AGATA: Situationand PerspectivesAGATA: Situationand Perspectives

E.FarneaINFN Sezione di Padova, Italy

OutlineOutline

• Basic concepts: pulse shape analysis and gamma-ray tracking

• Gamma-ray tracking arrays: AGATA and GRETA (in strict alphabetical order)

• Status of AGATA

Why do we need AGATA?Why do we need AGATA?

Problems: complex spectra!

Many lines lie close in energy and the

“interesting” channels are typically the weak ones ...

Our goal is to extract new valuable information on the nuclear structure through the γ-rays emitted following

nuclear reactions

Why do we need AGATA?Why do we need AGATA?

Radioactive Ion Beam facilities will offer exciting physics perspectives under harsh experimental conditions:• High background• Low intensity• Poor beam quality, high v/c

Need:detection efficiencyenergy resolutionbackground suppression

Conventional arrays will not

suffice!

Efficiency vs. ResolutionEfficiency vs. Resolution

With a source at rest, the intrinsic resolution of the detector can be

reached; efficiency decreases with the increasing detector-source

distance.

With a moving source, due to the Doppler effect, also the effective energy resolution depends on the

detector-source distance

Small dLarge d

Large ΩSmall Ω

High εLow ε

Poor FWHMGood FWHM

Compton scatteringCompton scattering

The cross section for Compton scattering in germanium implies quite a large continuous background in the

resulting spectra

Concept of anti Compton shield to reduce such background and increase the P/T ratio

0 500 1000 15000

1000

2000

3000

Unsuppressed

Suppressed

ComptonEdges

From conventional Ge to γ-ray trackingFrom conventional Ge to γ-ray tracking

εph ~ 10%Ndet ~ 100

Using only conventional Gedetectors, too many

detectorsare needed to avoid

summing effects and keep the resolution to good

values

The proposed solution:Use the detectors in anon-conventional way!

Compton Shielded Ge

Ge Sphere

Ge Tracking Array

εph ~ 50%Ndet ~ 1000

θ ~ 8º

θ ~ 3º

θ ~ 1º

Efficiency is lost due to the solid angle covered by the

shield; poor energy resolution at high recoil velocity because of the

large opening angleΩ ~40%

εph ~ 50%Ndet ~ 100

Ω ~80%AGATA and GRETA

Pulse Shape Analysisto decompose

recorded waves

Highly segmented HPGe detectors

··

Identified interaction

points

(x,y,z,E,t)iReconstruction of tracks evaluating permutations of interaction points

EγEγ1

Eγ2

e2

e3

1

3

θ1

θ2

e1

0 2

Digital electronicsto record and

process segment signals

1

2

3

4

Reconstructedgamma-rays

Ingredients of Gamma Tracking

Pulse Shape Calculations andAnalysis by a Genetic AlgorithmPulse Shape Calculations and

Analysis by a Genetic Algorithm

1.130.940.63

0.310.0

z[cm]

0˚ 7.5˚ 15˚ 22.5˚27˚

ϕ

A 0.55B 1.0

r [cm]

C 1.45D 1.9

E 2.35F 2.8

G 3.25H 3.7

net charge signals

-0.2

0

0.2H

GF

E

D C B A

-0.2

0

0.2

100 200 300

rel.

amp

litu

de

100 200 300t [ns]

-1

-0.75

-0.5

-0.25

0

A

BCDEF

GH

-1

-0.75

-0.5

-0.25

0

100 200 300

rel.

amp

litu

de

100 200 300t [ns]

∗

transient signals

•

•

•

•

•

•

• •

••

•

••••

••

•••••••

• •

Base systemof signals

measured or calculated

GAGASets of

interaction points

(E; x,y,z)i

signalsreconstructed

from base

-1

-0.8

-0.6

-0.4

-0.2

0

0 50 100 150 200 250t ns

rel.

ampl

itude

⊕

„fittest“ set

( )EvEqi driftWe/he/h

ρρρ⋅⋅−=

measured signalsWeighting field

method:Weighting fieldmethod:

Reconstructed set of interaction points

(E; x,y,z)i

Th. Kröll, NIM A 463 (2001) 227

In-beam test of PSA: MARS detectorIn-beam test of PSA: MARS detectorCoulex. of 56Fe at 240 MeV on 208Pb, v = 0.08c

Corrected using pointsdetermined with aGenetic Algorithm

Corrected using center of crystal

one detectorwith ∆θ ≈ 22°

Corrected using center of segments

24 detectorswith ∆θ ≈ 9°

Eγ (keV)

