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