GRETINA - CNEAscoccola/iguazu/Pt/09_PT09... · 2005-10-28 · Summary γ1 Large arrays of Ge...

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SLAFNAP6 IGUAZU - ARGENTINA October 3-7, 2005 A. O. Macchiavelli Lawrence Berkeley National Laboratory GRETINA Many Thanks to I-Yang Lee, P.Fallon, M.Descovich and S.Ettenauer

Transcript of GRETINA - CNEAscoccola/iguazu/Pt/09_PT09... · 2005-10-28 · Summary γ1 Large arrays of Ge...

Page 1: GRETINA - CNEAscoccola/iguazu/Pt/09_PT09... · 2005-10-28 · Summary γ1 Large arrays of Ge detectors such as Gammasphere and Euroball had a large impact in nuclear structure research

SLAFNAP6IGUAZU - ARGENTINA

October 3-7, 2005

A. O. MacchiavelliLawrence Berkeley National Laboratory

GRETINA

Many Thanks toI-Yang Lee, P.Fallon, M.Descovich and S.Ettenauer

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Outline

Introduction

Concept of γ-ray tracking

Impact on spectroscopy

Proof of principleSegmented detectorsElectronicsPosition reconstructionIn-beam results

GRETINADesign and expected performanceStatus of the project

Summary and conclusions

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Gamma-ray spectroscopy has played a major role in the study of the atomic nucleus.

Development of new detectors and techniques have always led to discoveries of new and unexpected phenomena.

Gamma-ray Spectroscopy and Nuclear Physics

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“Spectroscopic history”of 156Dy

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Resolving power - Figure of Merit

“Effective” Energy resolution (δE), Efficiency (ε), Peak-to-total (P/T)

Plus auxiliary devices

Weakest branch that can be resolved

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fold

α(lo

g)

1/rf

(N/No)/εf

Resolving power - Figure of Merit

f*

Resolving powerα*

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Evolution over the years

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- HV signal

p n

Intrinsic energy resolution determined by statistics of charge carriers ~

valence band

conduction band

0.7 eV ε=3 eV

Germanium Semi-conductor Detectors

Best energy resolution

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Moving nucleus

θ

γ-ray detector

V±ΔVΔθΝ

ΔθD

Broadening of detected gamma ray energy due to:Spread in speed ΔVDistribution in the direction of velocity ΔθΝDetector opening angle ΔθD

Need accurate determination of V and θ.Position sensitive γ-ray detector and particle detector

Doppler shift

Doppler Broadening

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Doppler Broadening

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Peak/Total = 20%ε=20%

Compton suppressor

20%

Veto

P/T=60%ε =20%

Compton Suppression

Improve peak-to-total ratio

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Number of modules 110Ge Size 7cm (D) × 7.5cm (L)Distance to Ge 25 cm

Peak efficiency 9% (1.33 MeV)Peak/Total 55% (1.33 MeV)Resolving power 10,000

Almost 10 !Almost 10 !

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Ν = 100ΝΩ ε = 0.1Efficiency limited

Veto

Compton Suppressed Ge Ge Sphere Gamma Ray Tracking

Ν = 1000 (summing)ΝΩ ε = 0.6Too many detectors

Ν = 100ΝΩ ε = 0.6Segmentation

sum

Towards the “Ultimate” Ge Array

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Pulse shape analysis in segments3D position of interaction points

Tracking of photon interaction points energy and position of γ-ray

Gamma-ray Tracking

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• High position resolution

• High efficiency

• High peak to background• High counting rate• Background rejection

Large recoil velocity– Fragmentation and– Inverse reactions

Low beam intensity

High background rate– Beam decay– Beam impurity

Advantages of γ-ray Tracking(In particular for Radioactive Beams)

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Resolving power: 107 vs. 104

– Cross sections down to ~1 nb• Most exotic nuclei• Heavy elements (e.g. 253,254No)• Drip-line physics• High level densities (e.g. chaos)

Efficiency (high energy) (23% vs. 0.5% at Eγ=15 MeV)

– Shape of GDR– Studies of hypernuclei

Efficiency (slow beams) (50% vs. 8% at Eγ =1.3 MeV)

– Fusion evaporation reactionsEfficiency (fast beams) (50% vs. 0.5% at Eγ =1.3 MeV)

– Fast-beam spectroscopy with low rates -> RIA

Angular resolution (0.2º vs. 8º)– N-rich exotic beams

• Coulomb excitation– Fragmentation-beam spectroscopy

• Halos• Evolution of shell structure• Transfer reactions

Count rate per crystal (100 kHz vs. 10 kHz)

