Fast inorganic scintillators - Positron Annihilation in Halle

Fast inorganic scintillators
- status and outlook -
R. W. Novotny
2nd Physics Institute
University Giessen
• scintillator basics and history
• cross luminescence BaF 2
• Ce 3+ luminescence centers
• PbWO 4
• inorganic scintillator fibers
• outlook

asic concept of a scintillation detector
X rays gamma
rays
heavy charged
particles
thermal neutrons
energetic neutrons
Photoelectric effect
Compton effect
Pair production
Bethe Bloch
e
scintillator
nuclear reaction
proton
ionization
excitation
many
e-h pairs
request for a wide spectrum of detector materials

Number of dicovered scintillators
history
Quantity of principal inorganic scintillators
discovered
4
3.5
3
2.5
2
1.5
1
0.5
0
investigation of
Photomultiplier
Curran / Baker
X-ray imaging
screens
a -scattering
SrI 2:Eu 1968/2008
LSO:Ce,Ca 2007
LuI 3:Ce 2003
LaBr 3:Ce 2001
LYSO:Ce 2001
LuYAP:Ce 2001
LaCl 3:Ce 2000
LuAP:Ce 1994
LSO:Ce 1982
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Years
Alcali-Halides
Oxides
M.Korzhik, 2003
year
discovery and development
of new scintillator materials
are strongly correlated with basic research and technology in physics ...
M.J.Weber
J. of Lum. 100 (2002) 35

inorganic scintillators
large variations in:
• compactness
• luminescence yield
volume: 1X 0 3
pulse height / mV
time / ns

asic processes luminescence center
basic processes in
inorganic scintillator
ionic crystal
host material
E gap > ~ 4 - 12 eV
e
h
thermalization
luminescence centre
intrinsic or
dopant
transport
conduction band
luminescence
valence band

… but it is more complex !
e
h
thermalization
1 - 100 ps
Trap
radiationless
recombination
thermalization
thermally released
Shallow trap
fast to slow
(afterglow)
Defect
transfer or
luminescence
estimation of achievable light yield:
conduction band
Y
direct excitation
relaxation
LC
valence band
> ns
E
E
luminescence
gap
S
Q

interplay of excitation and emission …
… and optical transparency of the material

achievable energy resolution
can be further optimized by matching to photo sensor

most scintillators are sensitive to temperature
thermal quenching !

achievable energy resolution not only determined by
photon statistics !?
but:
resolution at 662 keV / %
10
8
6
4
2
BaF 2 BGO
YAlO 3 :Ce
Lu 3 Al 4 O 12 :Pr
LSO:Ce
CsI:Tl
NaI:Tl
LaCl 3
R stat
LaBr 3
SrI 2 :Eu
0
0 5.000 10.000 15.000 20.000
number of detected photons at 662 keV
linear response of the scintillator, index of refraction, light
collection, quantum efficiency and linearity of sensor, etc.

non-proportionality
and
energy resolution
typical examples
Relative light yield
Energy reslution at FWHM (%)
1.2
1.1
1.0
0.9
10
LaBr 3:Ce
NaI:Tl
10 100 1000
Energy (keV)

how everything started: R.Hofstadter, Phys.Rev. 74 (1948) 100
NaI
with source
NaI
without source

BaF 2
kinetics of the two fast
scintillation components
at l 195nm and l 220nm
ideal for fast timing:
• fast rise time
• fast decay time
• sufficient light yield
timing determined by arrival of
first photons at sensor
P.Schotanus et al., NIM A259 (1987) 586

fast slow component
BaF 2
both luminescence components show a
different temperature dependence
different scintillation
mechanisms
slow component:
strongly temperature dependent
determines energy resolution
dY/dT-1.4%/ 0 K

BaF 2: fast UV luminescence
E gap
E VOC
fast
STE
CondB
ValB
Core-Valence
Luminescence CVL
OCoreB
Yu.M. Aleksandrov et al, Sov. Phys. Sol. State 26 (1984) 1734
6s, 5d Ba 2+
2p F -
5p Ba 2+
Ionic crystal
E VOC < E gap
Auger-free luminescence
Cross luminescence

