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Semiconductor detectors
Band gap between
valence and conduction
band:
Ge: 0.7 eV
Si: 1.1 eV
GaAs: 1.4 eV
Diamond: 5.5 eV
Ionisation energy to
create electron-hole pairs
is proportional to band
gap, but 2-3 higher.
Energy, momentum
conservation
=> phonon excitation
(chapter Fano factor)
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Ge-detectors
production of
high purity germanium
eN
VW b2
Thickness of depletion zone
charge carrier concentration
Ge: N~10-12 per atom
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Detector geometries
High voltage
and type of
material
determines
drift direction of
electrons and
holes
Ge-detectors
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Electric field and potential
in HPGe detector
coaxial
Ge-detectors
Electric field
Electric field
potential
potential
hexagonal
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different drift velocities of electrons and holes
two position dependent components determine signal
basic for pulse shape analysis
Elektronen
Ge-detectors
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Standard HPGe-detector
Ge-detectors
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Gammasphere
110 HPGe detectors
and anti-Compton shield
improved P/T~0.6
Ge-detectors
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High purity Ge-crystals provide excellent properties for g-spectroscopy: • Energy range: 20 keV – 5 MeV• high energy resolution: DE/E ~ 0.16 % or 2 keV @ 1.33 MeV
• Efficiency is limited by size of single Ge crystal
Development: University of KölnKFA-Jülich, EURISYS
Composite CLUSTER detector - seven large hexagonal tapered Ge detectors- encapsulated Ge crystals- closely packed in a common cryostat - common BGO escape-suppression shield - increased total-absorbtion efficiency- at 5 MeV the efficiency is doubled- highest peak to total ratio 61 percent
Composite Ge-detectors
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EUROBALL-spectrometer
239 single Ge crystals
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EUROBALL seen from a g-ray
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MINIBALL
6 Fold
MINIBALL
12 Fold
AGATA
Prototype
36 Fold
Segmented Ge-detectors
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O Composite segmented Ge-detectors
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REX-ISOLDE @ CERN
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ph ~ 10%
Ndet ~ 100
Combination:
• Segmented crystals
• Digital Electronics
• Pulse-shape analysis
• Tracking of g-rays
Compton suppression
Germanium Shell
Ge Tracking Array
ph ~ 50%
Ndet ~ 1000
ph ~ 50%
Ndet ~ 100
q ~ 8º
q ~ 3º
q ~ 1º
Larger opening angle -
=> lower energy
resolution at large
velocities, broadening
Idea of g-ray Tracking
Too many detectors at
large distance (to
reduce multiple hits)
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New g-ray detection method
• 6660 high-resolution digital electronics channels
• Coupling to ancillary detectors for added selectivity
180 hexagonal crystals 3 shapes
60 triple-clusters all equal
Inner radius (Ge) 23.5 cm
Amount of germanium 362 kg
Solid angle coverage 82 %
36-fold segmentation 6480 segments
Singles rate ~50 kHz
Efficiency: 43% (Mg=1) 28% (Mg=30)
Peak/Total: 58% (Mg=1) 49% (Mg=30)
Advanced GAmma Tracking Array
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Ingredients of Gamma–Ray Tracking
Pulse Shape Analysisto decompose
recorded waves
··
Identified interaction points
(x,y,z,E,t)i
Reconstruction of tracks evaluating permutations
of interaction points
Digital electronicsto record and
process segment signals
1
23
4
Reconstructedgamma-rays
Highly segmented HPGe detectors
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Asymmetric AGATA Tripel Cryostat-integration of 111 high resolution spectroscopy channels
-cold FET technology for all signals
Challenges:
-mechanical precision
-microphonics
-noise, high frequencies
-LN2 consumption
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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
CoreSeg1
Seg2
Seg6
10º
CoreSeg1
Seg2
Seg6
20º
CoreSeg1
Seg2
Seg6
30º
CoreSeg1
Seg2
Seg6
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Hole mobility measurements
Collimator-356keV collimated133Ba line
-Needs no 90°Compton coincidence!
-Angle selection via transients
-Single events selection via risetime
-7cm depth: no geometry effect
6 Hole mobility parameters
0º
Core Seg7
Seg12
Seg8
10º
Core Seg7
Seg12
Seg8
20º
Core Seg7
Seg12
Seg8
30º
Core Seg7
Seg12
Seg8
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Pulse Shape Analysis Concept
B4 B5B3
C4 C5C3
CORE
A4 A5A3
C4
D4
E4 F4
A4
B4
x
y
z = 46 mm791 keV deposited in segment B4
measured
Library
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Pulse Shape Analysis Concept
B4 B5B3
C4 C5C3
CORE
A4 A5A3
C4
D4
E4 F4
A4
B4
x
y
z = 46 mm791 keV deposited in segment B4
(10,10,46)
measuredcalculated
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Pulse Shape Analysis Concept
B4 B5B3
C4 C5C3
CORE
A4 A5A3
C4
D4
E4 F4
A4
B4
x
y
z = 46 mm791 keV deposited in segment B4
(10,15,46)
measuredcalculated
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Pulse Shape Analysis Concept
B4 B5B3
C4 C5C3
CORE
A4 A5A3
C4
D4
E4 F4
A4
B4
x
y
z = 46 mm791 keV deposited in segment B4
(10,20,46)
measuredcalculated
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Pulse Shape Analysis Concept
B4 B5B3
C4 C5C3
CORE
A4 A5A3
C4
D4
E4 F4
A4
B4
x
y
z = 46 mm791 keV deposited in segment B4
(10,25,46)
measuredcalculated
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Pulse Shape Analysis Concept
B4 B5B3
C4 C5C3
CORE
A4 A5A3
C4
D4
E4 F4
A4
B4
x
y
z = 46 mm791 keV deposited in segment B4
(10,30,46)
measuredcalculated
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Pulse Shape Analysis Concept
Result of Grid Searchalgorithm
R. VenturelliB4 B5B3
C4 C5C3
CORE
A4 A5A3
C4
D4
E4 F4
A4
B4
x
y
z = 46 mm791 keV deposited in segment B4
(10,25,46)
measuredcalculated
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g-spectrometer and ancillary detectors
Detection of light charged particles
Separation of different
light charged particles
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Experimental set-up: T-REX & MINIBALL
beam
MINIBALL
• 24 HPGe
• 6-fold segmented
• ≈ 3% @ 1.3 MeV
beam
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Scintillator detectors for light charged particles
Microball inside Gammasphere
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Energy resolution and `kinematic correction`
g- energy resolution is
determined by:
• Doppler effect and
opening angle of
Ge-detectors
• energy loss in target
(-> thin targets)
• kinematic of recoiling
nuclei (direction and
velocity)
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Scintillators for neutron detection