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By Chris Ketter 26 Sept. 2014

Analysis of Saint-Gobain Scintillating Optical Fibers for use as Wave Guides for Cerenkov-Ring-Imaging-MPPC Array. By Chris Ketter 26 Sept. 2014. Introduction.

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By Chris Ketter 26 Sept. 2014

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  1. Analysis of Saint-Gobain Scintillating Optical Fibers for use as Wave Guides for Cerenkov-Ring-Imaging-MPPC Array By Chris Ketter26 Sept. 2014

  2. Introduction • The Hamamatsu MPPCs make a good candidate for detecting single photons produced by Cerenkov radiation, while within a magnetic field. The drawback is a small detector area (1x1 mm) and large footprint (6x5 mm). • R. Dolenec et al. investigated the use of cone-shaped light guides underneath their Aerogel (n=1.03) radiator. They improved their LGP from 1.6 to 3.7 γ/ring, a 230% improvement. • This presentation investigates the possibility of using plastic fibers as light guides to “fan-out” Cerenkov-photons onto the MPPCs.

  3. Overview • What fibers are available from Saint-Gobain and what is their optical acceptance? • What kind of radiator will meet the needs? • θ_cerenkov < θ_max of fibers? • works with acrylic adhesive? • other adhesives? • Luminosity predictions?

  4. Plastic Scintillating Fibers • Two general types available with an assortment of sizes and shapes. • Cladding: • Single-Clad: • NA = 0.58, so θ_max = 35° • Multi-Clad: • NA = 0.74, so θ_max =48° • Shapes: • Round: (3.44%)/(5.6%) trapping efficiency for single-/multi-clad respectively. • Square: (4.4%)/(7.3%) respectively. • Others: • BCF-91A shifts blue to green with 12 ns decay time. • BCF-92 shifts blue to green with a 2.7 ns decay time. • BCF-98 is designed for waveguide applications.

  5. Fiber Construction • Core: • Polystyrene • n = 1.60 • Cladding: • Acrylic • n = 1.49 • 3% or 4% thickness (round or square, respectively) • Secondary Cladding: • Fluor-Acrylic • n = 1.42 • 1% or 2% thickness (round or square, respectively)

  6. Wavelength-Shifting Fibers Emission Spectra • MPPC peak sensitivity around 450~500 nm. • Cernerkov phontons peak in UV range, and fall like 1/λ^2 • Either of these would help shift Cerenkov photons toward the MPPC’s sensitive range. BCF-92 has it’s absorption peak nearer the UV region and is faster than its counterpart, BCF-91a. • Drawback: wavelength shifting fibers are not scintillators, so the center would have to be reconstructed from tracker data. Reference: Saint-Gobain datasheet

  7. Radiator • Given that the maximum acceptance of the fibers is 35° and 48° for single- and multi-clad fibers, we want our index to be sufficiently small. • The acceptance angle for our trackers will be ~A°, so we want to be able to accept muons skewed by up to ~A°. Theta should be less than 48° – A°. • If theta is too small, then we’ll need a thicker radiator and hence will loose resolution on the ring diameter.

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