– More efficient use of available beam intensity

Linear polarization

Background rejection by direction

Physics opportunities with a 4π array GRETA

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Signal Generation

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Dx

Q (%)

x=0

x=D/2

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V=1V=0

V=0

Ex weighting field

weighting potential

AB

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Q (%) time

A

B

A+B

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Advances in detector segmentation

Electronics developmentLow noise high bandwidth preamplifier

Rapid sampling, high resolution pulse digitizer

Signal analysis algorithm

Tracking algorithm

Computing power for on-line processing

Technical Challenges

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SeGA MSUANL - GARBO EXOGAM

Segmented Germanium Detectors

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MINIBALL AGATATIGRESS

Segmented Germanium Detectors

GRAPE

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Prototype detectors at LBNL

PII

PIII

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Segments and segment size

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Pre-Amp

Eurisys PSC823

FET IF1320

Gain 200mV/MeV

Rise Time ~40nsec

Decay Time 50μsec

Power 50mW

Performance with detector: Energy resolution 1.15 keV Am

2.5 keV Co

Noise level 4 keV (20MHz)

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LBNL VME 8-channel digital signal processing boards (100 MHz- 12 bit) Individual or Common clockProgrammable triggerFPGA Energy (P/Z)FPGA CFD timingUp to 10μsec data samples

Digitizer and Data Acquisition

Acquisition rate > 8 Mbytes/secData stored to a redundant disk array (1Tbytes) over Gigabit networkSuite of offline analysis programs

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Detector characterization

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At the hospital

UC Berkeley Medical Center

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Singles Scan

Am source scans to determine position of segment boundaries.

X

Y114μCi Am source (60keV)

Vertical and horizontal collimators (2mm) to define x,y and z

Automatic scan on pre-determined x,y,z pattern.

1min per point

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0

200

400

600

800

1000

1200

1400

0 10 20 30 40 50 60 70

Y (mm)

Cou

nts

60ke

V A

m

Singles Scan

Deviation from nominal values

dX =0.1+/-0.1 mm

dY =0.2+/-0.1mm

dα = 0 +/- 1 deg

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ε3

central

Energy central contact

Crystal Orientation

Gate on Am

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Coincidence Scans

Pulse shape measurement using a prompt coincidence requirement between GRETINA and Clover(s)

1mCi 137Cs source

Vertical and slit collimators to define 90 deg scattering

500nsec overlap

Coincidence trigger ~ 200 events/day

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Coincidence Scans

A

Clover 2 crystals

369-379 keV

Eclover+EA= 662keV

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Pulse Shapes

12

34

5

6

Δx =5mm

~ 200 events

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Pulse Shapes

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Tracking

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First step – cluster finding

Any two points with θ < θp are groupedinto the same cluster

Tracking

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Second step – Tracking of Compton scattering interaction points

Problem: 3!=6 possible sequences Assume: Eγ = Ee1 + E e2 + Ee3 ;γ-ray from the source

Sequence with the minimum χ2 < χ2 max

correct scattering sequencerejects Compton and wrong direction

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Ideal Shell

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Let’s put it all together

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Full analysis of simulated and experimental data

GEANT Signal calculation

Signalanalysis Tracking

Signaldigitizer

XYZE

XYZE

γ-ray

γ-ray

• Detector geometry

• Drift velocity• Electronics response

signals

signals

Spectra →Efficiency, P/T

Imaging

Field calculation

Electric field

Austin Kuhn, PhD Thesis, UC Berkeley, 2002.

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• Eγ=0.662 MeV (137Cs), source distance= 12cm

• Signal analysis (least square method)• up to 4 segments and 2 interactions per

segment (98% of all events)

• For single interaction per segment• position determination <1.5 mmsuccess rate ~80%

• For two interactions per segment• position determination < 1.5 mm

success rate ~70%• minimum separation 2 mm

• Compared data and simulation with and without tracking

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137Cs source

Simulation

Data

P/T ~ 38%

Relative Eff ~ 0.67

P/T ~ 31%

Relative Eff ~ 0.62

Tracking

P/T no tracking ~ 16%

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“Battle” conditions

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• 82Se + 12C @ 385 MeV• 90Zr nuclei (β ~ 8.9%)• 2055 keV (10+ 8+) in 90Zr• Target-detector @ 4 cm• Beam-detector @ 900

Experimental measurement of position resolutionDoppler broadening related to ΔrMaximize Doppler effect

In-beam Test of PII and PIII

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θβ

γγ cos11 2

0

−−

= EEDoppler shift:

θ

γ-rayinteraction

position

Beam

Target

Digitized pulse shapes have been analyzed to extract energy and position of individual γ-ray interactions (signal decomposition ).

