Recent developments in LaBr3 detectors for high energy gamma-rays

F. Camera University of Milano – INFN sez. of Milano

LaBr3 Scintillators

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BaF2

NaI

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LaBr3

L.Y. 63 ph/keVDecay Time 16 ns 380 nmN 1.9 = 5.3 g/cm3

RL (661 keV) 1.9 cm

FWHM

540 ps

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Luminosity (photoelectrons / MeV)

BGOGSO

Lu3Al

5O

12:ScLSOBaF

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YAlO3:Ce

CsI:Tl

NaI:TlCaI

2:Eu

LaBr3:Ce

LaCl3:CeTheoretical Limit

(Counting Statistics)

K2LaCl

5:Ce

RbGd2Br

7:Ce

High Interest in the Scientific Community (Base Science, Medical Imaging, Space Research)In 2007 more than 40 papers on LaBr3 / LaCl3 detectors published in IEEE and NIM

• Linearity, energy and time resolution tests

• Different PM tested at different voltages• Tests with and without the use of a preamplifier• Test with APD and HPD planned in future

• Response with high energy gamma rays

• PuC source - 6.13 MeV -rays• AmBe+Ni source - 8.98 MeV -rays• p (20 MeV) + C 15.1 MeV - Catania February 2008 -

• Natural radioactivity measurement

•Single and coincident measurements

• Particle Identification Measurements

•Particle identifications tests on LaBr3 and LaCl3

• Digitalization and PSA tests

• Signals acquired with 100 MHz – 2 GHz ADC• PSA algorithms tested for time, energy and PID

• Gamma Imaging with Segmented PMT

• PSF experimental Measurement • ISR Calculation and measurement

• GEANT simulations + Light tracking

• SHIDRA Light tracking code for Medical PET

Activities in Milano

• Voltage Stabilization• Temperature Effects • Voltage Divider Design

• F.Camera et al. CR – IEEE - 2007

• F.C.L.Crespi et al. – IEEE - 2008

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

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

High energy -rays measurements with LaBr3

• LaBr3 Gain Stability and Linearity

• Critical especially for E > 5 MeV

• Measurements of mono-energetic high energy -rays

• Doppler Broadening – Imaging

• PMT – VD and other photo-sensors

• Digital Electronics

• How a LaBr3 Array can complete/compete with an HPGe array

LaBr3 Gain Stability and Linearity

Energy resolution: 19 keV at 662 kevTime resolution: 230 ps (intrinsic)

The light yield in of LaBr3 crystal is too high

for standard PMT tubes

• Linearity • Temperature drift• Voltage drift

These effects are ‘new’ for scintillator physics. LaBr3 crystals, because of light output) are the only with resolution below 3% at 661 keV

• The tube must be used at low voltage

• Not optimal performances of Tubes

• Bad timing

• New special designed voltage divider (Milano INFN Electronic workshop).

The VD takes energy signal at 6° dinode and pre-amplify it. Time signal is taken from anode (on tests).

Test at LNS – 12C(p,p’)12C Beam time February 2008

The light yield in of LaBr3 crystal is too high

for standard PMT tubes

• Linearity • Temperature drift• Voltage drift

These effects are ‘new’ for scintillator physics. LaBr3 crystals, because of light output) are the only with resolution below 3% at 661 keV.

Energy resolution: 19 keV at 662 kevTime resolution: 230 ps (intrinsic)

The scintillation properties of LaBr3 do not show a dependence on temperature

… but the PMT do

• Linearity • Temperature drift• Voltage drift

• Temperature effects can deteriorate resolution

• The Dependence is Linear, gain drift approximately - 0.5 % for degrees

• If temperature is monitored the drift can be corrected (only a small hysteresis) is present

• There is a initial period of temperature stabilization which is not possible to correct

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Temperature Voltage Divider

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LaBr3 Gain Stability and Linearity

Energy resolution: 19 keV at 662 kevTime resolution: 230 ps (intrinsic)

PMT gain is very sensitive to voltage. Excellent energy resolution requires

voltage stabilization

• Linearity • Temperature drift• Voltage drift

• The HV unit should provide voltage with a stability below 0.01 %

• Not all HV units commonly used for scintillators can provide such stability

• Event by Event measurement of HV ?

