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

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

Probability of getting n pe photoelectrons from Compton Photons of energy E i photons giving n pe photoelectrons Convolution of two gaussians gives variance for n pe,i : If energy independent, error on summed energy is: Finite photoelectron term small if E max large

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

Detector Geometry, EGS Simulations, Linearity EGS simulation by Brian Quinn MeV photons ISaint-Gobain BrilLanCe 380 LaBr 3 (Cd) Density: 5.29 g/cm 3 1 inch diam. 4 inch thick (~ 5.3 rad lengths) Energy Deposited 511 keV escape peaks

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

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

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

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?)

PbWO4 BGOGSOCeF 3 BriLanCe 380 PreLude 420 Density (6/cm 3 ) Rad Length (cm) ~ Moliere Radius (cm) ?? Decay time (ns) : Light output (% NaI) 0.4%9%45%6.6%165%84% photoelectrons (# / MeV) $$$ 4 in max Natural decay Crystal Properties

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) This summer