Large Volume LaBr3:Ce for high energy γ-rays

B. Million INFN sez. of Milano

Physics CasesNuclear Structure – Gamma Spectroscopy

• Measurements of highly collective states

• High energy γ-rays from the decay of the GDR and GQR in exotic nuclei

• High energy γ-rays from the decay of the GDR in hot rotating nuclei

• Measurements of first excited states of nuclei far from the valley of stability

Valley ofStability

HECTOR arrayDeveloped and built in the 90’ and still in operation

• 8 Large Volume BaF2 crystals

HECTOR arrayDeveloped and built in the 9l0’ and still in operation

• 8 Large Volume BaF2 crystals

• Diameter 14.5 cm• Thickness 17 cm

• Time Resolution ≈ 600 ps• Energy Resolution ≈ 15%

at 662 keV• Fast vs Slow ð

Particle-γ discrimination• Scintillation light at 220 nm

- PMT with quartz window• Compact and portable

(we have measured using HECTOR in 9 different laboratories)

• Low light yield ðNo position sensitivity

0%

2%

4%

6%

8%

10%

12%

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

Ener

gy R

esol

utio

n @

662

keV

(fw

hm)

Luminosity (photoelectrons / MeV)

BGOGSO

Lu3Al

5O

12:ScLSOBaF

2

YAlO3:Ce

CsI:Tl

NaI:TlCaI

2:Eu

LaBr3:Ce

LaCl3:CeTheoretical Limit

(Counting Statistics)

K2LaCl

5:Ce

RbGd2Br

7:Ce

P.Dorembos et al NIM A486(2002)208

• CeBr3 – 4% at 662 keV• SrI3 – 3% at 662 kev (2.3% expected)• CLLC – 3% at 662 keV• CLLB – 3% at 662 keV• Garnet – 4% at 662 keV

New Scintillators

LaBr3:Ce Scintillators

800 900 1000 1100 1200 1300 14000

1

2

3

4

5

BaF2

NaI

Energy (keV)

LaBr3L.Y. ≈ 63 ph/keVDecay Time ≈ 16 nsλ ≈ 380 nmN ≈ 1.9 ρ = 5.3 g/cm3

RL (661 keV) 1.9 cm

FWHM

540 ps

60Co

Large Interest in scientific community• In 2007 more than 40 papers on LaBr3 / LaCl3

detectors published in IEEE and NIM• Workshop last week: space, medical, plasma

PARIS project from Spiral2

Large Volumes recently available in our group:

1 - 1”x1” LaBr3:Ce1 - 1”x1” LaCl3:Ce1 - 3”x3” LaBr3:Ce2 – 3.5”x8” LaBr3:Ce

• Linearity, energy and time resolution tests• Different PMT tested at different voltages• Voltage Stabilization• Temperature Effects • Voltage Divider Design

• Response with high energy gamma rays• PuC source - 6.13 MeV γ-rays• AmBe+Ni source - 8.98 MeV γ-rays• p (20 MeV) + C ⇒ 15.1 MeV - Catania February 2008 –• p (20 MeV) + C ⇒ 15.1 MeV - Catania May 2009 –

• Internal radioactivity measurement• Single and coincident measurements

• Particle Identification Measurements• Particle identifications tests on LaBr3 and LaCl3

Activities in Milano

• F.Camera et al. – IEEE - 2007

• F.C.L.Crespi et al. – IEEE – 2008• F.C.L.Crespi et al. NIM-A 602(2009)520

• R. Nicolini et al. NIM A582(2007)554

• N.Blasi et al. – IEEE - 2009

• Digital/Analogical board development • Signals acquired with 100 MHz – 2 GHz ADCs• PSA algorithms tested for time, energy and PID

• Gamma Imaging with Segmented PMT• 1”x1” + Segmented PMT

• PSF Measurement• Spatial Linearity Measurement• Response to collimated beam of 662 keV γ-rays• Event by Event analysis for the identification of the IPs

• 3”x3” + Shielded PMT

• PSF Measurement• Spatial Linearity Measurement

• Simulations + Light tracking• GEANT3 + SHIDRA - Gamma + Scintillation Light tracking• GEANT4 - Gamma + Scintillation Light tracking

• S.Brambilla et al. – IEEE – 2007• S. Riboldi et al. – IEEE – 2007• S. Brambilla et al. – IEEE 2008

• F.Birocchi et al. IEEE – 2009

• F.Birocchi et al. IEEE – 2009

3” x 3” 3.5” x 8”

about 19-20 keV at 662 keV Good ∆E about 21-24 keV at 662 keVGood ∆t < 1 ns

• Photonis PMT are better for linearity and ∆t• Hamamatsu PMT with SBA cathode (higher Q. E.)

are better for ∆E are not better for ∆E !BUT Photonis closed PMT production !!!

