Events at Physics |
Events on Thursday, May 5th, 2011
- R. G. Herb Condensed Matter Seminar
- Complex Materials, Calorimetry, and Energy Landscapes
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Alexandra Navrotsky, University of California - Davis
- Abstract: Freed from the "tyranny of equilibrium", modern synthetic solid state chemists are producing nanomaterials, metastable phases, cluster compounds, and mixed organic-inorganic materials in a wealth of structures with amazing properties. Calorimetric studies have shown that many of these polymorphs or closely related materials are in fact very similar in energy, tracing out "energy landscapes" as a function of density, crystallinity, hydration, or other parameters. This talk focuses on new experimental thermodynamic results in three classes of materials: (1) amorphous and crystalline carbonates in the CaCO3 - MgCO3 - H2O system, (2) zeolites, mesoporous silicas, and metal organic frameworks (MOF), and (3) polynuclear cluster compounds in aluminum and uranium based systems.
- Host: Pupa Gilbert
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- The Development of Large Area Microchannel Plate Photodetectors
- Time: 4:00 pm
- Place: 4274 Chamberlin Hall
- Speaker: Bob Wagner, Argonne
- Abstract: The Large Area Picosecond Photodetector Development Collaboration is comprised of groups from three national laboratories, five U.S. universities, and two small U.S. companies working on a three-year project to develop a new generation of economical, large area (400 cm2) microchannel plate photomultipliers that can be tailored for a wide variety of applications in particle physics, medical imaging, and high energy astrophysics. In parallel with the development of the detector, a readout technology based on a switched capacitor array waveform sampling chip with time resolution in the 10 picosecond range is being developed that would allow particle identification by time-of-flight in the multi-GeV energy range. The basic photomultiplier incorporates a bialkali photocathode and a glass capillary microchannel plate pair functionalized by atomic layer deposition (ALD) to produce photoelectrons from incident visible light photons and produce gains of greater 106. Borosilicate glass capillary plates with pore size of 20-40 microns provide an inexpensive substrate compared to the standard lead-glass used in commercial microchannel plates. ALD allows the resistive and secondary emissive functions of the plates to be fabricated separately and economically. The collaboration is characterizing a variety of candidate materials for the coatings in order to optimize the gain and stability of the microchannel plates. Plates with gain of 50,000-70,000 at 1000V. bias have been produced on 33mm diameter substrates. The first 20cm by 20cm square glass capillaries were recently delivered to the project. Two alternatives for assembly and hermetic sealing of the photodetector are being pursued in parallel: a traditional ceramic housing with a strip line anode structure with embedded pins for signal output and high voltage connection, and an all borosilicate glass housing with a silk-screened silver strip line anode readout. The latter represents a potentially very inexpensive method of tube fabrication. An external printed circuit board with a matching strip line layout provides a means of transmitting the signal to the waveform sampling chips while maintaining a 50 ohm impedance from strip line to front-end input. The talk will review the history and current status of the project, summarize potential applications of the photodetector, and outline plans for the future development and production of the photomultiplier.
- Host: Teresa Montaruli