AGATA: Statusand Perspectives

AGATA: Statusand Perspectives

E.FarneaINFN Sezione di Padova, Italy

on behalf of the AGATA Collaboration

OutlineOutline

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

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

• Status of AGATA

European -ray detection systems

European -ray detection systems

TESSA ESS30

EUROGAM

GASP

EUROBALL III

EUROBALL IV

1980 1986 1992 1996

Composite & encapsulated detectors

Composite & encapsulated detectors

CLOVEREB-CLUSTER

Why do we need AGATA?Why do we need AGATA?Our goal is to extract new valuable

information on the nuclear structure through the -rays emitted following

nuclear reactions

Problems: complex spectra!

Many lines lie close in energy and the

“interesting” channels are typically the weak

ones ...

Neutron rich heavy nuclei (N/Z → 2)• Large neutron skins (r-r→ 1fm)• New coherent excitation modes• Shell quenching

132+xSn

Nuclei at the neutron drip line (Z→25)• Very large proton-neutron asymmetries• Resonant excitation modes• Neutron Decay

Nuclear shapes• Exotic shapes and isomers • Coexistence and transitions

Shell structure in nuclei• Structure of doubly magic nuclei • Changes in the (effective) interactions

48Ni100Sn

78Ni

Proton drip line and N=Z nuclei• Spectroscopy beyond the drip line• Proton-neutron pairing• Isospin symmetry

Transfermium nucleiShape coexistence

Challenges in Nuclear Structure

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

• Low intensity• High background• Large Doppler broadening• High counting rates• High -ray multiplicities

High efficiencyHigh sensitivityHigh throughputAncillary detectors

FAIRSPIRAL2SPESREX-ISOLDEMAFFEURISOLHI-Stable

Harsh conditions!Need instrumentation with

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 Small

High Low

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

P/T~30%

P/T~50%

From conventional Ge to -ray tracking

From conventional Ge to -ray tracking

ph ~ 10%

Ndet ~ 100

Using only conventional Ge detectors, 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

ph ~ 50%

Ndet ~ 1000

~ 8º

~ 3º

~ 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 angle ~40%

ph ~ 50%

Ndet ~ 100

~80%AGATA and GRETA

Ingredients of Gamma Tracking

Pulse Shape Analysisto decompose

recorded waves

Highly segmented

HPGe detectors

·

·

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

2

3

4

Reconstructed

gamma-rays

Arrays of segmented Ge detectors(for Doppler correction)

MINIBALL triple-clusterswith 6 and 12 fold segmentation

Segmented Germanium Array (SeGA) with 32-fold segmentation

EXOGAM segmented cloverswith 4x4 fold segmentation

Pulse Shape Calculations andAnalysis by a Genetic

Algorithm

Pulse Shape Calculations andAnalysis by a Genetic

Algorithm

net charge signals

transient signals

Base system of signals

measured or calculated

GAGASets of

interaction points

(E; x,y,z)i

measured signals

signalsreconstructed

from base

Reconstructed set of interaction points

(E; x,y,z)i

„fittest“ set

Weighting fieldmethod:

Weighting fieldmethod:

Th. Kröll, NIM A 463 (2001) 227

In-beam test of PSA: MARS detector

In-beam test of PSA: MARS detector

Corrected using pointsdetermined with a Genetic Algorithm

Corrected using center of crystal one detectorwith 22°

Corrected using center of segments 24 detectors

with 9°

E (keV)

Position resolution 5 mm FWHM

Coulex. of 56Fe at 240 MeV on 208Pb, v = 0.08c

β1

βcos(θ)1EE

2

Labγ

CMγ

FWHM16.5 keV

FWHM6.3 keV

FWHM4.5 keV

Similar result from an experiment done with the GRETA detector

recoil

MC limit assuming

5 mm FWHM position

resolution:4.2 keV

An alternative approach: Grid search

An alternative approach: Grid search

r

z

r1

1 z1

r2 2

z2

e1 e2

R.Venturelli, Munich PSA meeting,

September 2004

Raw

F = 1

F = 2

F = 3

16 keV

Genetic algorithm Best pulse shapes search

• Search the best 2 for pulse shapes in the reference base

• The pulse shapes associated to one point in the reference base are choosen as sample

• The 2 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

Other approaches (neural networks, wavelets, etc.) are currently attempted within the collaboration

-ray tracking-ray tracking

A high multiplicity eventE=1.33MeV, M=30

Photons do not deposit their energy in a continuous track, rather they lose it in discrete steps

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

Tough problem! Especially in case of high-multiplicity events

Interaction of photons in germanium

Interaction of photons in germanium

Mean free path determines size of detectors:

