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Compton Photon Calorimeter Gregg Franklin, B. Quinn Carnegie Mellon

Compton Photon Calorimeter Gregg Franklin, B. Quinn Carnegie Mellon. Design Considerations Light Yield and Photoelectrons Detector Geometry, EGS Simulations, Linearity Decay time Crystal Properties. Light yield and Photoelectrons.

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Compton Photon Calorimeter Gregg Franklin, B. Quinn Carnegie Mellon

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  1. Compton Photon Calorimeter Gregg Franklin, B. Quinn Carnegie Mellon • Design Considerations • Light Yield and Photoelectrons • Detector Geometry, EGS Simulations, Linearity • Decay time • Crystal Properties

  2. Light yield and Photoelectrons Calculate contribution of finite photoelectrons per MeV energy deposited First, write mean total photoelectrons as: (integrated flux) x (Compton cross section d/dE) x (bin size)

  3. Probability of getting npe photoelectrons from Compton Photons of energy Ei photons giving npe photoelectrons photons Convolution of two gaussians gives variance for npe,i: If  energy independent, error on summed energy is: Finite photoelectron term small if Emax large

  4. Photoelectrons not a big issue for integrated energy BUT: Electron tagged data may be easier to analyze with more photoelectrons +Other calibration issues? 1MeV 20 MeV 5 MeV Measured energy deposited for 1 Mev, 5 MeV, and 20 MeV energy deposions Simulation includes only photoelectron statistics and PMT gain variance Measured Energy Deposited (MeV)

  5. Detector Geometry, EGS Simulations, Linearity EGS simulation by Brian Quinn 12.75 MeV photons ISaint-Gobain “BrilLanCe 380” LaBr3(Cd) 1 inch diam. 4 inch thick (~ 5.3 rad lengths) 511 keV escape peaks Density: 5.29 g/cm3 Energy Deposited

  6. Infinite slab still looses energy due to backscattering Finite slab energy loss goes up with photon energy

  7. Linearity improves with thickness, but is it important? 4 inches

  8. 3.0% Analyzing Power of summed Deposited Energy as function of Deposited Energy Threshold 1.5% EDep Thresh. 25 MeV % change in Analyzing Power 1% change in analyzing power 1 MeV EDep Thresh. 5 MeV

  9. Decay Time Consideration • Why not use BGO (decay time ~300 nS)? • Bremstrahlung • If ~10 kHz and “deadtime” 3* 300 ns, get 1% deadtime • Other • Coincidence and singles data • Electronics set up for ~100 nS gate • Larger background from tails • Prefer faster decay time (50 ns?)

  10. Crystal Properties

  11. This summer • Need to settle on crystal (at least for test) • Test FADC algorithm at CMU this summer • Gated and integrating modes (simulate summing algorithm) • Does ADC sum represent #photoelectrons? • Test resolution on sources • Need to slow down signal? • Possibly clip large pulses? • Better linearity simulations • GEANT4 (Optimization by Guido, some work at CMU)

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