Plano de Ação: 11.11.11.111

A time-resolution study with a plastic scintillator read out by a Geiger-mode Avalanche Photodiode

In this work we attempt to establish the best time resolution attainable with a scintillation counter consisting of a plastic scintillator read out by a Geiger-mode Avalanche Photodiode. The measured time resolution is inversely proportional to the square root of the energy deposited in the scintillator, and scales to 18ps (sigma) at 1MeV. This result competes with the best ones reported for photomultiplier tubes.Comment: 8 pages, 8 figure

Behaviour of a muonic atom as an acceptor centre in diamond

Polarized negative muons were used to study the behaviour of the boron acceptor centre in synthetic diamond produced by the chemical vapour deposition (CVD) method. The negative muon substitutes one of the electrons in a carbon atom, and this muonic atom imitates the boron acceptor impurity in diamond. The temperature dependence of the muon spin relaxation rate and spin precession frequency were measured in the range of 20 - 330 K in a transverse magnetic field of 14 kOe. For the first time a negative shift of the muon spin precession was observed in diamond. It is tentatively attributed to an anisotropic hyperfine interaction in the boron acceptor. The magnetic measurements showed that the magnetic susceptibility of the CVD sample was close to that of the purest natural diamond.Comment: 8 pages, 3 figure

Relatório dos projetos concluídos 2010.

bitstream/item/46830/1/Documento-144.pdfProjeto: 11.11.11.111

Closed-loop recycling of plastics enabled by dynamic covalent diketoenamine bonds.

Recycled plastics are low-value commodities due to residual impurities and the degradation of polymer properties with each cycle of re-use. Plastics that undergo reversible polymerization allow high-value monomers to be recovered and re-manufactured into pristine materials, which should incentivize recycling in closed-loop life cycles. However, monomer recovery is often costly, incompatible with complex mixtures and energy-intensive. Here, we show that next-generation plastics-polymerized using dynamic covalent diketoenamine bonds-allow the recovery of monomers from common additives, even in mixed waste streams. Poly(diketoenamine)s 'click' together from a wide variety of triketones and aromatic or aliphatic amines, yielding only water as a by-product. Recovered monomers can be re-manufactured into the same polymer formulation, without loss of performance, as well as other polymer formulations with differentiated properties. The ease with which poly(diketoenamine)s can be manufactured, used, recycled and re-used-without losing value-points to new directions in designing sustainable polymers with minimal environmental impact

Internal erosion of granular materials – Identification of erodible fine particles as a basis for numerical calculations

In geohydromechanics internal erosion is a process which is still hardly to be quantified both spatially as well as temporally. The transport of fine particles, which is caused by increased hydraulic gradients, is influenced by the pore structure of the coarse grained fabric. The microstructural information of the pore constriction size distribution (CSD) of the solid skeleton has therefore to be taken into account when internal erosion is analyzed either analytically or numerically. The CSD geometrically defines the amount of fine particles, which potentially can be eroded away for a given hydraulic force. The contribution introduces experimental and numerical calculations which aim at the quantification of the amount of erodible fines. Based on this approach a multiphase continuum-based numerical model is used to back calculate the process of internal erosion for one material of the well-known experimental investigation of Skempton & Brogan (1994)[1]

A lens-coupled scintillation counter in cryogenic environment

In this work we present an elegant solution for a scintillation counter to be integrated into a cryogenic system. Its distinguishing feature is the absence of a continuous light guide coupling the scintillation and the photodetector parts, operating at cryogenic and room temperatures respectively. The prototype detector consists of a plastic scintillator with glued-in wavelength-shifting fiber located inside a cryostat, a Geiger-mode Avalanche Photodiode (G-APD) outside the cryostat, and a lens system guiding the scintillation light re-emitted by the fiber to the G-APD through optical windows in the cryostat shields. With a 0.8mm diameter multiclad fiber and a 1mm active area G-APD the coupling efficiency of the "lens light guide" is about 50%. A reliable performance of the detector down to 3K is demonstrated.Comment: 14 pages, 11 figure