3' x 3' LaBr3 Photonics XP5300 (700 V)

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LaBr3 Gain Stability and Linearity

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HV = 590 V

Energy Resolution

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Energy (MeV)

AmBe-Ni source

8.89 MeV -ray

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PuC source

6.13 MeV -ray

2nd escape peak

1st escape peak12C(p,p’)12C* LNS Catania

Measurements of mono-energetic high energy -rays

Measurement in Catania12C(p,p’)12C* Am-Be-NiPuC

Measurements in MilanoAm-Be-Ni

Joint Proposal ESA-MILANO-LNSfor beam time in 2009

Breakthrough in PMTdevelopment

Photonics - Clarity Hamamatsu - SBA

• There are two new type PMT tubes on market

• Photonics – Clarity Class• Hamamatsu SBA-UBA class

• In this tubes the quantum efficiency is up to 45%

New Technology on PMTs

Tests using these two kind of tubes are now running in Milano

Doppler Correction – Imaging

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

.. but

• they substand a large solid angle

• this will affect energy resolution

LaBr3 4’x 8’ placed at 20 cm from target

1 MeV -rays source v/c = 0.1

Is it possible to localize the interaction Points ?

E=1 MeVBeta = 0.1, d=20 cm

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Angolo (lab system)

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Doppler Correction – Imaging

• Segmented Phototubes

• 6mm x 6mm segments

• Medical Imaging Techniques

Charge distribution sampling by anode

array

Scintillation light flash on photocathode

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Projected charge

Doppler Correction – Imaging

• The PSF function at 140 keV has been measured for a 1’ x 1’ LaBr3 *

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• The PSF function at 140 keV will be measured for a 3’ x 3’ LaBr3

• Full Simulations are now running to extract the ISR• GEANT + SCIDRA (-rays interactions + light transport)**

• The higher the energy of -rays the better will be the localization*Thanks to R.Pani and M.Cinti - INFN and Policlinico of Rome** Thanks to C.Fiorini from Milano Politecnico

Segments

PSF

Digital Electronics

The prototype of the VME digital board has been built and tested in a Kmax environment

2 channels for time1 channel for energy

The performance for BaF2 andLaBr3 detectors are as expected • Energy Resolution• Time Resolutions• Fast vs Slow Rejection (for BaF2)

New (final) version of a 4 channel board digital board for BaF2 and LaBr3 scintillators will be built in 2009.

Energy Resolution Time Resolution

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60Co FWHM 2.3%

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60Co Source

General performances for time resolution using the digital board and an analogue card with a 14 bits 100 MHz ADC

- Using Pulser 125 ps- Using two signals from one LaBr3 crystal 550 ps (Thr. = 150 keV HV = 450 V)

- Using two BaF2 crystals 600 ps (Thr. = 150 keV )

Digital Electronics

A LaBr3 array for spectroscopy can complete an HPGe Array in several physics cases

• Very high background• Few transitions• Extremely rare events• High energy -rays

• ‘Low’ Budget• Simple experimental setup

4’ x 10’ LaBr3 at IEEE-2007

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Gamma Ray Energy [MeV]

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4’ x 8’ LaBr3 Array at 20 cm

A LaBr3 array for -spectroscopy can complete anHPGe Array in several physics cases

• Efficiency Higher in LaBr3 array

• Crystals are much larger and much cheaper

• Time resolution much better in LaBr3 array

• 500 ps vs 10 ns time resolution• TOF measurements isolate ‘ 10 cm source ‘ vs ‘ 3 m source’

• Maintenance

• No cooling • No vacuum• No FET

• Energy Resolution HPGe detectors are 10 times better

• 25 keV vs 2 keV

• Doppler Broadening

• in HPGe it is possible to perform Gamma ray Tracking• Gamma Imaging in large LaBr3 ?

• Spatial Resolution will be much worse than in HPGe

Thank you