( 10 keV) ~ 55 m(100 keV) ~ 0.3 cm(200 keV) ~ 1.1 cm(500 keV) ~ 2.3 cm( 1 MeV) ~ 3.3 cm( 2 MeV) ~ 4.5 cm( 5 MeV) ~ 5.9 cm(10 MeV) ~ 5.9 cm

Tracking algorithmsTracking algorithms

Basic ingredient: Compton scatteringformula

1N

1 n

2PE

P2

0

E

EP

'P

1

1

E'

1E

22EE2

cosθ1cm

E1

EE

1201

1201cosθ

EE

γ'γ'

nn

eeN

nii

N

nii

Reconstruction of multi-gamma events

Reconstruction of multi-gamma events

Analysis of all partitions of measured points is not feasible:Huge computational problem(~1023 partitions for 30 points) Figure of merit is ambiguous the total figure of merit of the “true” partition not necessarily the minimum

1 – Cluster (forward) tracking

2 – Backtracking

3 – Other approaches

(fuzzy tracking, etc.)

1. Create cluster pool => for each cluster, E0 = cluster depositions

2. Test the 3 mechanisms 1. do the interaction points satisfy

the Compton scattering rules ?

2. does the interaction satisfyphotoelectric conditions (e1,depth,distance to other points) ?

3. do the interaction points correspondto a pair production event ?

E1st = E – 2 mec2

3. Select clusters based on 2

1N

1 n nγ

Posγ'

n

2

E

EEW

2γ'

Forward tracking(G.Schmid, 1999; mgt implementation by D.Bazzacco, Padova)

Backtracking (J. Van der Marel et al., 1999)

Photoelectric energy deposition is approximately independent of incident energy and is peaked around100-250 keV

83% 87%

=> interaction points within a given deposited energy interval (emin < ei < emax) will be considered as the last interaction of a fully absorbed gamma

BacktrackingB. Cederwall, L. Milechina, A. Lopez-Martens

2. Find closest interaction j to photoelectric interaction i

3. Find incident direction from incident + scattered energies

4. Find previous interaction k or source along direction

1. Create photoelectric interaction pool: emin< ei < emax

prob. for photoelectric interaction > Pphot,min

distance between interaction points < limit

cos(energy) - cos(position) < limitprob. for Compton interaction > Pcomp,min

distance between interaction points < limit

cos = 1 – mec2(1/Esc –1/Einc)

Einc = ei + ej, Esc = ei

Einc = ei+ej+ek

Esc = ei+ej

the last points of the sequence are low energy and close to each other bad position resolution and easily packed together

Benefits of the -ray tracking

Benefits of the -ray tracking

scarce

good

Defin

itio

n o

f th

e

photo

n d

irect

ion

Dop

ple

r co

rrect

ion

cap

abili

tyDetector

Segment

Pulse shapeanalysis

+

tracking Energy (keV)

v/c = 20 %

AGATAAGATA• High efficiency and

P/T ratio.• Good position

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

• Capability to stand a high counting rate. Pulse shape

analysis+

-ray tracking

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)

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

Al capsules 0.4 mm spacing0.8 mm thick

Al canning 2 mm spacing2 mm thick

60 80 110 120

150 180 200 240

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

The Monte Carlo code for AGATAThe Monte Carlo code for AGATA

• Based on Geant4 C++ classes• Geodesic tiling polyhedra handled via a

specially written C++ class• Relevant geometry parameters read from

file (generated with an external program)• Possibility to choose the treatment of the

interactions for -rays (including Rayleigh scattering, Compton profile and linear polarization)

• Event generation suited for in-beam experiments

Class structure of the program

Class structure of the program

Agata

*AgataRunAction

*AgataEventAction

AgataPhysicsList

AgataVisManager

AgataSteppingAction

*AgataAnalysis

AgataGeneratorAction

CSpec1D

AgataGeneratorOmega

AgataSteppingOmega

*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

GRETA vs. AGATA

120 hexagonal crystals 2 shapes30 quadruple-clusters all equalInner radius (Ge) 18.5 cmAmount of germanium 237 kgSolid angle coverage 81 % 4320 segments

Efficiency: 41% (M=1) 25% (M=30)Peak/Total: 57% (M=1) 47% (M=30)

Ge crystals size:Length 90 mm

Diameter 80 mm

180 hexagonal crystals 3 shapes60 triple-clusters all equalInner radius (Ge) 23.5 cmAmount of germanium 362 kgSolid angle coverage 82 %6480 segments

Efficiency: 43% (M=1) 28% (M=30)Peak/Total: 58% (M=1) 49% (M=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 velocity

Effect of the recoil velocity

=20%The 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

s(cm) 1.5 0.5 0.3

dir(degrees) 2 0.6 0.3

(%) 2.4 0.7 0.3

Uncertainty on the recoil direction (degrees)

