Fast inorganic scintillators - status and outlook -

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1 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

2 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

3 Number of dicovered scintillators Quantity of principal inorganic scintillators discovered history 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 investigation of Photomultiplier Curran / Baker 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

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

5 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

6 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 ps fast to slow (afterglow) > ns estimation of achievable light yield: Y E E gap S Q

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

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

9 most scintillators are sensitive to temperature thermal quenching!

10 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!? CsI:Tl 4 LaCl 3 SrI 2 :Eu 2 R stat LaBr 3 but: number of detected photons at 662 kev linear response of the scintillator, index of refraction, light collection, quantum efficiency and linearity of sensor, etc.

11 Energy reslution at FWHM (%) Relative light yield non-proportionality and energy resolution NaI:Tl LaBr 3 :Ce typical examples Energy (kev)

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

13 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

14 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

15 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) p Ba 2+

16 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

17 time-of-flight / ns E (MeV) particle ID: time-of-flight BaF 2 (TAPS) 250 C 0 X AGeV Ca+Ca t (ns) energy / MeV time resolution: s t > 85 ps

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

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

20 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

21 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

22 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 ev 3.46 ev 0.1 fs > ns configuration coordinate 4f levels shielded no line broadening Exc. 6.2 ev Wavelength (nm) 4f 1740 cm -1 broad emission lines C. van Eijk

23 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) f electrons 4f 14

24 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] 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

25 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

26 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 Time (ns)

27 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 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) Lu 2 SiO 5 :Ce 26,000 photons/mev

28 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 E.V.D. van Loef, P. Dorenbos, C.W.E. van Eijk, K. W. Krämer, H.U. Güdel, Energy (kev) Appl. Phys. Lett. 77 (10) (2000) 1467.

29 counts (arb. units) LaBr 3 : 5%Ce 3+ energy resolution Pulse height spectrum 662 kev gamma rays NaI:Tl 61,000 ph/mev 2.8 % FWHM R=2.9% 6.5 % FWHM 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

30 intensity, normalized LaBr 3 :Ce 3+ decay time and time resolution % 5% 10% 20 % 30% 511 kev kev t < 300ps 10-3 decay time 16 ns rise time faster time, ns courtesy Kanai Shah, RMD

31 LaBr 3 :Ce 3+ Counts 345 cm 3 volume BrilLanCe 380 3x3 137 Cs FWHM 3.00% channel

32 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

33 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 , Bi 4 Ge 3 O 12 (BGO) , Lu 2 SiO 5 :Ce (LSO) , Lu 2(1-x) Y 2x SiO 5 :Ce (LYSO) X = , LuAlO 3 :Ce (LuAP) , Lu x Y 1-x AlO 3 :Ce (LuYAP) X = 0.2 LaCl 3 :Ce , (65%) 350 LaBr 3 :Ce , (97%) 380 LuI 3 :Ce , (72%) 472, 535 new generation of dense, bright and radiation hard scintillators

34 counts counts counts Counts PbWO 4 : a fast scintillator - but with low light yield Improved PWO crystal strong temperature quenching t1= 6.5 ns D1= 97% t2= 30.4 ns D2= 3% Cs s/e=14,5% time, ns T = +6 0 C 60Co light yield / a.u. s/e=16.9% T = -7 0 C T = C T = C Na s/e=10.9% light yield / a.u light yield / a.u.

35 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 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 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 ev 3 ev 1 A 1 e ev 3 ev 1 A 1 WO La 1 A 1 MoO ev

36 device crystal modules depth photosensor B where beam energy 10 3 X 0 T TeV CMS ECAL PbWO APD/VPT 4 LHC 7 s E 0.5%@120GeV

37 the PANDA detector at FAIR photon detection with high resolution over a large dynamic range: barrel 10MeV < E < 15GeV high count-rate capability ( ~ 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

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

39 optical transmission light radiation hardness

40 energy resolution s prototype performance extension response to to energies high energy < 50MeV MaxLab optimized light output: PWO-II cooling: operation at T=-25 o C tagged photon 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

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

42 rel. light 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 RT / m -1

43 recovery of radiation damage recovery of normalized light yield / k (420 nm) / m -1 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0, illumination time / min o C Spontaneous LED_1550nm LED_1300nm LED_1060nm LED_940nm LED_464nm illumination time / min 470 nm 525 nm 640 nm 840 nm 935 nm applied integral dose of 60 Co: D = 30Gy

44 technology: micro-pulling-down technique (µpd)

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

46 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 %

47 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

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

49 material density g/cm 3 Z eff emission wavelength nm index of refraction decay time ns light Yield ph/mev LYSO 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

50 LYSO:Ce fiber (Ø = 0.3 mm, L = 100 mm) response to 241 Am - single sided readout LYSO:Ce μ 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

51 LuAG:Ce fibers 100 mm long 1 mm diameter round

52 SiPM readout PET application KVI LuAG:Ce Hamamatsu MPPC S C 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)

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

54 Thanks for your attention

55 energy resolution - example: NaI:Tl N el schematic ΔE/E (%) R sci Non prop E / kev

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

57 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 /

58 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 ion Pr 3+ Ce 3+ Nd 3+ Pr 3+ Nd 3+ in crystal C. van Eijk

59 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 f 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 , 1994.

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

61 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

62 improvement of technology LuAG:Ce special bundle

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

64 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