• identification via pulse shape analysis PSA
due to intrinsic luminescence properties:
scintillation components show different response to
electromagnetic or hadronic probes CsI(Tl), BaF 2, ...
proton
photon
fast component
time
total light output
signal integration width
plastic
VETO
E-fast E-fast
BaF 2-detector
photons photons
protons protons
E-total
identification of charged
and neutral events

time-of-flight / ns
particle ID:
• time-of-flight
BaF 2 (TAPS)
2 AGeV Ca+Ca
energy / MeV
E (MeV)
250
200
150
100
50
0
C
0
X ...
0 2 4 6 8 10
t (ns)
time resolution: s t > 85 ps

Time-of-flight PET
detector concept
achieved position resolution
S.Tavernier et al., BaF 2 with MWPC-TMAE readout

TAPS
511 modules
counts
A2@MAMI
Mainz
tagged photon
facility
E < 1.5GeV
on-line data
invariant mass / MeV
complete
new readout

CVL candidates
E gap 4 - 13 eV
Condition for CVL
E VOC < E gap
Ca 2+
P.A. Rodnyi, Sov. Phys. Solid State 34(1992)1053
I
Br
Cl
F
E VOC
Sr 2+
C.W.E. van Eijk, Nucl. Tracks. Radiat. Meas. 21(1993)5
CVL
17 eV 13 eV 8 eV 10 eV 7.5 eV 4.5 eV
Rb +
Ba2+ Rb
K + +
Ba2+ K +
decay time ~ 1 ns
Cs + Cs +
F, Cl, Br, I
CondB
ValB
OCoreB
light yield 2000 photons/MeV

Ce 3+ luminescence center
Core +
1 electron in
4f state
e
excitation
h
Ce 3+
relaxation
conduction band
5d
4f
emission
valence band
5d 4f allowed dipole transition
fast response ~ 20 ns

Ce 3+ luminescence center
Ce 3+ relaxation Stokes shift
energy
0.1 fs
1 ps
quenching
> ns
configuration coordinate
4f levels shielded
no line broadening
Rodnyi
Intensity (arb. units)
C3h
5.10 eV
4.96 eV
4.71 eV
4.52 eV
4.41 eV
Exc.
6.2 eV
5d
S=5900 cm -1
150 200 250 300 350 400 450
Wavelength (nm)
4f
LaCl 3:0.57%Ce
3.68 eV
3.46 eV
1740 cm -1
broad
emission lines
C. van Eijk

additional candidates
ion ground state notation excited state
La 3+ Xe configuration
(closed shell)
Ce 3+ ,, + 1 4f electron 4f 1 4f 0 5d 1
Pr 3+ ,, + 2 4f electrons 4f 2 4f 1 5d 1
Nd 3+ ,, + 3 4f electrons 4f 3 4f 2 5d 1
…
Eu 2+ (half filled shell) + 7 4f electrons 4f 7 4f 6 5d 1
Gd 3+ (half filled shell) 4f 7
…
Lu 3+ (closed shell) + 14 4f electrons 4f 14

fast scintillation mechanism
Ce 3+ 5d 4f
in favourable host
Y
E
E
Egap LY
Egap l
gap
~ 20 ns
S
Q
matching light sensor
timing properties:
1
E [eV]
n
l
3
12
10
8
6
4
2
0
see papers by P. Dorenbos
Ce 3+ levels and Egap
free ion
2 n
3
fluorides
chlorides
2
bromides
2
iodides
5d
oxides
E gap
Ce 3+ E 5d-4f
sulfides
selenides
4f
2

K 2LaX 5:0.7% Ce 3+ (X = Cl, Br, I)
scintillation decay
lifetime from Cl to Br to I
emission
wavelength from Cl to Br to I

LaCl 3:Ce 3+ scintillation decay
Intensity (a.u.)
25 ns
10% LaCl3 :Ce 3+
30%
LSO
NaI:Tl
0 200 400
Time (ns)
600 800 1000
NaI:Tl
230 ns
Lu 2SiO 5:Ce
40 ns