Needs for high Voltage for good linearity ] Needs for a PMT with less than 8 dinodes Needs for lower gain for good ∆t ] or for special Voltage Divider.

3.5” x 8” LaBr3:Ce Response to High Energy γ-rays

Measurement in Milano and Catania (LNS) 12C(p,p’)12C* Am-Be-NiPuC

-PMTs gain fluctuations still affect Energy Resolution measurements

- Non-Linearity

BaF2 14.5 cm x 17 cm LaBr3:Ce 9.5 cm x 20 cm

≈ 1.4 MeV

Doppler Broadening simulation• Large Crystals give large efficiency for high energy γ-rays (16% at 10 MeV)

but they cover a large solid angle and this will affect energy resolution with fast moving source

1 MeV γ-rays source v/c = 0.1 FWHM (60 ) ≈ 30 keV

1 MeV γ-rays source v/c = 0.5 FWHM (60 ) = 160 keV

Eγ=1 MeVBeta = 0.1, d=20 cm

20

25

30

35

40

0 100 200Angolo (lab system)

FWH

M (

keV)

.

LaBr3:Ce 4”x 8” placed at 20 cm from target1 MeV γ-rays source v/c = 0.1

Doppler Broadening Correction – Detector Position Sensitivity -

• Segmented Phototubes• Position Sensitive light Sensor

• SiPMT or d-SiPMT• Silicon Drift Detectors

1” x 1” LaBr3:Ce crystal + 3” x 3” LaBr3:Ce crystal +H8500C-100 Mod 8 phototube R6233 shielded phototube.

The detectors have the surfaces treated to fully reflect the scintillation light to have the best possible energy resolution

3” x 3” LaBr3:Ce crystal + shielded R6233

Collimated 662 keV Source

As expected, the energy resolution improves as the window size increases

The Point Spread Function for different collimated γ-ray beam positions shows that position sensitivity is achievable also in 3” x 3” crystals

Work is in progress for more accurate measurements and algorithms

Full PMT

1” x 1” LaBr3:Ce crystal + H8500C-100 Mod 8x8 phototube662 keV collimated beam

Mapping centroid positions over the 16 segments covering the 1”x1” LaBr

-15

-10

-5

0

5

10

15

-15 -10 -5 0 5 10 15

Cen

troi

d's p

ositi

on (m

m)

Source’s position (mm)

LaBr3 1”x1” - 662 keV

Current developments on position sensitivity:

- Event by event analysis of 662 gamma images is possible

- New algorithms are developed

- 3”x3” with segmented PMT is on the way

- GEANT3+SHIDRA or GEANT4 simulations with scintillation light transport is being done

Scintillators, electronics and processing

Scintillators PMTs

Analog spectroscopy systemEnergy

Time

PSD

Energy

Time

PSD

PSDDigital algorithms for PSD

Photomultiplier

voltage divider networkBetter linearity

Mixed A/D spectroscopy system

BaF-Pro Electronics

• 16 Channels Acquisition System for Scintillation Detectors developed in Milano

• NIM standard module• Provides:

– Energy (< 1%)– Time (through CFD, < 100 ps)– PSD (through fast vs slow technique)

• Designed for BaF2 scintillators– PSD technique matches their signal

characteristics very well• Preliminary results also for LaBr3

PSD with BaF-Pro Electronics

BaF2 LaBr3

Alpha

Alpha

GammaGamma

Fast component: integrated input signal (up to peak of pulse)Slow component: integrated input signal (up to end of pulse) = energy

Fast Fa

st

SlowSlow

Scintillators, electronics and processing

Scintillators PMTs

Analog spectroscopy systemEnergy

Time

PSD

Energy

Time

PSD

PSDDigital algorithms for PSD

Photomultiplier

voltage divider networkBetter linearity

Mixed A/D spectroscopy system

• Suitable for LaBr3 and BaF2

• 2-Channels Board (VME bus)• Mother Board

– DSP (TI TMS320C6203)– FPGA (XILINX XC4VSX35)

• Piggy-Back Boards (not shown)– A/D converter: 100 MHz, 14 bits– Shaping filter: 2 poles at 25 ns– Analog front-end (variable gain)– Discriminators