Position resolution 5 mm FWHM

β1

βcos(θ)1EE2

Labγ

CMγ

−

−=

FWHM16.5 keV

FWHM6.3 keV

FWHM4.5 keV

recoil

Similar result from an experiment done with the GRETA detector

Best Pulse Shapes searchBest Pulse Shapes search• Search the best χ2 for pulse shapes in the reference base• The pulse shapes associated to one point in the reference

base are choosen as sample• The χ2 of the sample is calculated for all the points in the

reference base• The results obtained for the in-beam experiment are quite

similar to those obtained with a genetic algorithm

r φ

z

r1

φ1 z1

r2 φ2

z2

e1 e2

Best pulse shapes searchGenetic algorithm

16 keV Raw

F = 1

F = 2

F = 3

R.Venturelli, Munich PSA meeting,

September 2004

γ-ray trackingγ-ray trackingPhotons do not deposit their energy in a continuous track, rather they lose it in discrete steps

A high multiplicity eventEγ=1.33MeV, Mγ=30

One should identify the sequence of interaction points belonging to each individual photon

Tough problem! Especially in case of high-multiplicity events

Tracking algorithmsTracking algorithms

( )iii

ii

ii EEe

cmEE

E γγγ

γγ

θ−=

−+= −

−

−1

20

1

1

cos11

Basic ingredient: Compton scatteringformula

• Clustering• Clustering + forward

tracking• Backtracking• Probabilistic tracking• Fuzzy tracking

Several algorithmsare available:

Fuzzy tracking (C. Rossi Alvarez, Padova)

0. Fuzzification/ Implementation of Linguistic rules

1. Identification of the 1st hit interactionFor each i,j deposition pair having medium-big scattering angle OR medium big energy deposition fraction ei/Eγ apply fuzzy rules to find out if i can be 1st ( cannot be 2nd)

2. Fuzzy IterativeSelfOrganizingDataAnalysisTechniquesAlgorithm cluster creationaround 1st hit

Pattern recognition method based on physical distances

3. Missed 1st hits: small angle AND small energy depositionrecovery procedure

4. Fuzzy Cluster Validationselection criteria : energy balance f(Eγ – Efuzzy cluster)

Benefits of the γ-ray trackingBenefits of the γ-ray tracking

scarce

good

Def

init

ion

of t

he

phot

on d

irec

tion

Dop

pler

cor

rect

ion

capa

bilit

yDetector

Segment

Pulse shapeanalysis

+

tracking γ

AGATAAGATA• High efficiency and P/T

ratio.• Good position resolution

on the individual γinteractions in order to perform a good Doppler correction .

• Capability to stand a high counting rate. 180 hexagonal crystals 3 shapes

60 triple clusters all equalInner radius 24 cmAmount of germanium 374 kgSolid angle coverage 79 %6480 segmentsEfficiency at 1MeV: 39% (Mγ=1), 25% (Mγ=30)Peak/Total: 53% (Mγ=1), 46% (Mγ=30)

Pulse shape analysis+

γ-ray tracking

Geodesic Tiling of Sphere using 60–240 hexagons and 12 pentagons

60 80 120110

150 200 240180

Building a Geodesic Ball (1)Building a Geodesic Ball (1)

Start with aplatonic solide.g. an icosahedron

On its faces, draw a regular pattern of triangles grouped as hexagons and pentagons.E.g. with 110 hexagons and (always) 12 pentagons

Project the faces on the enclosing sphere; flatten the hexagons.

Building a Geodesic Ball (2)Building a Geodesic Ball (2)Al capsules 0.4 mm spacing

0.8 mm thickAl canning 2 mm spacing

2 mm thick

A radial projection of thespherical tiling generatesthe shapes of the detectors.Ball with 180 hexagons.

Space for encapsulation andcanning obtained cutting thecrystals. In the example 3 crystals form a triple cluster

Add encapsulation and part of the cryostats for realistic MC simulations

Building a Geodesic Ball (3)Building a Geodesic Ball (3)

The Monte Carlo code for AGATAThe Monte Carlo code for AGATA

• Based on Geant4 C++ classes• Command-line UI with built-in commands to

change the relevant parameters of the simulation

• Geodesic tiling polyhedra handled via a specially written C++ class

• Relevant geometry parameters read from file (generated with an external program)

• Possibility to simulate the ideal Ge-shell

The Monte Carlo code for AGATAThe Monte Carlo code for AGATA

• Possibility to choose the treatment of the interactions for γ-rays (including Rayleigh scattering)

• Compton profile of the electron can be optionally considered

• Polarized photons can be optionally treated• Event generation suited for in-beam

experiments• Possibility to consider events with variable

multiplicity by decoding an external file

Class structure of the programClass structure of the programAgata

*AgataRunAction

*AgataEventAction

AgataPhysicsList

AgataVisManager

AgataSteppingAction

*AgataAnalysis Agata

GeneratorAction

CSpec1DAgata

GeneratorOmegaAgata

SteppingOmega

*AgataDetector

Construction

*AgataDetector

Shell

*AgataDetectorSimple

*AgataSensitiveDetector

*AgataDetectorArray

AgataHitDetector

CConvexPolyhedronMessenger classes are not shown!Messenger classes are not shown!