AGATA/GRETA Prototypes

MINIBALL-style cryostatused for acceptance tests“standard” preamplifiers

Encapsulation0.8 mm Al walls0.4 mm spacing

36-fold segmented, encapsulated detector36-fold segmented, encapsulated detector

Segmentation of AGATA crystals The impact of effective segmentation

r [cm]

z [c

m]

geometrical segmentation

tapering angle ~ 8°

0.00

0.50

1.00

1.50

2.00

2.50

Guaranteed FWHM

at 1.33 MeV : < 2.30 keV, mean < 2.1 keVat 60 keV : < 1.35 keV, mean < 1.15 keV

2.01 keV <FWHM> @1.33 MeV

1.03 keV <FWHM> @ 60 keV

Guaranteed FWHM

at 1.33 MeV : 2.35 keVat 122 keV : 1.35 keV

Measured FWHM

at 1.33 MeV : 2.13 keVat 122 keV : 1.10 keV

Energy Resolution(measured with analogue electronics)

The 36 segments Core

The 3 detectors are very similar in performance

A003 (INFN)

AGATA Cryostats

Individual, for tests Triple, for experimentsdifferential-output preamplifiers with fast resetof saturated signals (Milano/Ganil, Köln)

AGATA detector scanning

Liverpool coincidence setup with multileaf collimator

Other system being developedat CSNSM Orsay and GSI

Full scan in 1 mm3 grid almost impossible define characteristic points to calibrate calculations

Main features of AGATA

Efficiency: 43% (M=1) 28% (M=30)today’s arrays ~10% (gain ~4) 5% (gain ~1000)

Peak/Total: 58% (M=1) 49% (M=30)today ~55% 40%

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

Rates: 3 MHz (M=1) 300 kHz (M=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 -ray trackingDemonstrator ready by 2007; Construction of full array from 2008

AGATAAGATA(Advanced GAmma Tracking Array)

4 -array for Nuclear Physics Experimentsat European accelerators

providing radioactive and high-intensity stable beams

Chairperson J.Gerl, Vice Chairperson, N.AlamanosG.deAngelis, A.Atac, D.Balabanski, D.Bucurescu, B.Cederwall,

D.Guillemaud-Mueller, J.Jolie, R.Julin, W.Meczynski, P.J.Nolan, M.Pignanelli, G.Sletten, P.M.Walker

J.Simpson (Project Manager)D.Bazzacco, G.Duchêne, J.Eberth, A.Gadea, W.Korten, R.Krücken, J.Nyberg

AGATA Working GroupsDetectorModuleJ.Eberth

Detector Performance

R.Krücken

DataProcessing

D.Bazzacco

Design andInfrastructure

G.Duchêne

Ancillary detectors and Integration

A.Gadea

Simulation andData Analysis

J.Nyberg

PreamplifiersA.Pullia

Detector and Cryostat

D.Weisshaar

PSAR.Gernhäuser/P.Desesquelles

DetectorCharacterisation

A.Boston

DigitisationP.Medina

Pre-processingI.Lazarus

Global clockand TriggerM.Bellato

Data acquisitionX.Grave

Run Control & GUI

G.Maron

Mechanical designK.Fayz/J.Simpson

InfrastructureP.Jones

R&D on gammadetectorsD.Curien

Electr. and data acq.Ch. Theisen

Impact on performanceM.Palacz

Mechanical integration

Devices for key Experiments

N.Redon

Gamma-rayTracking

W.Lopez-Martens

Experiment simulationE.Farnea

Detector data baseK.Hauschild

Data analysisO.Stezowski

AGATA Teams

AGATA Managing Board

AGATA Steering Committee

AGATA organisation April 2005

EURONS

W.Korten

The Management

Illegal Alien sneaked into the Management!!!

The First Step:The AGATA Demonstrator

Objective of the final R&D phase 2003-2008

1 symmetric triple-cluster5 asymmetric triple-clusters

36-fold segmented crystals540 segments555 digital-channels

Eff. 3 – 8 % @ M = 1

Eff. 2 – 4 % @ M = 30

Full ACQwith on line PSA and -ray trackingTest Sites:GANIL, GSI, Jyväskylä, Köln, LNLCost ~ 7 M €

Status of development• Funding

– a 4 triple-clusters system (12 crystals) secured (almost)– Sweden and Turkey bidding for a triple cluster each

• Detectors– 11 of the 12 detectors ordered– 3 of them (symmetric) delivered and tested– partial coincidence scan for one detector done at Liverpool– first triple cluster being assembled now at Köln– in beam experiment planned end of August at the Köln Tandem with

Miniball (XIA) electronics– delivery of first asymmetric detector by November 2005