Mixed A/D Electronics forScintillation Detectors

Experimental results with LaBr3

ENERGY MEASUREMENT• Pulse signals integrated over time• Energy resolution: 2.3% @ 1.33 Mev

TIME MEASUREMENT• 100 MHz free running ADC• Digital signal processing of pulses

– Optimum FIR Filter in DSP• 630 ps FWHM (coincidence)

time resolution @ 1.33Mev

Scintillators, electronics and processing

Scintillators PMTs

Analog spectroscopy systemEnergy

Time

PSD

Energy

Time

PSD

PSDDigital algorithms for PSD

Photomultiplier

voltage divider networkBetter linearity

Mixed A/D spectroscopy system

LaBr3:Ce 1”x1” (2 GHz, 12 bits ADC)

Digital Algorithms for PSD:Application to internal radioactivity and natural

background spectra

BaF2(100 MHz, 14 bits ADC)

CONCLUSION

A LaBr3:Ce detector array can increase the efficiency and the power of an HPGe Array in several physics cases and is effective also in a standalone configuration

• Detector Properties Measurements• Response to high energy γ-rays • R&D on PMT and Voltage Dividers• R&D on electronics (analog and digital) • R&D on PSA• Position Sensitivity of large volume crystals

• When coupled with AGATA (in a 1 or 2π configuration) they will significantly increase the physics performance of the array – first LaBr detectors used in test run in LNL (Silvia’s talk)

• Large volume LaBr3:Ce detectors are specific and, for the moment, unique for the measurement of high energy γ-rays.

• An array of few detectors will be easily transportable and can be efficiently moved through different laboratories if required

• New scintillators with excellent properties have appeared and some additional R&D is required to better understand their properties

R. Avigo, F. Birocchi, N. Blasi, C. Boiano, A.Bracco, S. Brambilla, J. Brosamer, F.Camera, F. Coniglio, F.C.L. Crespi, A. Idini, B.M., R. Nicolini, L. Pellegri, S. Riboldi, O. Wieland

M.N. Cinti and R. Pani Dipartimento di Medicina Sperimentale, Università di Roma “La Sapienza”, Roma

C. Fiorini and A.MaronePolitecnico di Milano and INFN, Piazza Leonardo Da Vinci, 20133 Milano

D. Santonocito, C.Maiolino, G.Bellia and A.Rosa, INFN laboratori Nazionali del SUD, Catania, Italy

A.Owen and F.QuaratiAdvanced Studies and Technology Preparation Division (SCI-PA) ESA/ESTEC Keplerlaan 1, 2201AZ Noordwijk, the Netherlands

Milano LaBr3:Ce team

Thanks also to

Thank you

3” x 3” LaBr3:Ce Response to High Energy γ-rays

Measurement in Milano and Catania (LNS) 12C(p,p’)12C* Am-Be-NiPuC

- PMTs gain fluctuations still affect EnergyResolution measurements

- Non-linearity

1” x 1” LaBr3:Ce crystal + H8500C-100 Mod 8 phototube.

On an event by event basis the segment which has measured the highest signal is selected

An event by event position sensitivity is achievable

No Collimated Source

-7 mm Collimated Source +7 mm Collimated Source+1 mm Collimated Source

Simulations: γ-rays interaction + scintillation light transport

Collimated + 12 mmNo Collimation

• GEANT3 + SCIDRA• GEANT4

Open Problem: A correct description of reflected light is critical in the simulations. Unfortunately the reflective treatment/properties of LaBr3:Ce detector surfaces is not known and, in the data, we have some excess of scintillation light in the lateral segments which we cannot reproduce in simulations.

Natural Radioactivity measurements• In singles LaBr3 1”x1”:

Internal Radioactivity

227Ac decay chain

• τ ∼ 1011 years• ∼ 0.1 cts/sec/cm3

• low energy γ-rays in Coincidence

- Alpha emission (1.5-3 MeV) - beta emission (0-1.4 MeV)

138La decay chain

EC ⇒ 1432 keV γ-rayβ decay ⇒ β + 789 keV γ-ray

- γ escape → 0-250 kev beta- γ interacts →780-1000 kev

summed signal Activity ∼ 0.7 cts/sec/cm3

Structure of 1432-1469 keV

peak

R. Nicolini et al. NIM A582(2007)554

LaBr3 (keV)

HPG

e (k

eV)

αemission

• In coincidence:

• HPGe – LaBr3 γ−γ Matrix

0 100 200 300 400 5000

100

200 219Rn 211Bi 227Th 223Ra

Coun

ts

Energy (keV)

α emission