* Possibility to change parameters via a messenger class

*AgataDetectorAncillary

CSpec2D*AgataEmitted

AgataEmitter

*AgataExternalEmission

*AgataExternalEmitter

*AgataInternalEmission

*AgataInternalEmitter

Two candidate configurationsGe crystals size:Length 90 mm

Diameter 80 mm

120 hexagonal crystals 2 shapes30 quadruple-clusters all equalInner radius (Ge) 18.5 cmAmount of germanium 230 kgSolid angle coverage 78 % 4320 segmentsEfficiency: 37% (Mγ=1) 22% (Mγ=30)Peak/Total: 52% (Mγ=1) 44% (Mγ=30)

180 hexagonal crystals 3 shapes60 triple-clusters all equalInner radius (Ge) 24 cmAmount of germanium 374 kgSolid angle coverage 79 %6480 segmentsEfficiency: 39% (Mγ=1) 25% (Mγ=30)Peak/Total: 53% (Mγ=1) 46% (Mγ=30)

Expected PerformanceExpected PerformanceResponse function

Absolute efficiency value includes the effects of the tracking algorithms!Values calculated for a source at rest.

Effect of the recoil velocityEffect of the recoil velocityThe comparison between spectra obtained knowing or not knowing

the event-by-event velocity vector shows that additional

information will be essential to fully exploit the concept of

tracking

β=20%

0.30.72.4∆β (%)

0.30.62σdir(degrees)

0.30.51.5δs(cm)

5020 5β (%)

AGATA DetectorsAGATA Detectors

Hexaconical Ge crystals90 mm long80 mm max diameter36 segmentsAl encapsulation:

0.4 mm spacing0.8 mm thickness

37 vacuum feedthroughs

3 encapsulated crystals111 preamplifiers with cold FET~230 vacuum feedthroughsLN2 dewar, 3 liter, cooling power ~8 watts

Germany & Italy ordered 3 symmetric encapsulated crystals (2 delivered).Cryostat will be built by CTT in collaboration with IKP-Köln.

AGATA/GRETA Prototypes Tapered regular hexagonal shapeTaper angle 10ºDiameter (back) 80 mmLength 90 mmWeight 1.5 kgOuter electrode 36-fold segmented

Encapsulation of crystal in a permanent vacuum is essential for highly segmented Ge detectors

Courtesy Canberra-Eurisys

AGATA Symmetrical PrototypeAGATA Symmetrical Prototype

Delivered summer 2004.Tested using

modified MINIBALL cryostat.

Courtesy of J.Eberth and D.Weisshaar, IKP Köln

0,00

0,50

1,00

1,50

2,00

2,50

Reihe1

Reihe2

Segment specifications

Guaranteed FWHM at 1.3MeV : <2.30keV, mean < 2.1keVat 60keV : <1.35keV, mean < 1.15keV

Expected FWHM at 1.3MeV : mean < 2.05keV at 60keV : <1.00keV

FWHM at 1.3MeV

FWHM at 60keV

Mean(1.3MeV)=1.99keV

Mean(60keV)=1.14keV

Core specification

Guaranteed at 1.3MeV: 2.35keVat 122keV: 1.35keV

Core FWHM: at 1.3MeV : 2.10keVat 122keV : 1.20keV

Segmentation of AGATA crystalsThe impact of effective segmentation

0 1 2 3 3.8 0 1 2 3 3.80

10

geometrical segmentation

tapering angle ~ 8°0 1 2 3 3.8

0

10

z [cm

]

0 1 2 3 3.80

10

r [cm]

PreamplifiersPreamplifiers• Discrete hybrid solution

developed in collaboration between Milano, Köln, GANIL, Padova and GSI

• Cold FET• Differential output to the

digitizers• Fast reset to limit the

effects of signal saturation• ASIC solution is being

investigated (Saclay)

