compton photon calorimeter gregg franklin, b. quinn carnegie mellon
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
Compton Photon CalorimeterGregg Franklin, B. QuinnCarnegie Mellon
Design Considerations• Light Yield and Photoelectrons• Detector Geometry, EGS Simulations, Linearity• Decay time• Crystal Properties
,
,
energy of bin i
mean photoelectrons per photon of energy
=mean number of photons of energy
pe i i iphotonenergybin
i
i i
i i
n N E
where
E
E
N E
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
22i ii
22i ii
-( ) / 2-(N ) / 2pe i
-( / ) /(2 / N )-(N ) / 2
Prob(n , E ) e e
e e (using N )
i pe ii
pe i i ii
E n EN
n E ENi
2 2 2,
1= (1+ ) n i i i ii
E N E
max 2
0,
max
0
11
E
n sumEsum
Esum pe
dNdE E
dE EdNE n dE EdE
Probability of getting npe photoelectrons from Compton Photons of energy Ei
photonsphotonsgiving npe photoelectrons
Convolution of two gaussians gives variance for npe,i:
If energy independent, error on summed energy is: Finite photoelectronterm small ifEmax large
Measured Energy Deposited (MeV)
20 MeV
5 MeV
1MeV
Measured energy deposited for1 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 onlyphotoelectron statistics andPMT gain variance
• Detector Geometry, EGS Simulations, Linearity
EGS simulation by Brian Quinn
12.75 MeV photons
ISaint-Gobain“BrilLanCe 380”LaBr3(Cd)
Density: 5.29 g/cm3
1 inch diam.4 inch thick(~ 5.3 rad lengths)
Energy Deposited
511 keVescape 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 inanalyzing power
1 MeV
Analyzing Power of summed Deposited Energy as function of Deposited Energy Threshold
% change in Analyzing Power
1.5%
3.0%
EDep Thresh.
EDep 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 BGO GSO CeF3BriLanCe
380PreLude
420
Density
(6/cm3)8.30 7.13 6.70 6.16 5.29 7.1
Rad Length
(cm)0.90 1.12 1.39 1.68 ~1.9 1.2
Moliere Radius
(cm)2.0 2.3 2.4 2.6 ? ?
Decay time
(ns)50 300 56:600 30 16 41
Light output
(% NaI)0.4% 9% 45% 6.6% 165% 84%
photoelectrons
(# / MeV)8 170 850 125 3150 1600
$$$
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