Semiconductor detectors - Universität zu Köln · Semiconductor detectors Band gap between valence...
Transcript of Semiconductor detectors - Universität zu Köln · Semiconductor detectors Band gap between valence...
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)
Ge-detectors
production of
high purity germanium
eN
VW b2
Thickness of depletion zone
charge carrier concentration
Ge: N~10-12 per atom
Detector geometries
High voltage
and type of
material
determines
drift direction of
electrons and
holes
Ge-detectors
Electric field and potential
in HPGe detector
coaxial
Ge-detectors
Electric field
Electric field
potential
potential
hexagonal
different drift velocities of electrons and holes
two position dependent components determine signal
basic for pulse shape analysis
Elektronen
Ge-detectors
Standard HPGe-detector
Ge-detectors
Gammasphere
110 HPGe detectors
and anti-Compton shield
improved P/T~0.6
Ge-detectors
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
EUROBALL-spectrometer
239 single Ge crystals
EUROBALL seen from a g-ray
MINIBALL
6 Fold
MINIBALL
12 Fold
AGATA
Prototype
36 Fold
Segmented Ge-detectors
O Composite segmented Ge-detectors
REX-ISOLDE @ CERN
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)
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
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
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
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
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
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
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
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
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
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
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
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
g-spectrometer and ancillary detectors
Detection of light charged particles
Separation of different
light charged particles
Experimental set-up: T-REX & MINIBALL
beam
MINIBALL
• 24 HPGe
• 6-fold segmented
• ≈ 3% @ 1.3 MeV
beam
Scintillator detectors for light charged particles
Microball inside Gammasphere
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)
Scintillators for neutron detection