• Electronics and DAQ– design frozen at the last AGATA week (Feb. 2005)– development of modules ongoing (hardware and FPGA software)– first full chain for one detector to be tested in spring 2006

• Tracking methods– full MC simulation of the system well advanced– pulse shape decomposition proceeding but still a kind of bottleneck– -ray tracking well advanced– simulation of experiments, including ancillary detectors, progressing

well

• Configuration chosen in 2004• Development of Demonstrator ready in

2007• Next phases discussed in 2005-2006• New MoU and bids for funds in 2006-2007• Start construction in 2008

– 1 ready in 2010 (10 M€) ~ 4 clusters/year

– 3 ready in 2015 (20 M€)– 4 ready in 2018 (10 M€)

Status and Evolution

Keeping the schedule depends on availability of fundsand production capability of detector manufacturer

Possible scenario(not yet officially

discussed)

5 Clusters5 ClustersDemonstratorDemonstrator

The Phases of AGATA

GSI FRS RISINGLNL PRISMA CLARAGANIL VAMOS EXOGAMJYFL RITU JUROGAM

12007

Main issue is Doppler correction capability coupling to beam and recoil tracking devicesImprove resolution at higher recoil velocity

Extend spectroscopy to more exotic nuclei

Peak efficiency3 – 8 % @ M = 1

2 – 4 % @ M = 30

Replace/Complement

15 Clusters 15 Clusters 11

The Phases of AGATA 2

The first “real” tracking arrayUsed at FAIR-HISPEC, SPIRAL2, SPES, HI-SIBCoupled to spectrometer, beam tracker, LCP arrays …Spectroscopy at the N=Z (100Sn), n-drip line nuclei, …

0

5

10

15

20

25

30

35

40

45

50

1 2

Effi

cie

ncy

(%

)

Solid Angle (%)

Efficiency M = 1

Efficiency M = 10

Efficiency M = 20

Efficiency M = 30

= 0 = 0.5

The Phases of AGATA 345 Clusters45 Clusters

33

Ideal instrument for FAIR / EURISOLAlso used as partial arrays in different labsHigher performance by coupling with ancillaries

60 Clusters60 Clusters44

The Phases of AGATA 4

Full ball, ideal to study extreme deformationsand the most exotic nuclear speciesMost of the time used as partial arraysMaximum performance by coupling to ancillaries

SummarySummary

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

• Work continues ...

PreamplifiersPreamplifiers

• Discrete hybrid solution developed in collaboration between Milano, Köln, GANIL

• Cold FETs• Differential output to the

digitizers• Fast reset to limit the

effects of signal saturation

• ASIC solution is being investigated (Saclay, Milano)

MC Simulation of ExperimentMC Simulation of Experiment

“perfect” position resolutionFWHM = 2.6 keV

interaction points with “simulated”<d> 5 mm errorFWHM = 3.5 keV

non-corrected spectrum

Simulated resolutions have to be folded with intrinsicenergy resolution of detector 2.2 keV @ 846.8 keV

Effects considered in the simulation:

Opening angle of PHOBOS 1.3

Target thickness

- dE/dx before and after scattering

-CLX as function of energy

Beam spot 2 mm

MARS: = 134.6=270.4d = 17

cm

PHOBOS: = 53.1=216.5

Beam: 56Fe 240 MeV

Target: 208Pb 3.7 mg/cm2

Average 7.4%

“simulated” error obtained from reconstruction of simulated interactions points using a GA

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/event

80 MB/s

~ 200 B/segment~ 2 MB/s

100 Ms/s

14 bits

Pulse Shape Analysis

Event Builder

-ray Tracking

HL-Trigger, Storage On 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 Electronics and DAQ for AGATAAGATA

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

GTS …detector

Preamps

Digitizers

detector

Preamps

Digitizers

Localprocessing

Localprocessing

7.4 GB/s/det

PSA PSA

1 MB/s/det

20 MB/s/det

Digital

Digital

preamplifier

preamplifier

On line…Storage …

Tracking

EventBuilder

< 200 MB/s

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

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

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

Trigger-less system. Global trigger possible.Global event builder and software trigger

On-line gamma-ray tracking

Control and storage (~1 TB/year), …

AGATA/GRETA Prototypes

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

Courtesy Canberra-Eurisys

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

GRETA vs. AGATA - II

A recoil half-opening angle of 10º and a

single 1 MeV photon is assumed

Which translates into a better peak-to-background (P/B) ratio:

Assuming the same position resolution within the crystals, in the case of AGATA a better quality of the spectra is obtained, given the better definition of the direction of the photons (implying a better Doppler correction). This is equivalent to an increase of resolving power R:

At =50% and fold F=10, P/B for AGATA is approximately 6 times P/B for GRETA

T

P

FWHM

SER

FRB

P