Modern Arrays for γ and particles Detection

Modern Arrays for γ and particles Detection

ƒ Basic concepts of radiation interaction & detection

ƒ Ge Arrays: EUROBALL & AGATA

ƒ Ancillary Devices

γ -ray interaction

γ γ

σ σ σ

γ γ

E Z

E E Z E n

Z

pp C

n ph

ln ln

5 4

2 5 . 3

≈

≈

−

=

≈

Compton scattering angular distribution

) cos 1 )(

/ (

1 ²

'

γ θ

γ

γ = + −

c m E E E

e E_γ´

E_γ incident γ

662 keV 482 keV

FWHM=1keV

FWHM=40 keV

Ge

NaTl

E_γ [keV]

Counts

Energy resolution Timing

The detector performances depend on the the detector properties

efficiency

Ge

Ge detector

anti-Compton (BGO) + We detect recoil electrons

and NOT photons !

VETO

GAMMA -DETECTOR Systems

ƒ Ge detector + BGO shields

ƒ Multiplicity filter (BGO or BaF2)

ƒ Si detectors for particles (p, α, d)

ƒ RMS, PPAC (for recoil detection)

EUROBALL

4π Ge detector Array

EUROBALL @ IRES (Strasbourg)

30 TAPERED GE-DETECTORS

26 CLOVER

GE-DETECTORS

BEAM LINE

15 CLUSTER GE-DETECTORS

EUROBALL

(239 Ge Crystals)

ε ≈ 60%

HPGE CLOVER

ε ≈ 35%

HPGE CLUSTER Composite Ge detectors

EUROBALL M_γ=30, v/c=2%

ε_γ ≈ 6.5 % P/T ≈ 40 %

Ω ≈ 40%

E_γ=1.3 MeV, SE_γ = 70 keV, M_γ = 30, v/c=2% Full Ball: Ge+BGO ≈ 4π

15%

150%

Cluster Ge detector

Solution:

composite Ge detectors Effetto Doppler

) sin

1

0( γ

γ

γ

θ

c E v

E = +

Doppler broadening

θ θ

γ

γ = ∆

∆ 2 ₀ sin sin

c E v E

Ge detectors with large opening angle suffer of a considerable

energy deterioration

single Ge

composite Ge

30Si+¹²⁴Sb → ¹⁴⁹Gd E_beam=158MeV

v/c=2.1%

Resolving power

F

F

T

P E

R SE  





 



 ×

= ∆

γ γ

=

=

=

∆

=

F T

P E SE

γ γ

γ-ray energy resolution Peak–to-total (Compton)

M

P

F >=

<

= Ω

Ge

P

N ε

array capability of

identifying weak γ cascades

Observation Limit

Year

Observational Limit

γ-ray energy spacing

Measured fold

Total photopeak efficiency

Light ions

scintillators detectors

Light ions

Ge detectors: 1 γ

Heavy Ions

Ge detectors: 1 γ

Heavy Ions

Ge detectors: ≥ 2 γ

Heavy Ions

Ge detectors: ≥ 3 γ

2.5 tons

R_inner = 17 cm, R_outer = 26 cm Ω ≈ 77%

ε ^≈ 40% (Mγ=1), 20% (Mγ=30) P/T ≈ 65% (Mγ=1), 50% (Mγ=30) FWHM ≈ 1 keV (1 MeV, source)

≈ 6 keV (1 MeV, v/c ≈50%) instead of 40 keV at present !!

FWHM [keV]

v/c [%]

ƒ Digital electronics (to record and process segments signals)

ƒ Pulse Shape Analysis (to extract position and energy of interaction)

ƒ Tracking Analysis (to reconstruct γ-rays tracks from interaction points)

based on

position sensitive Ge

AGATA

Advanced Gamma Tracking Array

192 segmented Ge detectors

(36segments each) ⇒ 6780 segments 180 hexagonal Ge in 60triple clusters

12 pentagonal Ge

Construction ≈ 8 y, Cost ≈ 40 M€

AGATA: ^{Advanced Gamma Tracking Array}

• •

• •

Highly segmented HPGe detectors

180 crystals configuration

Irregular hexagonal crystals 3 shapes 60 triple-clusters identical

Radius 23,5 cm

Solide angle Ge 82%

Nb of segments 6480

Nb of channels 6660

Pulse shape analysis to identify

interaction points

Eγ

Eγ₁

Eγ₂ e₂

e₃

1

3 θ₁

θ₂ e₁

0 2

(x,y,z,E,t)_i

0 5 10 15 20 25

5 15 25 35 45

v/c (%)

FWHM (keV)

Köln September 2005:

1⁰Triple-cluster test

Demonstrator 6Triple-clusters :

ε∼ 5 - 3 % Ready by 2007

(LNL-GANIL)

γ

reconstruction of tracks via Compton scattering

analysis

ε∼ ^{40 - 20 % ( M}_γ^{=1 — M}_γ⁼³⁰⁾

(10 – 5%)

Count rate ~ 3 MHz - 300 kHz (1 MHz - 20 kHz)

Ancillary Detectors

ƒ Innerball: calorimeter

ƒ Hector: high - energy γ-rays

ƒ Diamant: charged particles

ƒ Neutron wall: n identification

ƒ Recoil filter: evaporation residua

Inner Ball

(143 BGO detectors)

γ -multiplicity M

→ I γ -sum energy ΣE

→ E*

ΣE γ→E*

M_γ → I(h) Filtro del

canale di reazione

Full Ball: Ge + InnerBall ≈ 4π

40% 60%

Hector

(8 BaF₂ detectors)

∆Eγ/Eγ (⁶⁰Co) ≈ 11%

∆T ≈ 1 ns

εε_phph (15 MeV(15 MeV) ) ≈≈ 10%10%

LED gain monitor

14cm × 18 cm

1 10 100 1000 10000 100000

a) ^total

γ gate

Counts [arb. unit]

0 2 4 6 8 10 12 14 16 18 20

E_γ [MeV]

GDR 126

Ba

E_γ [MeV]

Diamant

(84 CsI(Tl) detectors)

light charged particle detector array

4π array

α

p p α

ε_proton ≈ 70%, ε_α ≈ 50%

Operating mode:

DIAMANT alone: particle-xn channels

DIAMANT + Ge : particle-xn + xn channels

Neutron Wall

(50 detectors ~ 1π)

Important in the study of neutron deficient nuclei

(one looks for the evaporation of 1-2 n)

Liquid Scintillators BC501A Total Volume ~ 151 litri

Basic Principle:

ƒ elastic scattering n – p (of the liquid scintillator)

ƒ separation between n and γ with TOF + pulse shape (ZCO time)

Recoil Filter Detector

(50 detectors ~ 1π)

Importante in the study

of heavy nuclei where one has 1. Only few evaporation residua 2. Large fraction of fission

3. Large amount of particle emission

Residues identification & v/c determination ε ~ 65%

18 elements of mylar foils (0.5 -2 µm):

Recoiling ions produce from the mylar

electrons accelerated from 20 kV and focused on plastic scintillators

# elettrons ∝ energy released by the ion

beam

counts

E_γ [keV]

mean velocity correction

<β> ~ 2.8%

true velocity correction