Characterization of a 12fold segmented MINIBALL detector

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• Characterization of a 12-fold segmented MINIBALL
  detector
• The confirmation of an anisotropic hole mobility
  model
• B. Bruyneel, P. Reiter, J. Eberth and D.
  Weisshaar - IKP, Universität zu Köln

Application ?-ray tracking ? Pulse shape
analysis ? Detector response simulation ? Detector
characterization
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• Position Sensitivity (Single interaction)
• ? 1 ? ?x 1mm
• ? 5 ? ?x 2mm
• ?2 ?2noise ?2simulation
• Characterization Simulation input
• Electrical field Space Charge 4p.
• Crosstalk Amplitudes 2x(13x13)p.
• Electronic Response functions 13f.
• Crystal orientation 1p.
• Electron mobility 6p.
• Hole mobility 6p.
• Relative trigger delays ?p.

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The Electric Field

• Space Charge 1010/cm3
• cylinder symmetrical
• Linear in z and r
• 4 point fit from mobility data

E-field tangential to passivated back
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Crosstalk Detection
Inducing signal
Derivative fraction Core to Seg unknown Front
Seg to back 700ns Back Seg to
front 500ns Other lt 300ns
Prop. Frac. OLD NEW Core to Back
Seg -0.66 -0.47 Core to Front
Seg -0.30 -0.22 Front to Back -0.77 -0.03 Ba
ck to Front -0.44 -0.08 Other lt 0.1 lt0.1
Induced signal
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Crosstalk Detection
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Crosstalk Detection
Fit of Seg12 with 0.72 Seg6 and 503ns dSeg6/dt
Event A-B All segments
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Response Functions

• Averaging using linear interpolation

Tav(t) build with 400Mhz sampling!!!
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Response Functions

• Averaging using linear interpolation

Tav(t) build with 400Mhz sampling!!!
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Electron and Hole Mobility in Ge
-Phys.Rev. 130(6)2201-2204,1963 -distributed
over 4 ellipsoidal valleys -each valley is MB
distributed, T(E) -intervalley scattering ?(E)
defines valley population -v100(E) and ?(E)
defines all.
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Hole mobility the anisotropic model
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Mobility
Vr (?,?)
V? (?,?)
V? (?,?)
Electrons
In the coaxial part (? ? /2)
V? 0
Holes
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Electron mobility measurements

• collimated 60keV Am line
• - 1cm x 10? 336 responses
• -averaged, crosstalk corrected
• -chi square optimized simulation
• ?
• 6 Electron mobility par.
• 4 Space Charge par.

0º
Core
Seg1
Seg2
Seg6
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Risetime measurements simulation vs
experiment
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0 60 120 180
240 300 360
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Relative trigger delays
All relative delays of the hit segments relative
to core.
Average delays, corrected for constant fraction
Variance of the residues as function of angle
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Hole mobility measurements
Holes, 7cm depth 30-90 risetime ns of
single events vs angle

• 356keV collimated133Ba line
• Needs no 90Compton coincidence!
• Angle selection via transients
• Single events selection via risetime
• 7cm depth no geometry effect
• ?
• 6 Hole mobility parameters

0º
10º
20º
30º
Core
Seg7
Core
Seg7
Core
Seg7
Core
Seg7
Seg12
Seg12
Seg12
Seg12
Seg8
Seg8
Seg8
Seg8
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Holes, 2.1cm depth
0 60 120 180
240 300 360
Core
250 ns
30-90 risetime ns
200 ns
0 60 120 180
240 300 360
Segments
250 ns
200 ns
30-90 risetime ns
150 ns
0 60 120
angle 240 300 360
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Holes, 2.1cm depth
0 60 120 180
240 300 360
Core
250 ns
30-90 risetime ns
200 ns
0 60 120 180
240 300 360
Segments
250 ns
200 ns
30-90 risetime ns
150 ns
0 60 120
angle 240 300 360
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Holes, 2.1cm depth
Sim. density
0 60 120 180
240 300 360
Core
250 ns
30-90 risetime ns
200 ns
0 60 120 180
240 300 360
Segments
250 ns
200 ns
30-90 risetime ns
150 ns
0 60 120
angle 240 300 360
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• Conclusion
• High agreement between simulation and experiment
  both for electrons holes (?2)
• Position sensitivity limit 1mm
• Full characterization all necessary parameters
  deduced from fast procedures
• Anisotropic Hole mobility model developed and
  verified
• Leads to Non-trivial Space charge enhanced
  anisotropy
• Perfect timing resolution possible if position
  dependent delays are understood
• Outlook
• How does these methods work for Agata?