A dvanced GA mma T racking A rray

AAdvanceddvanced GAGAmmamma TTrackingracking AArrayrray

Performance of an AGATA prototype detector estimated by Compton-imaging techniques

Francesco RecchiaINFN - Legnaro

on behalf of the AGATA collaboration

180 large volume 36-fold segmented Ge crystals packed in 60 triple-clusters

Digital electronics and sophisticated Pulse Shape Analysis algorithms

Operation of Ge detectors in position sensitive mode for -ray tracking

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

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

Design values: 5 mm of position resolution assumed

Triple cluster

Rint = 23 cm

Rext = 32 cm

The -ray spectrometer AGATA

180 HPGe

Pulse Shape Analysisto decompose

recorded waves

Highly segmented HPGe detectors

·

·

Identified interaction points

(x,y,z,E)i Reconstruction of scattering sequence from

Compton vertices

Digital electronicsto record and

process segment signals

1

2

3

4

ReconstructedReconstructed

gamma-raysgamma-rays

·

·

·· ·

·

· ·

Ingredients of -ray tracking

Pulse Shape Analysis concept

B4 B5B3

C4 C5C3

CORE

A4 A5A3

C4

D4

E4 F4

A4

B4

x

y

z = 46 mm791 keV deposited in segment B4

(10,10,46)

measured

(10,30,46)

Pulse Shape Analysis concept

B4 B5B3

C4 C5C3

CORE

A4 A5A3

C4

D4

E4 F4

A4

B4

x

y

z = 46 mm791 keV deposited in segment B4

(10,10,46)

measuredcalculated

Pulse Shape Analysis concept

B4 B5B3

C4 C5C3

CORE

A4 A5A3

C4

D4

E4 F4

A4

B4

x

y

z = 46 mm791 keV deposited in segment B4

(10,15,46)

measuredcalculated

Pulse Shape Analysis concept

B4 B5B3

C4 C5C3

CORE

A4 A5A3

C4

D4

E4 F4

A4

B4

x

y

z = 46 mm791 keV deposited in segment B4

(10,20,46)

measuredcalculated

Pulse Shape Analysis concept

B4 B5B3

C4 C5C3

CORE

A4 A5A3

C4

D4

E4 F4

A4

B4

x

y

z = 46 mm791 keV deposited in segment B4

(10,25,46)

measuredcalculated

Pulse Shape Analysis concept

B4 B5B3

C4 C5C3

CORE

A4 A5A3

C4

D4

E4 F4

A4

B4

x

y

z = 46 mm791 keV deposited in segment B4

(10,30,46)

measuredcalculated

Result of Grid Searchalgorithm

Pulse Shape Analysis concept

B4 B5B3

C4 C5C3

CORE

A4 A5A3

C4

D4

E4 F4

A4

B4

x

y

z = 46 mm791 keV deposited in segment B4

(10,25,46)

measuredcalculated

A test-beam experiment has been performed to measure this parameter in realistic experimental conditions

Simulations suggest that the overall performance

depends on the attainable position resolution

The position resolution required for the AGATA detectors

Setup of the in-beam experiment

BEAM 48Ti 100 MeV

TARGET 48Ti + 2H 220 μg/cm2

Si detectorDSSSD

Thickness: 300 μm

32 rings, 64 sectors

AGATA symmetric triple-cluster

d(48Ti,49Ti)p

Symmetric triple cluster

Silicon detector

Digitizers:

30 XIA DGF 4c cards

40MHz 14 bit

experiment performed at IKP of Cologne

Doppler correction using PSA results

Full statistics usedFull statistics used

32 keV

Doppler correction using PSA results

Full statistics usedFull statistics used

32 keV

11 keV

Doppler correction using PSA results

Full statistics usedFull statistics used

PSA algorithm: Grid Search

32 keV

11 keV

4.8 keV4.8 keV

2

3

4

5

6

7

8

9

0 1 2 3 4 5 6 7 8 9 10 11 12 13

position resolution FWHM [mm]

peak F

WH

M [keV]

Simulation vs Experiment

Grid Search

Recursive Subtraction

Matrix Method

Results obtained with different PSA

algorithm

Miniball Algorithm

Why Compton imaging?

15 days of beam-time to perform the test experiment

1 year of analysis PSA will be on-line

Need for a simpler procedure Need an prompt feed-back

from on-line analysis

Compton imaging

In-beam experiment: typical conditions

of future use

Compton imagingof a radioactive source inverse tracking

E1

E2

target

E1

E2

-source

Compton imaging performance

Error on Compton identification of source direction from:

Position resolution (axis) Energy resolution (scattering

angle) Compton profile

(scattering angle)

scattering angle [deg]

ang

ula

r er

ror

[deg

]

Imaging setup at LNL

AGATA prototype detector

TNT2 Digitizers: 4ch 14bit 100MHz

60Co source

Outline of analysis/simulation

Event selection

PSA

Position resolution

DAQ

Event selection

Smearing (position resolution)

Image formation

MC

Image formation

Comparison to simulation

E

E,pMC + E res + pos res Exp

MC + E resMC

≈

≈

Simple back-projections

Comparison to MC simulation

profile of experimental image

Monte Carlo + 5 mm position resolution

profile of experimental image

5.2

4.7

Experiment

[deg]

[d

eg]

[deg]

[d

eg]

pea

k F

WH

M[

deg

]p

eak

FW

HM

[d

eg]

position resolution FWHM[mm]

position resolution FWHM[mm]

CONCLUSIONS

Position resolution extracted by in-beam experiment and Compton imaging is 5 mm FWHM.

This value is in line with the design assumptions of the AGATA spectrometer, confirming the feasibility of -ray tracking.

AGATA will have a huge impact on nuclear structure studies (first phase of AGATA: LNL 2009…)

Possible applications of -ray tracking detectors to imaging.

Basic implementation of LMML

0 1

620

Compton imaging application