Commissioning and operation of the Cherenkov detector for proton Flux Measurement of the UA9 Experiment

The UA9 Experiment at CERN-SPS investigates channeling processes in bent silicon crystals with the aim to manipulate hadron beams. Monitoring and characterization of channeled beams in the high energy accelerators environment ideally requires in-vacuum and radiation hard detectors. For this purpose the Cherenkov detector for proton Flux Measurement (CpFM) was designed and developed. It is based on thin fused silica bars in the beam pipe vacuum which intercept charged particles and generate Cherenkov light. The first version of the CpFM is installed since 2015 in the crystal-assisted collimation setup of the UA9 experiment. In this paper the procedures to make the detector operational and fully integrated in the UA9 setup are described. The most important standard operations of the detector are presented. They have been used to commission and characterize the detector, providing moreover the measurement of the integrated channeled beam profile and several functionality tests as the determination of the crystal bending angle. The calibration has been performed with Lead (Pb) and Xenon (Xe) beams and the results are applied to the flux measurement discussed here in detail.Comment: 25 pages, 14 figure

Temperature and Bias Voltage Dependence of the MPPC Detectors

to appear in the IEEE Transactions on Nuclear ScienceInternational audienceThis work reports on the characterization of the Multi-Pixel Photon Counter (MPPC) detectors as a function of the temperature and bias voltage. Devices of 1x1 mm2 and 3x3 mm2 total area and 50x50 µm2 µcell size produced by Hamamatsu Photonics have been studied. The temperature has been varied from -110°C to -50°C using a cryostat cooled by liquid nitrogen and from 0 to 38°C using a climatic chamber. Important electrical parameters of the MPPC detectors as gain, breakdown voltage, quenching resistance, capacitance and dark count rate have been measuredsubstrate (on the rear side) and by a metal layer (on the front side). Each µcell is represented by a p+/n junction working in Geiger-mode connected in series with its integrated passive quenching resistance. The detectors are operated with each µcell biased to a bias voltage Vbias above the breakdown voltage VBD. The Vbias exceeds the VBD by an amount called overvoltage ΔV = Vbias – VBD, which has a critical influence on detector performance

Thermodynamic properties and structural stability of thorium dioxide

Using density functional theory (DFT) calculations, we have systematically investigated the thermodynamic properties and structural stabilities of thorium dioxide (ThO$_2$). Based on the calculated phonon dispersion curves, we calculate the thermal expansion coefficient, bulk modulus, and heat capacities at different temperatures for ThO$_2$ under the quasi-harmonic approximation. All the results are in good agreement with corresponding experiments proving the validity of our methods. Our theoretical studies can help people more clearly understand the thermodynamic behaviors of ThO$_2$ at different temperatures. In addition, we have also studied possible defect formations and diffusion behaviors of helium in ThO$_2$, to discuss its structural stability. It is found that in intrinsic ThO$_2$ without any Fermi energy shifts, the interstitial Th$_i^{4+}$ defect other than oxygen or thorium vacancies, interstitial oxygen, and any kinds of Frenkel pairs, is most probable to form with an energy release of 1.74 eV. However, after upshifting the Fermi energy, the formation of the other defects also becomes possible. For helium diffusion, we find that only through the thorium vacancy can it happen with the small energy barrier of 0.52 eV. Otherwise, helium atoms can hardly incorporate or diffuse in ThO$_2$. Our results indicate that people should prevent upshifts of the Fermi energy of ThO$_2$ to avoid the formation of thorium vacancies and so as to prevent helium caused damages.Comment: 11 pages, 11 figure

Coral larvae for restoration and research: a large-scale method for rearing Acropora millepora larvae, inducing settlement, and establishing symbiosis

Here we describe an efficient and effective technique for rearing sexually-derived coral propagules from spawning through larval settlement and symbiont uptake with minimal impact on natural coral populations. We sought to maximize larval survival while minimizing expense and daily husbandry maintenance by experimentally determining optimized conditions and protocols for gamete fertilization, larval cultivation, induction of larval settlement by crustose coralline algae, and inoculation of newly settled juveniles with their dinoflagellate symbiont Symbiodinium. Larval rearing densities at or below 0.2 larvae mL -1 were found to maximize larval survival and settlement success in culture tanks while minimizing maintenance effort. Induction of larval settlement via the addition of a ground mixture of diverse crustose coralline algae (CCA) is recommended, given the challenging nature of in situ CCA identification and our finding that non settlement-inducing CCA assemblages do not inhibit larval settlement if suitable assemblages are present. Although order of magnitude differences in infectivity were found between common Great Barrier Reef Symbiodinium clades C and D, no significant differences in Symbiodinium uptake were observed between laboratory-cultured and wild-harvested symbionts in each case. The technique presented here for Acropora millepora can be adapted for research and restoration efforts in a wide range of broadcast spawning coral species