The position of the 1st

interaction was used to correct for Doppler shift.

Data Analysis

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Comparison between the observed signals and a linearcontribution of pre-calculated basis signals:

Q(t)=Eiqi(t)+Ej qj(t)+…

Basis signalDetector signal

Signal DecompositionNew codeDavid Radford - ORNL

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From simulations, 14.5 keV FWHM

σ = 2.4 mm (RMS in 3D)correct for segment contact

correct for 1st interaction

FWHM28.3 keV

FWHM14.8 keV

Results

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Single segment

correct for central contact

correct for segment contact

correct for the first interaction

FWHM18 keV

FWHM28 keV

FWHM14 keV

Two segment

Results from PIII

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GG R E T I N A = 1/4 of 4π “First stage of GRETA”

But not But not ““Little GRETALittle GRETA””

GGamma Ray Energy Tracking In beam Nuclear Array

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Number of hexagons

Number of different hexagonal shapes

80 2 (20, 60)

110 3 (20, 30, 60)

120 2 (60, 60)

150 3 (30, 60, 60)

180 3 (60, 60, 60)

200 4 (20, 60, 60, 60)

12 pentagons and …

Geodesic tiling of the sphere

GS

AGATA

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4π Simulations GEANT4

Quad

Triplet

E.Farnea and D.Bazzacco - Padova

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- 7 quad modules + 1 triplet (31 crystals)- Cost of $17M- Construction period from 2005 – 2010

GRETINA

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Aux. Det. Trigger

Global TriggerModule

SignalDigitizers

Local TriggerModule

30 Crystals

Data Storage

2.2 MB/s

Aux. Det. Data

66 MB/s

75 dual Processors

Workstations, Servers

6.9 MB/s

2.3 MB/s + Aux. Data

NetworkSwitch

Processing Farm

ReadoutComputer

Data Acquisition System

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How does nuclear shell structure and collectivity evolve in exotic neutron-rich nuclei?

What is the influence of increasing charge on the dynamics and structure of the heaviest nuclei?

How do the collective degrees of freedom and shell structure evolve with excitation energy and angular momentum?

What are the characteristics of Giant Resonancesbuilt on excited states and loosely bound nuclei?

GRETINA Physics

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0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1 2 3 4 5 6 7 8

GS (lo)GS (hi)SeGA (lo)SeGA (hi)gretina (lo)gretina (hi)

Performance

Relative to a 4π arraysolid angle ~ 0.8, position resolution ~ 2mm

Low (lo) and high (hi) beam intensity

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n-rich nuclei from fragmentation reactions

Gamma-ray energy (2keV/channel)

30Na from 32Al Beam

30Na from 30Mg Beam

340

370410250

175

190

150

140

340

370410

250

175

770430 (3+--2+)

Simulation SeGA Simulation GRETINA

30Mg (pn) → 30Na (100 MeV/u)v/c=0.43

charge exchange reactionGamma-gamma coincidence

NSCL data SeGA(E. Rodriguez-Vieitez et al.)

Performance 1π

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High spin states from fusion reactions

Simulation GRETA, ε =0.25

4-fold, I=10-5

Simulation GS

Simulation GS, ε =0.09

3-fold, I=10-4

v/c=0.04

3-fold, I=10-3

64Ni ( 48Ca, 4n) 108Cd, Gammasphere

Performance 4π

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DOE - Critical DecisionsCD0 : Mission need Aug. 2003

CD1 : Preliminary Baseline Range Feb. 2004

CD2A/CD3A : Performance Baseline range for long lead time items June 2005

• CD2B/CD3B : Start Construction Sept. 2007

• CD4 : Start of Operation May 2010

Schedule

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• Argonne National Laboratory– Trigger system– Slow control software

• Michigan State University– Detector testing

• Oak Ridge National Laboratory– Liquid nitrogen supply system– Data acquisition

• Washington University– Target chamber

Collaborating Institutions

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Physics M. A. RileyDetector A. O. MacchiavelliElectronics D. C. RadfordSoftware M. CromazAuxiliary Detectors D. G. Sarantites

Working Groups

http://grfs1.lbl.gov/

http://radware.phy.ornl.gov/greta/join.html

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Summary

γ1 Large arrays of Ge detectors such as Gammasphere and Euroball had a large impact in nuclear structure research in the last decade.

