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
basic concept of a scintillation detector X rays gamma rays heavy charged particles thermal neutrons Photoelectric effect Compton effect Pair production Bethe Bloch e scintillator nuclear reaction ionization excitation many e-h pairs energetic neutrons proton request for a wide spectrum of detector materials
Number of dicovered scintillators Quantity of principal inorganic scintillators discovered history 4 3.5 3 2.5 2 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 1.5 1 0.5 0 investigation of Photomultiplier Curran / Baker 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 M.Korzhik, 2003 X-ray imaging screens a -scattering Years year Alcali-Halides Oxides 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
pulse height / mv inorganic scintillators large variations in: compactness luminescence yield time / ns volume: 1X 0 3
basic processes basic processes in inorganic scintillator ionic crystal host material E gap > ~ 4-12 ev e luminescence center luminescence centre intrinsic or dopant conduction band luminescence h valence band thermalization transport
but it is more complex! e thermally released conduction band Trap radiationless recombination Shallow trap Defect direct excitation relaxation luminescence LC h thermalization transfer or luminescence valence band thermalization 1-100 ps fast to slow (afterglow) > ns estimation of achievable light yield: Y E E 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!
YAlO 3 :Ce resolution at 662 kev / % Lu 3 Al 4 O 12 :Pr NaI:Tl BaF 2 BGO LSO:Ce achievable energy resolution not only determined by photon statistics!? 10 8 6 CsI:Tl 4 LaCl 3 SrI 2 :Eu 2 R stat LaBr 3 but: 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.
Energy reslution at FWHM (%) Relative light yield non-proportionality and energy resolution 1.2 1.1 NaI:Tl 1.0 0.9 LaBr 3 :Ce typical examples 10 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
BaF 2 both luminescence components show a different temperature dependence different scintillation mechanisms fast slow component slow component: strongly temperature dependent determines energy resolution dy/dt-1.4%/ 0 K
BaF 2 : fast UV luminescence CondB 6s, 5d Ba 2+ E gap STE ValB 2p F - Ionic crystal E VOC < E gap E VOC fast Core-Valence Luminescence CVL Auger-free luminescence Cross luminescence OCoreB Yu.M. Aleksandrov et al, Sov. Phys. Sol. State 26 (1984) 1734 5p Ba 2+
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 time photon E-fast photons protons fast component total light output signal integration width E-total plastic VETO BaF 2 -detector identification of charged and neutral events
time-of-flight / ns E (MeV) particle ID: time-of-flight BaF 2 (TAPS) 250 C 0 X... 200 2 AGeV Ca+Ca 150 100 50 0 0 2 4 6 8 10 t (ns) energy / MeV 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 complete new readout invariant mass / MeV
CVL candidates E gap 4-13 ev Condition for CVL E VOC < E gap I Br Cl F E VOC 13 ev 17 ev Sr 2+ Ca 2+ P.A. Rodnyi, Sov. Phys. Solid State 34(1992)1053 C.W.E. van Eijk, Nucl. Tracks. Radiat. Meas. 21(1993)5 8 ev 10 ev 7.5 ev 4.5 ev Ba 2+ K + CVL Cs + Rb + F, Cl, Br, I CondB ValB OCoreB decay time ~ 1 ns light yield 2000 photons/mev
Ce 3+ luminescence center e Ce 3+ conduction band Core + 1 electron in 4f state excitation h relaxation 5d 4f emission valence band 5d 4f allowed dipole transition fast response ~ 20 ns
Ce 3+ luminescence center energy Intensity (arb. units) Ce 3+ relaxation Stokes shift 1 ps quenching Rodnyi C 3h 5.10 ev 4.96 ev 4.71 ev 4.52 ev 4.41 ev 5d LaCl 3 :0.57%Ce S=5900 cm -1 3.68 ev 3.46 ev 0.1 fs > ns configuration coordinate 4f levels shielded no line broadening Exc. 6.2 ev 150 200 250 300 350 400 450 Wavelength (nm) 4f 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 see papers by P. Dorenbos Ce 3+ Egap 5d 4f in favourable host Y E E gap LY ~ 20 ns S Q Ce 3+ levels and Egap E [ev] 12 10 fluorides chlorides E gap Ce 3+ E 5d-4f oxides 8 bromides free ion iodides 6 sulfides 4 Egap l matching light sensor 2 0 selenides timing properties: 1 n l 2 2 n 2 5d 4f 3 3 2
K 2 LaX 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+ Intensity (a.u.) scintillation decay 25 ns 10% LaCl3 :Ce 3+ NaI:Tl 230 ns 30% LSO NaI:Tl Lu 2 SiO 5 :Ce 40 ns 0 200 400 600 800 1000 Time (ns)
LaCl 3 :Ce 3+ Intensity (a.u.) energy resolution 55 Fe R=42% 241 Am R=10.5% 137 Cs R=3.3% 50,000 photons/mev NaI:Tl 40,000 photons/mev 0 5 10 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 100 500 800 Lu 2 SiO 5 :Ce 26,000 photons/mev
LaCl 3 :Ce 3+ Counts 4 x 6 E/E=4.1% 4 x 6 mm 2 32keV Ba E/E=3.1% La X-ray escape peak 400 500 600 700 800 E.V.D. van Loef, P. Dorenbos, C.W.E. van Eijk, K. W. Krämer, H.U. Güdel, 0 200 400 600 800 Energy (kev) Appl. Phys. Lett. 77 (10) (2000) 1467.