Coral larvae for restoration and research: a large-scale method for rearing Acropora millepora larvae, inducing settlement, and establishing symbiosis

Here we describe an efficient and effective technique for rearing sexually-derived coral propagules from spawning through larval settlement and symbiont uptake with minimal impact on natural coral populations. We sought to maximize larval survival while minimizing expense and daily husbandry maintenance by experimentally determining optimized conditions and protocols for gamete fertilization, larval cultivation, induction of larval settlement by crustose coralline algae, and inoculation of newly settled juveniles with their dinoflagellate symbiont Symbiodinium. Larval rearing densities at or below 0.2 larvae mL -1 were found to maximize larval survival and settlement success in culture tanks while minimizing maintenance effort. Induction of larval settlement via the addition of a ground mixture of diverse crustose coralline algae (CCA) is recommended, given the challenging nature of in situ CCA identification and our finding that non settlement-inducing CCA assemblages do not inhibit larval settlement if suitable assemblages are present. Although order of magnitude differences in infectivity were found between common Great Barrier Reef Symbiodinium clades C and D, no significant differences in Symbiodinium uptake were observed between laboratory-cultured and wild-harvested symbionts in each case. The technique presented here for Acropora millepora can be adapted for research and restoration efforts in a wide range of broadcast spawning coral species

Coral larvae for restoration and research: A large-scale method for rearing Acropora millepora larvae, inducing settlement, and establishing symbiosis

© 2017 Pollock et al. Here we describe an efficient and effective technique for rearing sexually-derived coral propagules from spawning through larval settlement and symbiont uptake with minimal impact on natural coral populations. We sought to maximize larval survival while minimizing expense and daily husbandry maintenance by experimentally determining optimized conditions and protocols for gamete fertilization, larval cultivation, induction of larval settlement by crustose coralline algae, and inoculation of newly settled juveniles with their dinoflagellate symbiont Symbiodinium. Larval rearing densities at or below 0.2 larvae mL-1 were found to maximize larval survival and settlement success in culture tanks while minimizing maintenance effort. Induction of larval settlement via the addition of a ground mixture of diverse crustose coralline algae (CCA) is recommended, given the challenging nature of in situ CCA identification and our finding that non settlement-inducing CCA assemblages do not inhibit larval settlement if suitable assemblages are present. Although order of magnitude differences in infectivity were found between common Great Barrier Reef Symbiodinium clades C and D, no significant differences in Symbiodinium uptake were observed between laboratory-cultured and wild-harvested symbionts in each case. The technique presented here for Acropora millepora can be adapted for research and restoration efforts in a wide range of broadcast spawning coral species

Characteristics of a prototype matrix of Silicon PhotoMultipliers (SiPM)

International audienceThis work reports on the electrical (static and dynamic) as well as on the optical characteristics of a prototype matrix of Silicon Photomultipliers (SiPM). The prototype matrix consists of 4 × 4 SiPM's on the same substrat fabricated at FBK-irst (Trento, Italy). Each SiPM of the matrix has an area of 1 × 1mm2 and it is composed of 625 microcells connected in parallel. Each microcell of the SiPM is a GM-APD (n+/p junction on P+ substrate) with an area of 40 × 40 μm2 connected in series with its integrated polysilicon quenching resistance. The static characteristics as breakdown voltage, quenching resistance, post-breakdown dark current as well as the dynamic characteristics as gain and dark count rate have been analysed. The photon detection efficiency as a function of wavelength and operation voltage has been also estimated

Self-recognition in corals facilitates deep-sea habitat engineering

The ability of coral reefs to engineer complex three-dimensional habitats is central to their success and the rich biodiversity they support. In tropical reefs, encrusting coralline algae bind together substrates and dead coral framework to make continuous reef structures, but beyond the photic zone, the cold-water coral Lophelia pertusa also forms large biogenic reefs, facilitated by skeletal fusion. Skeletal fusion in tropical corals can occur in closely related or juvenile individuals as a result of non-aggressive skeletal overgrowth or allogeneic tissue fusion, but contact reactions in many species result in mortality if there is no ‘self-recognition’ on a broad species level. This study reveals areas of ‘flawless’ skeletal fusion in Lophelia pertusa, potentially facilitated by allogeneic tissue fusion, are identified as having small aragonitic crystals or low levels of crystal organisation, and strong molecular bonding. Regardless of the mechanism, the recognition of ‘self’ between adjacent L. pertusa colonies leads to no observable mortality, facilitates ecosystem engineering and reduces aggression-related energetic expenditure in an environment where energy conservation is crucial. The potential for self-recognition at a species level, and subsequent skeletal fusion in framework-forming cold-water corals is an important first step in understanding their significance as ecological engineers in deep-seas worldwide