LaCl 3:Ce 3+ energy resolution
Intensity (a.u.)
55 Fe
R=42%
0 5 10
241 Am
R=10.5%
50
Energy (keV)
E.V.D. van Loef, P. Dorenbos, C.W.E. van Eijk, K.W. Krämer, H.U. Güdel
Appl. Phys. Lett. 77 (2000) 1467
100
137 Cs
500
R=3.3%
800
50,000
photons/MeV
NaI:Tl
40,000
photons/MeV
Lu 2SiO 5:Ce
26,000
photons/MeV

LaCl 3:Ce 3+
4“ x 6“
4 x 6 mm 2
Counts
32keV Ba
400 500 600 700 800
La X-ray escape peak
0 200 400 600 800
Energy (keV)
E/E=4.1%
E/E=3.1%
E.V.D. van Loef, P. Dorenbos, C.W.E. van Eijk,
K. W. Krämer, H.U. Güdel,
Appl. Phys. Lett. 77 (10) (2000) 1467.

LaBr 3: 5%Ce 3+
counts (arb. units)
1.2
1.0
0.8
0.6
0.4
0.2
61,000 ph/MeV
R=2.9%
0.0
0 100 200 300 400 500 600 700 800
380
Pulse height spectrum 662 keV gamma rays
NaI:Tl
2.8 % FWHM
6.5 % FWHM
energy (keV)
energy resolution
light yield
70,000 photons/MeV
(NaI:Tl 40,000 ph/MeV)
decay time
16 ns
(NaI:Tl 230 ns)
E.V.D. van Loef, P. Dorenbos, C.W.E. van Eijk, K.W. Krämer,
H.U. Güdel
Appl Phys Lett 79(2001)1573

LaBr 3:Ce 3+ decay time and time resolution
intensity, normalized
10 0
10 -1
10 -2
10 -3
decay time 16 ns
rise time faster
0 50 100 150 200 250
time, ns
0.5%
5%
10%
20 %
30%
511 keV - 511 keV
t < 300ps
courtesy Kanai Shah, RMD

LaBr 3:Ce 3+
345 cm 3 volume
380
Counts
6000
5000
4000
3000
2000
1000
BrilLanCe 380 3x3
137 Cs
FWHM
3.00%
0
0 200 400 600 800 1000
channel

Lanthanum halides:
X-ray excited optical luminescence
LaCl 3:Ce 3+
• Ce concentration , light yield
• Ce concentration , host emission
LaBr 3:Ce 3+
• Ce concentration , light yield

some scintillator specs
Density
g/cm 3
Attenuation
length at
511 keV
mm
Photoel
effect
%
Light yield
phot/MeV
Decay time
ns
Emission
max
NaI:Tl 3.67 29.1 17 41,000 230 410
Bi 4Ge 3O 12 (BGO) 7.1 10.4 40 9,000 300 480
Lu 2SiO 5:Ce (LSO) 7.4 11.4 32 26,000 40 420
Lu 2(1-x)Y 2xSiO 5:Ce (LYSO)
X = 0.1
7.1 12 30,000 40 420
LuAlO 3:Ce (LuAP) 8.3 10.5 30 11,000 18 365
Lu xY 1-xAlO 3:Ce (LuYAP)
X = 0.2
LaCl 3:Ce 3.86 28.0 14.7 46,000 25 (65%) 350
LaBr 3:Ce 5.07 22.3 13.1 70,000 16 (97%) 380
LuI 3:Ce 5.6 18.2 28 90,000 6-140 (72%) 472, 535
new generation of dense, bright and radiation hard scintillators
nm

PbWO 4: a fast scintillator - but with low light yield
counts
Counts
100000
10000
1000
100
10
1
10000
8000
6000
4000
2000
T = +6 0 C
Improved PWO crystal
0 100 200 300 400 500 600 700 800 900
T = -7 0 C
time, ns
T = -22 0 C
T = -30 0 C
0
100 200 300 400 500 600 700 800
light yield / a.u.
t1= 6.5 ns D1= 97%
t2= 30.4 ns D2= 3%
60Co
strong temperature quenching
counts
counts
3000
2500
2000
1500
1000
500
0
3000
2000
1000
0
200 400 600 800 1000
light yield / a.u.
137 Cs
s/E=14,5%
s/E=16.9%
200 400 600 800 1000
light yield / a.u.
22 Na
s/E=10.9%