counts (arb. units) LaBr 3 : 5%Ce 3+ energy resolution 1.2 1.0 0.8 0.6 0.4 0.2 Pulse height spectrum 662 kev gamma rays NaI:Tl 61,000 ph/mev 2.8 % FWHM R=2.9% 6.5 % FWHM 0.0 0 100 200 300 400 500 600 700 800 energy (kev) light yield 70,000 photons/mev (NaI:Tl 40,000 ph/mev) decay time 16 ns (NaI:Tl 230 ns) 380 E.V.D. van Loef, P. Dorenbos, C.W.E. van Eijk, K.W. Krämer, H.U. Güdel Appl Phys Lett 79(2001)1573
intensity, normalized LaBr 3 :Ce 3+ decay time and time resolution 10 0 10-1 10-2 0.5% 5% 10% 20 % 30% 511 kev - 511 kev t < 300ps 10-3 decay time 16 ns rise time faster 0 50 100 150 200 250 time, ns courtesy Kanai Shah, RMD
LaBr 3 :Ce 3+ Counts 345 cm 3 volume 6000 5000 BrilLanCe 380 3x3 137 Cs 4000 3000 2000 FWHM 3.00% 1000 380 0 0 200 400 600 800 1000 channel
Lanthanum halides: X-ray excited optical luminescence LaCl 3 :Ce 3+ LaBr 3 :Ce 3+ Ce concentration, light yield Ce concentration, light yield Ce concentration, host emission
some scintillator specs Density g/cm 3 Attenuation length at 511 kev mm Photoel effect % Light yield phot/mev Decay time ns Emission max nm NaI:Tl 3.67 29.1 17 41,000 230 410 Bi 4 Ge 3 O 12 (BGO) 7.1 10.4 40 9,000 300 480 Lu 2 SiO 5 :Ce (LSO) 7.4 11.4 32 26,000 40 420 Lu 2(1-x) Y 2x SiO 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 x Y 1-x AlO 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
counts counts counts Counts PbWO 4 : a fast scintillator - but with low light yield Improved PWO crystal 100000 strong temperature quenching 10000 1000 t1= 6.5 ns D1= 97% t2= 30.4 ns D2= 3% 3000 2500 137 Cs 100 10 2000 1500 s/e=14,5% 1 0 100 200 300 400 500 600 700 800 900 time, ns 1000 500 10000 8000 T = +6 0 C 60Co 0 3000 200 400 600 800 1000 light yield / a.u. s/e=16.9% 6000 4000 2000 T = -7 0 C T = -22 0 C T = -30 0 C 2000 1000 22 Na s/e=10.9% 0 100 200 300 400 500 600 700 800 light yield / a.u. 0 200 400 600 800 1000 light yield / a.u.
