advanced gamma – ray spectroscopy with agata

Advanced Gamma–Ray Spectroscopy

Techniques with the AGATA Segmented

DetectorsCălin A. Ur*

for the AGATA CollaborationINFN – Sezione di Padova

*On leave from IFIN–HH Bucharest

Layout

01/02/2010 2ELI NP Workshop Bucharest

• Principles of the AGATA gamma–ray tracking array

• Building phases of the array• The AGATA Demonstrator• First tests at the National Laboratories

of Legnaro• Compton imaging with segmented

detectors

Extreme Experimental Conditions


• Low intensity• High backgrounds• Large Doppler

broadening• High counting rates• High -ray multiplicities

High efficiencyHigh sensitivityHigh throughputAncillary detectors

FAIRSPIRAL2SPESREX-ISOLDEEURISOLHI-SIB

Need instrumentation

Extreme Experimental Conditions


• Low intensity• High backgrounds• Large Doppler

broadening• High counting rates• High -ray multiplicities

High efficiencyHigh sensitivityHigh throughputAncillary detectors

FAIRSPIRAL2SPESREX-ISOLDEEURISOLHI-SIBELI ?

Need instrumentation

The New Concept of Tracking Arrays


Tracking Arrays based onPosition Sensitive Ge Detectors

Gamma Arrays based on Compton Suppressed Spectrometers

~ 50 — 25 % ( M=1 — M=30)

~ 10 — 7 % ( M=1 — M=30)

GAMMASPHEREEUROBALL GRETAAGATA

AC

AC

Comptonrejected

Full energyaccepted

Analogue vs Digital Electronics


Detector(Germaniu

m)

Shaping Amplifier

CFD DAQ

E

t

FADC

MWD

NSR

Filters

DAQ

E

t

ADC

TDC

PSA

Trac

king

E

t

x,y,z

E

t

Present Arrays

AGATA

Segment Detector Array

Detector(Germaniu

m)

Ingredients of Gamma–Ray Tracking


Pulse Shape Analysisto decompose

recorded waves

Highly segmented

HPGe detectors

··

Reconstruction of tracks evaluating permutations

of interaction points

Digital electronicsto record and

process segment signals

1

23

4

Reconstructed

gamma-rays

Th. Kröll, NIM A 463 (2001) 227

Position Determination – PSA


FEM-modelof detector

Calculateweighting

fields

Calculation of the signals induced on the contacts using the weighting field method

transient signals

net charge signals

Pulse Shape Analysis Concept


B4 B5B3

C4 C5C3

CORE

A4 A5A3

C4

D4

E4 F4

A4

B4

x

y

z = 46 mm

791 keV deposited in segment B4

(10,10,46)

measured

(10,30,46)



B4 B5B3

C4 C5C3

CORE

A4 A5A3

C4

D4

E4 F4

A4

B4

x

y

z = 46 mm


(10,10,46)

measuredcalculated



B4 B5B3

C4 C5C3

CORE

A4 A5A3

C4

D4

E4 F4

A4

B4

x

y

z = 46 mm


(10,15,46)

measuredcalculated



B4 B5B3

C4 C5C3

CORE

A4 A5A3

C4

D4

E4 F4

A4

B4

x

y

z = 46 mm


(10,20,46)

measuredcalculated



B4 B5B3

C4 C5C3

CORE

A4 A5A3

C4

D4

E4 F4

A4

B4

x

y

z = 46 mm


(10,25,46)

measuredcalculated



B4 B5B3

C4 C5C3

CORE

A4 A5A3

C4

D4

E4 F4

A4

B4

x

y

z = 46 mm


(10,30,46)

measuredcalculated



Result of Grid Search

algorithmR. VenturelliB4 B5B3

C4 C5C3

CORE

A4 A5A3

C4

D4

E4 F4

A4

B4

x

y

z = 46 mm


(10,25,46)

measuredcalculated

Interaction/Reconstruction Algorithms


~ 100 keV ~1 MeV ~ 10 MeV -ray energy Photoelectric Compton Scattering Pair Production

Algorithms: ClusterTracking, FuzzyTracking, BackTracking, …Reconstruction efficiency limited by Position resolution and Compton profile.

Probability ofinteraction depth

Isolated hits

cosθ1cm

E1

EE

20

γ

γγ'

Angle/Energy

Pattern of hitsE1st = E – 2 mc2



Idealized configuration to determinemaximum attainable performance.