E, cm -1
PbWO 4: a fast scintillator - but with low light yield
3T 3
1, T2
WO 4 2-
3.9 eV 3 eV
1 A1
Energy levels of dopings
Donor
R
Acceptor
doped PWO:Y, La,Mo
the shallow WO 4 3- + La centre is an
additional radiating centre
prevents e - to be trapped by deep
Mo centres
suppresses afterglow and large part
of slow components
pure PbWO 4
non radiative losses in PWO
temperature quenching
of WO 4 2- luminescence
WO 4 2-
3.9 eV 3 eV
1 A1
e -
0.2 eV
1 A1
WO 4 3- +La
3 eV
1 A1
MoO 4 3-
2.5 eV

device crystal modules
CMS
ECAL
E
s
10 3
depth
X 0
photosensor B
T
where beam energy
PbWO 4 82 26 APD/VPT 4 LHC 7
0.
5%
@120GeV
TeV

the PANDA detector at FAIR
• photon detection with high resolution
over a large dynamic range:
10MeV < E < 15GeV
• high count-rate capability (2∙107 barrel
~11.000
Annihilations/s)
• nearly 4 coverage
• sufficient radiation hardness endcaps
• timing information for trigger-less DAQ ~4.000 concept
Target Spectrometer
PWO-II
200mm (23X o)
crystals
4 detector for spectroscopy and reaction dynamics with antiproton

the Target Spectrometer:
based on high-quality PWO-II

optical transmission light yield @RT
radiation
hardness

prototype performance
extension
response
to
to
energies
high energy
< 50MeV
photons
@ MaxLab
energy resolution s
tagged photon
facility
@ MAMI, Mainz
E= 26 MeV
e -
‘s
64 MeV < E 1.5 GeV
E =43.3MeV
readout with incident energy / GeV
photomultiplier
• optimized light output: PWO-II
• cooling: operation at T=-25 o C
readout with
photomultiplier

eadout via SADC: further improvement
time resolution
1 ns
energy-resolution
( 3x3 matrix )

consequences of cooling:
• fast decay kinetics even at T=-25 o C
LY(100ns)/LY(1µs) > 0.9
• constant ratio
LY(-25 o C)/LY(+18 o C) = 3.9
•„no“ recovery of radiation damage at T=-25 o C
asymptotic light loss correlated with k (RT)
T= -25°C
rel. light loss @ 25 o C / %
k @ RT / m -1

ecovery of radiation damage @RT
∆k (420 nm) / m -1
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
@RT
0 50 100 150 200
illumination time / min
Spontaneous
LED_1550nm
LED_1300nm
LED_1060nm
LED_940nm
LED_464nm
0 200 400 600 800 1000 1200 1400 1600
applied integral dose of 60 Co: D = 30Gy
recovery of normalized light yield / %
100
90
80
70
60
50
@T= -25 o C
illumination time / min
470 nm
525 nm
640 nm
840 nm
935 nm

technology: micro-pulling-down technique (µPD)

material density
LuAG
:Ce
g/cm 3
Lu 3Al 5O 12:Ce 3+
Z eff
emission
wavelength
nm
index of
refraction
decay
time
ns
light
Yield
ph/MeV
6.7 63 530 1.84 50-100 15.000
emission spectra at various
positions: slight changes
tested fibers: 0.45mm - 2.0mm

esponse to 241 Am - single sided readout
Ø 1.0 mm fiber
~
e
-μd
LuAG:Ce
additional wrapping with teflon increases the light yield by ≈ 70 %

esponse to 241 Am - coincidence readout
fiberlength between 2.5 cm and 4.5 cm
time resolution of a single PMT:
(deduced from left - right coincidence)
σ Δt
t
2
LuAG:Ce

improvement of technology
• efficiency
• reproducibility
• multi-pulling
• packaging
simultaneous growth of
7 LuAG fibers
100 mm
20 fibers of
comparable quality
LuAG:Ce

material density
g/cm 3
Z eff
emission
wavelength
nm
index of
refraction
decay
time
ns
light
Yield
ph/MeV
LYSO 7.4 66 420 1.81 40 27.000
Lu 2(1-x)Y 2xSiO 5:Ce 3+ tested fibers: 0.6mm - 2.0mm
emission spectra: Ø 0.6mm
- nearly constant emission
- severe attenuation

