Recent developments in LaBr 3 detectors for high energy gamma-rays F. Camera University of Milano – INFN sez. of Milano
Jan 11, 2016
Recent developments in LaBr3 detectors for high energy gamma-rays
F. Camera University of Milano – INFN sez. of Milano
LaBr3 Scintillators
800 900 1000 1100 1200 1300 14000
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BaF2
NaI
arb.
uni
ts
Energy (keV)
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
0%
2%
4%
6%
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12%
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En
erg
y R
eso
luti
on
@ 6
62 k
eV (
fwh
m)
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
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
Ba
ric
en
ter
[ke
V]
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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Drift (Volts)
Dri
ft (
ke
V)
LaBr3 Gain Stability and Linearity
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Energy [MeV]
FW
HM
(ke
V)
HV = 625 V
HV = 590 V
Energy Resolution
7.0 7.5 8.0 8.5 9.0 9.5 10.00
200
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800
1000
coun
ts
Energy (MeV)
AmBe-Ni source
8.89 MeV -ray
4.0 4.5 5.0 5.5 6.0 6.5 7.0
400
600
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1000
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coun
ts
Energy (MeV)
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)
FW
HM
(k
eV)
.
Doppler Correction – Imaging
• Segmented Phototubes
• 6mm x 6mm segments
• Medical Imaging Techniques
Charge distribution sampling by anode
array
Scintillation light flash on photocathode
i
in
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
0.50 0.75 1.00 1.25 1.50 1.75 2.000
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C
ount
s
Energy (MeV)
60Co FWHM 2.3%
0.3-0.5 0.5-0.7 0.7-0.9 0.9-1.1 1.1-1.50.2
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Intrin
sic
Tim
e R
esol
utio
n (n
s)
Energy Window (MeV)
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]
Ab
so
lute
FE
P e
ffic
ien
cy 4 LaBr3
8 LaBr3
12 LaBr3
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