Ri = 15 cmRo = 24 cm230 kg of Ge

Events simulated using GEANT4Response of shell at 1.33 MeV:ph = 70% P/T = 77%Reconstruction by Cluster-TrackingPacking Distance: 5 mmPosition Resolution: 5 mm (at 100 keV)1.33 MeV

M = 1

M = 30

ph (%) 65 36P/T(%) 85 60

27 gammas detected -- 23 in photopeak16 reconstructed -- 14 in photopeak

E = 1.33 MeVM = 30

A high multiplicity event

D. Bazzacco

Possible Array Configurations


120 crystals

180 crystals

Configuration A120 A120F A120C4 A180

Crystals (shapes) 120 (2) 120 (6) 120 (2) 180 (3)

Clusters (shapes) 40 (2) 40 (2) 30 (1) 60 (2)Ge solid angle (%) 71.0 77.8 78.0 81.6Ge weight (kg) 232 225 230 363Centre to Ge (cm) 19.7 18 18.5 23.5Electronics channels 4440 4440 4440 6660

Eff. at M = 1 (%) 32.9 36.9 36.4 43.3Eff. at M = 30 (%) 20.5 22.0 22.1 28.1P/T at M = 1 (%) 52.9 53.0 51.8 58.2P/T at M = 30 (%) 44.9 43.7 43.4 49.1

A180 is AGATA’s choice

GRETA is for A120C4

The Advanced GAmma Tracking Array


Requirementsefficiency, energy resolution, dynamic range, angular resolution, timing, counting rate, modularity, angular

coverage, inner space

Quantity Specified for Target Value

Photo-peak efficiency (ph)

Eγ = 1 MeV, Mγ = 1, < 0.5Eγ = 1 MeV, Mγ = 30, < 0.5Eγ = 10 MeV, Mγ = 1

50 %25 %10 %

Peak-to-total ratio (P/T)Eγ = 1 MeV, Mγ = 1Eγ = 1 MeV, Mγ = 30

60 - 70 %40 - 50 %

Angular resolution () E/E < 1% better than 1

Maximum event ratesMγ = 1Mγ = 30

3 MHz300 kHz

Inner space for ancillaries > 170 mm

Construction of the AGATA Array


Total weight of the 60 clusters of the AGATA-180 configuration ~2.5 tonsMounted on a self-supporting structure

Ge crystals:Hexaconical shape90-100 mm long80 mm max diameter36 segmentsAl encapsulation: 0.4 mm spacing 0.8 mm thickness

Distance between faces of crystals: in same cluster ~2.5 mm in adjacent clusters ~9.0 mm

Triple clusters: 3 encapsulated crystalsAl end-cap: 2.0 mm spacing 1.0 mm thickness111 cold FET preamplifiers

Asymmetric AGATA Triple Cryostat


Challenges: - mechanical precision - heat development, LN2 consumption - microphonics - noise, high frequencies

- integration of 111 high resolution spectroscopy channels- cold FET technology for all signals

@1.3 MeV@ 60 keV

Core2.10 keV @ 1.3 MeV1.20 keV @ 60 keV

Electronics and DAQ

22

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

5 MB/s/det

100 MB/s/det

DigitalDigital

preamplifier

preamplifier

On line…Storage …

Tracking

EventBuilder

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 to extract position of interactionsTrigger-less system. Global trigger possible.

Global event builder and software trigger

On-line gamma-ray tracking

Control and storage (~1 TB/year), …

clk

@ 50 kHz

01/02/2010 ELI NP Workshop Bucharest

The Phases of AGATA 1


5 Clusters5 ClustersDemonstratDemonstrat

oror

Our days

Main issue is Doppler correction capability coupling to beam and recoil tracking devices Improve resolution at higher recoil

velocityExtend spectroscopy to more exotic nuclei

Peak efficiency3 – 8 % @ M = 12 – 4 % @ M = 30



The first “real” tracking array

To be used at FAIR-HISPEC, SPIRAL2, SPES, …

15 Clusters 15 Clusters 11

0

5

10

15

20

25

30

35

40

45

50

1 2

Effi

cien

cy (%

)

Solid Angle (%)

Efficiency M = 1

Efficiency M = 10

Efficiency M = 20

Efficiency M = 30

= 0 = 0.5

Near future

Recoil velocity



Efficient as a 120 ball (20% at high multiplicity)

Ideal for FAIR and EURISOL

45 Clusters45 Clusters33

Far future



Full ball / full performance

Ideal to study extreme deformations and the most exotic nuclear species

60 Clusters60 Clusters44

Remote future

The AGATA Demonstrator


Objective of the R&D phase 2003-2008

5 asymmetric triple-clusters36-fold segmented crystals540 segments555 digital-channelsEff. 3 – 7 % @ M = 1Eff. 2 – 4 % @ M = 30