Data rates in AGATA @ 10 kHz singles

100 B/ev

1 MB/s

200 MB/s

1.5 ··· 7.5 kB/ev

~ 20 MB/s

36+1 7.5 kB/event80 MB/s

~ 200 B/segment~ 2 MB/s

100 Ms/s14 bits

Pulse ShapeAnalysis

Event Builder

γ-rayTracking

HL-Trigger, StorageOn Line Analysis

< 100 MB/s

SEGMENT

GLOBAL

Energy &Classification

5*n max. 200 MB/s

save 600 ns ofpulse rise time

E, t, x, y, z,...DETECTOR

LL-Trigger

Suppression /Compression

ADC

Preprocessing+-

GL-Trigger

GL-Trigger to reduce event rate to whatever value PSA will be able to manage

0.1 ms/ev

Electronics and DAQ for AGATAElectronics and DAQ for AGATAGTS …detector

Preamps

Digitizers

detector

Preamps

DigitizersDigita

lDigita

l

preamplifi

er

preamplifi

er

Fully synchronous system with global100 MHz clock and time-stampdistribution (GTS)

Digitizers: 100 Ms/s, 14 bitOptical fiber read-out of full datastream to pre-processing electronics

Localprocessing

Localprocessing

7.4 GB/s/det

20 MB/s/det

Local processing triggered by Ge commoncontact. Determine energy and isolate ~ 600 ns of signal around rise-time

Buffers of time-stamped local events sentto PSA. CPU power needed ~106 SI95

PSA PSA

1 MB/s/det

On line…Storage …

Tracking

EventBuilder

< 200 MB/sTrigger-less system. Global trigger possible.Global event builder and software trigger

On-line gamma-ray tracking

Control and storage (~1 TB/year), …

AGATAAGATA(Advanced GAmma Tracking Array)

4π γ-array for Nuclear Physics Experimentsat European accelerators

providing radioactive and high-intensity stable beamsMain features of AGATA

Efficiency: 39% (Mγ=1) 25% (Mγ=30)today’s arrays ~10% (gain ~4) 5% (gain ~1000)

Peak/Total: 53% (Mγ=1) 46% (Mγ=30)today ~55% 40%

Angular Resolution: ~1ºFWHM (1 MeV, v/c=50%) ~ 6 keV !!!today ~40 keV

Rates: 3 MHz (Mγ=1) 300 kHz (Mγ=30)today 1 MHz 20 kHz

180 large volume 36-fold segmented Ge crystals packed in 60 triple-clusters Digital electronics and sophisticated Pulse Shape Analysis algorithms allowOperation of Ge detectors in position sensitive mode γ-ray trackingDemonstrator ready by 2007; Construction of full array from 2008 New members!

AGATA OrganisationAGATA OrganisationSteering Committee ASCChair: Marcello Pignanelli

14 representatives of 12 EU countries

Management Board AMBPM: John Simpson

and the responsibles of the 7 Working Groups

J.Eberth

DetectorModule

R.Krücken

DetectorPerformance

D.Bazzacco

Data Processing

G.Duchêne

Design &Infrastructure

A.Gadea

AncillaryDetectorsand their Integration

J.Nyberg W.Korten

Simulationand DataAnalysis

EUContact

AGATA Working TeamsPreamplifiers

Detector and cryostat

Pulse ShapeAnalysis

Detectorcharacterisation

Mechanical design

Infrastructure

R & D otherdetectors

Impact on performance

Electronics and DAQintegration

Mechanical integration

Devices for key Experiments

Exp. Simulation

Gamma-ray tracking

Data base

Data analysis

Digitisation

Pre-processing algorithms

Pre-processinghardware

Global clock and trigger

Data acquisition

Run-control + GUI

Illegal Alien sneaked into the Management!!!

The Management

Status of AGATA• MoU for demonstrator phase (2003-2007)

signed by national institutions.• Structure of collaboration defined:

– ASC, AMB, AWG, AWT• First 3 encapsulated crystals and cryostat

ordered by Italy(1) and Germany(2)• First 2 capsules delivered and successfully

tested with a test cryostat• Symmetric triple-cluster expected to be ready

beginning 2005, will be assembled, tested and then dismounted for further tests of the individual crystals

Status of AGATA• Final asymmetric crystal geometry defined August

2004• Asymmetric crystals ordered by Italy (2);

France should place orders by end 2004 (2)• Funds available for a total of 9 asymmetric capsules• Sweden and Turkey applied each for a full asymmetric

cluster• Demonstrator ready (with full electronics and DAQ

for real-time operation) by the end of 2006.• Tests and first experiments in 2007• Construction of AGATA in phases, starting from 2008

(if demonstrator is successful!)• Major problem: cost of detectors

SummarySummary

• Gamma-ray tracking arrays will be very powerful tools to extract valuable information for nuclear structure and reaction studies

• Work continues ...