AGATA: Status and Perspectives

AGATA: Status and Perspectives AGATA: Status

and Perspectives

E.Farnea

INFN Sezione di Padova, Italy

on behalf of the AGATA Collaboration

Outline Outline

• 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 systemsEuropean -ray detection systems

TESSA ESS30

EUROGAM

GASP

EUROBALL III

EUROBALL IV 1980 1986 1992 1996

Composite & encapsulated detectorsComposite & encapsulated detectors

CLOVER

EB-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

48Ni

100Sn

78Ni

Proton drip line and N=Z nuclei

• Spectroscopy beyond the drip line

• Proton-neutron pairing

• Isospin symmetry

Transfermium nuclei Shape 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 efficiency High sensitivity High throughput

Ancillary detectors

FAIRSPIRAL2

SPESREX-ISOLDE MAFFEURISOL

HI-Stable

Harsh conditions!

Need instrumentation with

Conventional arrays will not suffice!

Efficiency vs. Resolution Efficiency 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 d

Large d Large 

Small  High 

Low  Poor FWHM

Good FWHM

Compton scattering Compton 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 trackingFrom conventional Ge to -ray tracking

ph ~ 10%

N_det ~ 100

Using only conventional Ge detectors, too many

detectors

are needed to avoid summing effects and keep

the resolution to good values

The proposed solution:

Use the detectors in a non-conventional way!

Compton Shielded Ge

Ge Sphere

Ge Tracking Array

ph ~ 50%

N_det ~ 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%

N_det ~ 100

 ~80%

AGATA and GRETA

Ingredients of Gamma Tracking

Pulse Shape Analysis to 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 electronics to record and process segment

signals

1

2

3

4

Reconstructed gamma-rays

Arrays of segmented Ge detectors

(for Doppler correction)

MINIBALL triple-clusters with 6 and 12 fold segmentation

Segmented Germanium Array (SeGA) with 32-fold segmentation

EXOGAM segmented clovers with 4x4 fold segmentation

Pulse Shape Calculations and Analysis by a Genetic Algorithm

Pulse Shape Calculations and Analysis by a Genetic Algorithm

net charge signals



transient signals













 





 





 

Base system of signals

measured or calculated

GA GA

Sets of interaction

points (E; x,y,z)_i

measured signals

signals reconstructed

from base



Reconstructed set of interaction points

(E; x,y,z)_i

„fittest“ set

Weighting field method:

Weighting field method:

Th. Kröll, NIM A 463 (2001) 227

In-beam test of PSA: MARS detectorIn-beam test of PSA: MARS detector

Corrected using points determined with a Genetic Algorithm

Corrected using center of crystal

 one detector with   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

β 1

βcos(θ) E 1

E 2

Lab γ CM

γ 

 

FWHM 16.5 keV FWHM 6.3 keV FWHM 4.5 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 searchAn 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

• The pulse shapes associated to one point in the base 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 event

E=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 germaniumInteraction 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 algorithms Tracking algorithms

Basic ingredient:

Compton scattering formula

 

 



















 











 







 

 







1 n P 2

E

P 2

0 E

E P

' P

1 1 E

' E 1

2 2 E

2 E

cosθ c 1

m 1 E

E E 12

01

12 cosθ 01

E E

γ' γ'

n n

e e

N n i

i N

n i

i

















Reconstruction of multi-gamma eventsReconstruction 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, E_0 =  cluster depositions

2. Test the 3 mechanisms

1. do the interaction points satisfy the Compton scattering rules ?

2. does the interaction satisfy photoelectric conditions

(e₁,depth,distance to other points) ? 3. do the interaction points correspond

to a pair production event ? E_1st = E_ – 2 m_ec²

3. Select clusters based on ²

 ^

 









 

1 

N 1

n γ n

Pos γ'

n

2 E

E E 2 W



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 around

100-250 keV

83% 87%

=> interaction points within a given deposited

energy interval (e_min < e_i < e_max) will be considered as the last interaction of a fully absorbed gamma

Backtracking

B. 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: e_min< e_i < e_max

prob. for photoelectric interaction > P_phot,min distance between interaction points < limit

cos(energy) - cos(position) < limit prob. for Compton interaction > P_comp,min

distance between interaction points < limit cos = 1 – m_ec²(1/E_sc –1/E_inc)

E_inc = e_i + e_j, E_sc = e_i

E_inc = e_i+e_j+e_k E_sc = e_i+e_j

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 trackingBenefits of the -ray tracking

scarce

good

Definition of the photon direction Doppler correction capability

Detector

Segment

Pulse shape analysis

+

tracking 

Energy (keV)

v/c = 20 %

AGATA AGATA

• 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 a platonic solid

e.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 the spherical tiling generates the shapes of the detectors.

Ball with 180 hexagons.

Space for encapsulation and canning obtained cutting the crystals. 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 spacing

0.8 mm thick Al canning 2 mm spacing

2 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

*Agata RunAction

*Agata EventAction

Agata PhysicsList

Agata VisManager

Agata

SteppingAction

*Agata

Analysis Agata

GeneratorAction

CSpec1D

Agata

GeneratorOmega

Agata

SteppingOmega

*Agata Detector Construction

*Agata Detector

Shell

*Agata Detector

Simple

*Agata

SensitiveDetector

*Agata

DetectorArray

Agata HitDetector CConvex

Polyhedron

Messenger classes are not shown!

Messenger classes are not shown!