E, cm -1 PbWO 4 : a fast scintillator - but with low light yield WO 4 2- Energy levels of dopings pure PbWO 4 3T 3 1, T 2 3.9 ev 3 ev Donor Acceptor non radiative losses in PWO temperature quenching of WO 4 2- luminescence 1 A 1 R 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 WO 4 2-3.9 ev 3 ev 1 A 1 e - 0.2 ev 3 ev 1 A 1 WO 4 3- +La 1 A 1 MoO 4 3-2.5 ev
device crystal modules depth photosensor B where beam energy 10 3 X 0 T TeV CMS ECAL PbWO 4 82 26 APD/VPT 4 LHC 7 s E 0.5%@120GeV
the PANDA detector at FAIR photon detection with high resolution over a large dynamic range: barrel 10MeV < E < 15GeV high count-rate capability (2 10 7 ~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
energy resolution s prototype performance extension response to to energies high energy < 50MeV photons @ MaxLab optimized light output: PWO-II cooling: operation at T=-25 o C tagged photon facility @ MAMI, Mainz E = 26 MeV E =43.3MeV readout with photomultiplier e - s 64 MeV < E 1.5 GeV readout with incident energy / GeV photomultiplier
readout via SADC: further improvement energy-resolution ( 3x3 matrix ) 1 ns time resolution
rel. light loss @ 25 o C / % 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 k @ RT / m -1
recovery of radiation damage recovery of normalized light yield / % @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 100 90 80 70 60 50 @T= -25 o C Spontaneous LED_1550nm LED_1300nm LED_1060nm LED_940nm LED_464nm 0 200 400 600 800 1000 1200 1400 1600 illumination time / min 470 nm 525 nm 640 nm 840 nm 935 nm applied integral dose of 60 Co: D = 30Gy
technology: micro-pulling-down technique (µpd)
material LuAG :Ce density g/cm 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 Lu 3 Al 5 O 12 :Ce 3+ tested fibers: 0.45mm - 2.0mm emission spectra at various positions: slight changes
LuAG:Ce response to 241 Am - single sided readout Ø 1.0 mm fiber ~ e -μ d additional wrapping with teflon increases the light yield by 70 %
response to 241 Am - coincidence readout fiberlength between 2.5 cm and 4.5 cm LuAG:Ce time resolution of a single PMT: (deduced from left - right coincidence) σ t Δt 2
improvement of technology efficiency reproducibility multi-pulling packaging 100 mm LuAG:Ce simultaneous growth of 7 LuAG fibers 20 fibers of comparable quality
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 2x SiO 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 LYSO:Ce μ 0.018 cm -1 μ 0.68 cm -1 average attenuation coefficient: μ (0.68 ± 0.02) cm -1 LuAG:Ce (Ø 0.3 mm): μ (0.85 ± 0.06) cm -1 good homogeneity of all investigated fibers
LuAG:Ce fibers 100 mm long 1 mm diameter round
SiPM readout PET application KVI LuAG:Ce Hamamatsu MPPC S10362-33-100C 60 Co source placed close to fiber at position A B close-up: fibers coupled to SiPM SiPM fiber bundle of 5 LuAG:Ce MPPC preamplifier (KVI development)
contact established with Russian fiber developer joint activity with WP28 SiPM laboratory in Chernogolovka
Thanks for your attention
energy resolution - example: NaI:Tl 100 40 2.35 N el schematic ΔE/E (%) 20 10 4 2 R sci Non prop 1 4 10 20 40 100 200 400 1000 E / kev
identification via pulse shape analysis PSA all events reaction products: 2 AGeV Ar + Ca charged events protons photons neutral events n
identification via pulse shape analysis PSA radius / MeV visualisation of PSA in polar coordinates transformation: radius short 2 long 2, angle short a tan( ) long protons + photons angle /
Ce 3+ luminescence center 5d 4f energy difference 5d level Ce 3+ 5d-4f level distance 5d bands 5d bands in crystal 5d level shifts down bands split by crystal field 4f levels hardly affected the lowest 5d-band edge matters 4f levels 4f levels free Ce Ce 3+ 3+ ion Pr 3+ Ce 3+ Nd 3+ Pr 3+ Nd 3+ in crystal C. van Eijk
additional candidates Intensity [arb.units] Ce, Pr, Nd 5d-4f transitions - ions in crystal field 5d bands The lowest 5d-band edge matters 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. 4f levels Ce 3+ Pr 3+ Nd 3+ 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 fluorides E gap Ce 3+ E 5d-4f 10 8 6 4 free ion chlorides oxides bromides iodides sulfides 2 0 selenides
comparison of a 1.0 mm and a 0.3 mm fiber LuAG:Ce Ø Ø = 1.0 mm fiber average attenuation coefficient for Ø = 1.0 mm fibers: μ (1.56 ± 0.32) cm -1 Ø = 0.3 mm fibers: μ (0.85 ± 0.06) cm -1 1 mm
improvement of technology LuAG:Ce special bundle
improvement of technology LYSO:Ce new Iridium crucible with square nozzle 830µm 940µm fiber with quadratic cross section + improved packaging + cost efficient
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