Full ACQ online PSA and –ray trackingCost ~5 M€

Present status3 asymmetric triple-clusters mounted&tested at INFN LN Legnaro +1 in deliveryUndergoing commissioning runs detectors, DAQ, PSA, onlinePhysics campaign to start in ~1 month

First in–beam Test at LNL


• Week 12 (March 16-22) • 30Si(@70MeV)+12C fus.–evap. reaction in inverse kinematics

• The system included– full AGATA DAQ chain– PSA and tracking performed in real time (online)

• Goal – test the whole system under real data taking conditions– test Doppler correction capability of the AGATA detectors

Doppler Broadening and Position Res.


Position resolution

Angular resolution

Energy resolution

BeamRecoil

ray

Doppler Broadening and Position Res.


12.5 keV40K1823

keV ~ 5%

full detectorsegments (17.7 keV)PSA+tracking

Full optimization and analysis – 1 month

onlineour target

Compton Imaging


• In-beam experiment– given the position

of the target we track the rays

• Compton imagingof a radioactive source– inverse tracking –

from the first 2 interaction points get the position of the source

E1 E2

target

E1 E2

-source

Compton scattering – a tool for testing the position resolution

ray

ray

Compton scattering

F. Recchia

Principles of Compton Imaging


[d

eg]

20

111cos cmEE

Compton Imaging Performance


Sources of error in the identification

of the source direction:

• Position resolution (axis)• Energy resolution (scattering

angle)• Compton profile (scattering

angle)

scattering angle [deg]

angu

lar e

rror [

deg]

Experimental Setup at LNL


Digital DAQ system provided by IFIN – HH Bucharest

• 10 x TNT2 NIM Digitizer boards from CAEN with 4ch 14bit /100MHz

AGATA prototype detector(one symmetric capsule)

60Co source

Comparison with MC Simulations


profile of experimental imageMonte Carlo +

5 mm position resolution

profile of experimental image

5.2

4.7

Experiment

[d

eg]

[deg]

[d

eg]

peak

FW

HM[

deg]

peak

FW

HM[

deg]

position resolution FWHM[mm]

position resolution FWHM[mm]

After PSAProjections

MC

MC

Gamma Background Rejection


characterize the capability of the AGATA detectors to discriminate different gamma source locations using Compton imaging algorithmExperimental Setup: 3 –ray sources 60Co, 152Eu and 137Cs

their positions simulate the beam-dump, the beam line and the target

M. Doncel & F. Recchia

Results


b)

a)

c)

Spectra of the gamma radiationassigned to each source positionwith the algorithm

Spectra assignment a) corresponds to the 60Co position b) corresponds to the 137Cs position c) corresponds to the 152Eu position

•promising results•need more refinement of the method E = 344 keV

E = 661 keV

E1 = 1173 keVE2 = 1332 keV

Outlook


To exploit the present and future facilities fully and most efficiently, advanced instrumentation and detection equipment is required – NuPECC recommendationThe 4-array of highly segmented Ge detectors AGATA for -ray detection and tracking is part of this effortFirst measurements in-beam and with sources show that the position resolution is ~ 5 mm FWHM; this value is in line with the design assumptions of the AGATA spectrometer, confirming the feasibility of -ray trackingAGATA will have a strong impact on nuclear structure studies : lifetime measurements of nuclear states down to fs, angular distribution and polarization measurements Is AGATA or part of it of interest for the ELI project?

The AGATA Collaboration


Bulgaria: SofiaDenmark: CopenhagenFinland: JyväskyläFrance: GANIL, Lyon, Orsay, Saclay, StrasbourgGermany: Berlin, Bonn, GSI, Darmstadt, Jülich, Köln,

MünchenHungary: DebrecenItaly: Padova, Milano, LNL, Firenze, Camerino, Napoli,

GenovaPoland: Krakow, Swierk, WarsawRomania: BucharestSweden: Lund, Stockholm, UppsalaTurkey: Ankara, IstanbulUK: Daresbury, Brighton, Keele, Liverpool,

Manchester, Paisley, Surrey, York

Outlook


First in–beam test with STC


32 keV

11 keV

4.8 keV4.8 keV

Symmetric triple cluster

Silicon detector

experiment performed at IKP of Cologne

Position resolution extracted through a comparison to detailed Monte Carlo simulations (FWHM vs. pos. resolution)

~5.2 mm

New Challenges from the RIB Facilities


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

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

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

Nuclear Astrophysics• Properties of r and rp process nuclei

advanced gamma – ray spectroscopy with agata

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