γ2 A 4π Gamma-Ray Tracking Array appears as the next frontier and was identified as a new initiative by the nuclear structure communities in Europe and USA

γ3 GRETINA has just received CD2/3A approval from DOE.

γ4 With the AGATA demonstrator, first realization of a tracking device and offers a very compelling physics case

γ5 We look forward to an exciting research program.

Important applications in many fields

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Kai Vetter -LLNL

High energy astrophysicsCorrelate the detected photon to the source object as known from more precise observations in other wavelengths

Biomedical researchPrecise localization of radioactive tracers in the bodyCancer diagnosisMolecular targeted radiation therapyMonitor changes in the tracer distribution -> dynamical studies

National securityNuclear non-proliferation/ nuclear counter terrorismContraband detectionStockpile stewardshipNuclear waste monitoring and management

Industrial non-destructive assessmentsDetermination of the material density distribution between the source and detector

Why imaging gamma-rays?

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( )1

2011cos

EEEcmE−

−=γγ

θThe Compton scattering formula gives θ:

4321 EEEEE +++=γ

r1

r2r3

r4

θ

1E

γE

12rr

sourcesourceGamma rays interact several times with detector via Compton interaction (e.g. until it is stopped by the photo-electrical effect)

Measuring positions and energies of individual interactions enables to determine pathway of gamma ray in detector (tracking)

Energies and positions of first two interactions define cone of incident angles (electron path is not measured)

Cones are projected on plane or sphere (one circle per event) for 2D or into cube (one cone per event) for 3D imaging

source

Compton gamma-ray imaging

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4π photocamera4π photocamera

K.Vetter et al.

4π gamma-ray imaging

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Finally, to conclude, a word about the future …

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“The future isn’t what it used to be.”

Arthur C. Clarke

“Prediction is very difficult, especially about the future.”

Niels Bohr

Shrinking budgets

Limited resourcesNeed to find new opportunities

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However, with

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Electric field

ionconcentratimpurityVVE

:2 ρρ=∇

∇=rr

Boundary condition : applied bias voltage

Weighting potential for segment k

02 =∇ kVBoundary condition : 1 V on the segment k

0 V on all other segments

Signal Generation

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Trajectory : for electrons and holes

∫+=

=t

dtvxtx

Evv

00)(

)(rrr

vrv

Induced charge (S. Ramo, Proc. IRE 27(1939)584)

If a charge q moves from position x1 to position x2, then the induced charge on electrode k is

( ))()( 12 xVxVqQ kkkrr

−=Δ

anisotropic

Signal Generation

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Measurements using the digitizer board

Energy Resolution

Crystal A

0

0.5

1

1.5

2

2.5

3

3.5

0 6 12 18 24 30 36segment #

FWH

M (k

eV)

Am 60keV60Co 1173keV60Co 1332keV

2.55 keV

1.28 keV

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Segment number

σ (keV)

3.5 keV

Noise level at high-frequency

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Calculate signal in each segment for interactions on a grid

base signals

Decompose the composite signal into alinear combination of base signals

Interpolate to improve position resolution

Signal decomposition

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Results

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152Eu full analysisGain in peak/total vs. efficiency

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Neutron damage

Page 83: GRETINA - CNEAscoccola/iguazu/Pt/09_PT09... · 2005-10-28 · Summary γ1 Large arrays of Ge detectors such as Gammasphere and Euroball had a large impact in nuclear structure research

Fast neutrons damage the Ge structure and create hole-traps.Reduction of charge collection efficiency.Signal loss depends on the interaction position.Hole-trapping has been introduced in the calculation through

attenuation length λ [T. Raudorf, R. Pehl, NIM A255 (1987)].λ ~ 1/φ and depends on bias, detector temperature, crystal type

⎟⎟⎠

⎞⎜⎜⎝

⎛ −−⋅=

h

rrnnλ

'exp0

For GRETINA: φ = 1010 n/cm2 λ = 10 cmφ = 109 n/cm2 λ = 100 cm

Initial number of holes

Attenuation length

Distance traveled

Neutron damage

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Degradation in E resolution occurs for λ<100 cm, beforecorrection and for λ<30 cm, after correction, but only forλ<17 cm position resolutionbecomes worse than 1 mm (achievable limit).

A measurable effect of neutron damage on position resolution is never reached before annealing is required!

Results