* Possibility to change parameters via a messenger class

*Agata

DetectorAncillary

CSpec2D

*Agata

Emitted

Agata

Emitter

*Agata

ExternalEmission

*Agata

ExternalEmitter

*Agata

InternalEmission

*Agata

InternalEmitter

GRETA vs. AGATA

120 hexagonal crystals 2 shapes 30 quadruple-clusters all equal Inner radius (Ge) 18.5 cm Amount of germanium 237 kg Solid 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 shapes 60 triple-clusters all equal Inner radius (Ge) 23.5 cm Amount of germanium 362 kg Solid angle coverage 82 % 6480 segments

Efficiency: 43% (M_=1) 28% (M_=30) Peak/Total: 58% (M_=1) 49% (M_=30)

Expected Performance Expected Performance

Response 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 cryostat used for acceptance tests

“standard” preamplifiers

Encapsulation

0.8 mm Al walls 0.4 mm spacing

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

Segmentation of AGATA crystals

The impact of effective segmentation

r [cm]

z [cm]

geometrical segmentation

tapering angle ~ 8°

Guaranteed FWHM

at 1.33 MeV : < 2.30 keV, mean < 2.1 keV at 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 keV at 122 keV : 1.35 keV Measured FWHM

at 1.33 MeV : 2.13 keV at 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 experiments

differential-output preamplifiers with fast reset of saturated signals (Milano/Ganil, Köln)

AGATA detector scanning

Liverpool coincidence setup with multileaf collimator

Other system being developed at 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 allow

Operation of Ge detectors in position sensitive mode  -ray tracking

Demonstrator ready by 2007; Construction of full array from 2008

AGATA AGATA

(Advanced GAmma Tracking Array)

4 -array for Nuclear Physics Experiments at European accelerators

providing radioactive and high-intensity stable beams

Chairperson J.Gerl, Vice Chairperson, N.Alamanos G.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 Groups

Detector Module J.Eberth

Detector Performance

R.Krücken

Data Processing D.Bazzacco

Design and Infrastructure

G.Duchêne

Ancillary detectors and Integration

A.Gadea

Simulation and Data Analysis

J.Nyberg

Preamplifiers A.Pullia Detector and

Cryostat D.Weisshaar

PSA R.Gernhäuser/

P.Desesquelles Detector Characterisation

A.Boston

Digitisation P.Medina Pre-processing

I.Lazarus Global clock

and Trigger M.Bellato Data acquisition

X.Grave Run Control

& GUI G.Maron

Mechanical design K.Fayz/J.Simpson

Infrastructure P.Jones R&D on gamma

detectors D.Curien

Electr. and data acq.

Ch. Theisen Impact on performance

M.Palacz

Mechanical integration Devices for key

Experiments N.Redon

Gamma-ray Tracking W.Lopez-Martens Experiment simulation

E.Farnea Detector data base

K.Hauschild Data analysis

O.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-cluster 5 asymmetric triple-clusters

36-fold segmented crystals 540 segments

555 digital-channels Eff. 3 – 8 % @ M_ = 1 Eff. 2 – 4 % @ M_ = 30 Full ACQ

with on line PSA and -ray tracking Test Sites:

GANIL, GSI, Jyväskylä, Köln, LNL Cost ~ 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 funds and production capability of detector manufacturer

Possible scenario (not yet officially

discussed)

5 Clusters 5 Clusters Demonstrator Demonstrator

The Phases of AGATA

GSI FRS RISING

LNL PRISMA CLARA

GANIL VAMOS EXOGAM

JYFL RITU JUROGAM

1

2007

Main issue is Doppler correction capability

 coupling to beam and recoil tracking devices

Improve resolution at higher recoil velocity Extend spectroscopy to more exotic nuclei

Peak efficiency 3 – 8 % @ M_ = 1 2 – 4 % @ M_ = 30

Replace/Complement

15 Clusters 15 Clusters

11

The Phases of AGATA 2

The first “real” tracking array

Used at FAIR-HISPEC, SPIRAL2, SPES, HI-SIB Coupled 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

Efficiency (%)

Solid Angle (%) Efficiency M = 1 Efficiency M = 10 Efficiency M = 20 Efficiency M = 30

 = 0  = 0.5

The Phases of AGATA 3

45 Clusters 45 Clusters

33

Ideal instrument for FAIR / EURISOL

Also used as partial arrays in different labs

Higher performance by coupling with ancillaries

60 Clusters 60 Clusters

44

The Phases of AGATA 4

Full ball, ideal to study extreme deformations and the most exotic nuclear species

Most of the time used as partial arrays

Maximum performance by coupling to ancillaries

Summary Summary

• Gamma-ray tracking arrays will be very powerful tools to extract

valuable information for nuclear structure and reaction studies

• Work continues ...

Preamplifiers Preamplifiers

• 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 resolution FWHM = 2.6 keV

interaction points with “simulated”

<d>  5 mm error FWHM = 3.5 keV

non-corrected spectrum

Simulated resolutions have to be folded with intrinsic energy 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=270.4d = 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 of pulse 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 AGATA Electronics and DAQ for AGATA

Fully synchronous system with global 100 MHz clock and time-stamp

distribution (GTS) GTS ^detector …

Preamps

Digitizers

detector Preamps

Digitizers

Local

processing Local processing

7.4 GB/s/det

PSA PSA

1 MB/s/det 20 MB/s/det

Digital Digital

preamplifier preamplifier

On line…

Storage … Tracking

Event Builder

< 200 MB/s

Local processing triggered by Ge common contact. Determine energy and isolate

~ 600 ns of signal around rise-time Digitizers: 100 Ms/s, 14 bit

Optical fiber read-out of full data stream to pre-processing electronics

Buffers of time-stamped local events sent to 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 shape Taper angle 10º

Diameter (back) 80 mm

Length 90 mm

Weight 1.5 kg

Outer 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 R  SE^

RF

BP 