LYSO:Ce fiber (Ø = 0.3 mm, L = 100 mm)
response to 241 Am - single sided readout
average attenuation coefficient:
μ ≈ (0.68 ± 0.02) cm -1
LuAG:Ce (Ø 0.3 mm): μ ≈ (0.85 ± 0.06) cm -1
μ
μ
0.68
0.018
cm
-1
cm
-1
LYSO:Ce
good homogeneity
of all investigated fibers

LuAG:Ce fibers
100 mm long
1 mm diameter
round

SiPM readout – PET application
KVI
Hamamatsu MPPC S10362-33-100C
60 Co source placed close to fiber
at position A B
SiPM
fiber bundle of 5 LuAG:Ce
MPPC preamplifier (KVI development)
LuAG:Ce
close-up:
fibers coupled to SiPM

contact established with Russian fiber developer
joint activity with WP28 SiPM
laboratory in Chernogolovka

Thanks for your attention

energy resolution - example: NaI:Tl
ΔE/E
(%)
100
40
20
10
4
2
1
2.
35
Nel
R sci
Non prop
4 10 20 40 100 200 400 1000
E / keV
schematic

• identification via
pulse shape analysis PSA
reaction products:
2 AGeV Ar + Ca
charged
events
protons
all events
photons
neutral
events
n

• identification via pulse shape analysis PSA
radius / MeV
visualisation of PSA in polar coordinates
protons
+
photons
angle / °
transformation:
radius
short
2
long
2
,
short
angle a tan( )
long

Ce 3+ luminescence center
5d – 4f energy difference
5d level
5d bands
4f levels
5d bands
4f levels
Ce3+ Pr3+ Nd 3+ Ce3+ Pr3+ Nd 3+
free Ce3+ ion
in crystal
Ce 3+ 5d-4f level distance
in crystal
• 5d level shifts down
• bands
• split by crystal field
• 4f levels hardly affected
the lowest 5d-band edge matters
C. van Eijk

additional candidates
Ce, Pr, Nd 5d-4f transitions - ions in crystal field
5d bands
Ce 3+ Pr 3+ Nd 3+
The lowest
5d-band edge
matters
4f levels
Radioluminescence spectra of 0.5 % Ce 3+ -doped and Pr 3+ -doped
Ca 3(BO 3) 2 single crystals under 241Am 5.5 MeV α-ray.
Y. Fujimoto et al, 2010 IEEE NSS Conf. Rec., pp. 192-194.
Intensity [arb.units]
Wavelength [nm]
X-ray induced emission spectrum of LaF 3:Nd.
C.W.E. van Eijk et al, IEEE Trans. Nucl. Sci., 41, pp. 738-741, 1994.

Ce 3+ energy level shifts
E [eV]
12
10
8
6
4
2
0
free ion
fluorides
chlorides
bromides
iodides
oxides
E gap
Ce 3+ E 5d-4f
sulfides
selenides

comparison of a 1.0 mm and a 0.3 mm fiber
LuAG:Ce
average attenuation coefficient for Ø = 1.0 mm fibers: μ ≈ (1.56 ± 0.32) cm -1
1 mm
Ø
Ø = 1.0 mm fiber
Ø = 0.3 mm fibers: μ ≈ (0.85 ± 0.06) cm -1

improvement of technology
special bundle
LuAG:Ce

improvement of technology
• new Iridium crucible with square nozzle
fiber with quadratic cross section
+ improved packaging
+ cost efficient
830µm
940µm
LYSO:Ce

improvement of technology
LYSO:Ce
• new geometry of the seed:
longer size decreases the longitudinal thermal gradient
• reduced growth speed favors crystallization of monoclinic
crystal structures like LYSO
• operating in oxidizing atmosphere
• better thermal insulation
reduction of macroscopic cracks
quadratic LYSO fiber