Ultra High Quantum Efficiency PMT for energy resolution measurements of LaBr 3 (Ce) scintillation crystals

Transcription

1 Ultra High Quantum Efficiency PMT for energy resolution measurements of LaBr 3 (Ce) scintillation crystals Roberto Pani INFN and Sapienza - University of Rome, Italy On behalf of ECORAD Collaboration Cinti M.N., Pellegrini R., Bennati P., Ridolfi S., Mattioli M., Scafè R., Pisacane F., Baldazzi G., Navarria F., Lo Meo S., Moschini G., Orsolini Cancelli V.

2 New generation UBA photocathode PMT can strongly improve spectrometric and imaging performances of scintillation detectors Hamamatsu R76-2 Ultra BiAlkaly Hamamatsu Flat Panel H85 Position sensitive PMT 1 inch 1 inch 15 mm 5 mm QE max. = nm Number of dinode = 1 Gain= HV= -9 V Metal Channel dynode Metal channel dynode QE typ. = nm Number of dinodes = 12 Gain = 1. 1 HV= -1 V 8 x 8 anode array mm pitch

3 Hamamatsu PMT investigated PMT ext. Size Photocatode material 38 nm typ.(%) Gain typ. Dynode Structure / stage Voltage divider Ultra Bialkali Metal Channel R76U mm 2 UBA 42 % / 1 Tapered/ No tapered R76U mm 2 Bialkali BA 22 % Metal Channel / 1 Tapered/ No tapered R mm Bialkali BA 3 % Linear Focused / 8 Tapered H85 Flat Panel (position sensitive) 49 x 49 mm 2 Bialkali BA 27 % Metal Channel / 12 No tapered

4 Scintillation Crystals for SPET and PET Density (g/cm 3 ) Z eff. Light yield (ph/mev) Decay time (ns) Refr. index ΔE/E (PMT) λ Emiss max (nm) NaI(Tl) , CsI(Tl) , YAP , LaCl 3 (Ce) , 1.9 (65%) 4 LaBr 3 (Ce) , 16 7 kev 1.9 (97%) 4 kev LuI 3 (Ce) , BGO , kev 48 LSO , kev 42 LYSO , kev 42

5 Intrinsic Scintillator Energy Resolution Crystal ER 662 kev ER scint (%) ER st (%) ER noise (%) Light detector Ref. LaBr 3 (Ce) SDD Fiorini (26) LaBr 3 (Ce) YAP CsI(Tl) BGO R6231 MOD SN Hamamatsu APD Adv.Phot.Inc. PMT XP2254B Philips PMT XP2Y Photonis Moszynski (27) Moszynski (2) Allier (1998) Moszynski (26) NaI(Tl) PMT typical LSO W.Moses, NIM A, 487 (22) Luminosity 662keV - PMT 25% QE) Relative Light Yield PMT XP2Y Photonis Moszynski (26) Light Non Proportionality A Prescott and Narayan, NIM A, 75 (1969) B G.Bizarri, IEEE TNS, Vol 53,2 (26) NaI(Tl) A LaBr 3 (Ce) B

6 LaBr 3 (Ce) / PMT Pulse height non linearity Co 6 gamma ray pulse HV = -7 V Decay Time (ns) Light yield (ph/mev) NaI(Tl) 23 41, HV = -5 V LaBr 3 (Ce) 16 63, LaBr 3 (Ce) produces dynode current ten times more than NaI(Tl) Gamma Ray Spectroscopy With a Ø 19 x19 mm 3 LaBr3 : :5% Ce3+ Scintillator P. Dorenbos, J. T. M. de Haas, and C. W. E. van Eijk, Member, IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 51, NO. 3, JUNE 24

7 PMT Pulse linearity PMT tapered voltage divider R76 Pulse linearity Deviation (%) 4% 2% % -2% R76U-2 UBA Tapered No Tapered -4% Courtesy of Hamamatsu Photonics K.K. LaBr 3 (Ce) 12.5mm x 12.5 mm Deviation (%) 4% 2% % -2% R76-2 R76U R6231 Tapered PMT -4% 2 4 6

8 LaBr 3 (Ce) light emission well matches UBA photocathode response Hamamatsu R76-2 Ultra BiAlkaly 1 inch 1 inch QE max. = nm Number of dinode = 1 Gain= HV= -9 V Metal Channel dynode Quantum Efficiency (%) 5% 4% 3% 2% 1% UBA Photocathode response R76U-2 UBA R76U - BA LaBr3(Ce) NaI(Tl) LYSO % Wavelenght (nm) 6 7 Courtesy of Hamamatsu Photonics K.K.

9 Energy Resolution 1.1 R6231 Hamamatsu - Standard PMT LaBr 3 (Ce) Energy resolution 12.5mm x 12.5 mm diam. Moszynski,27a NaI(Tl) Poisson contributionb a M. Moszyński, et al, Study of LaBr3 Crystals Coupled to Photomultipliers and Avalanche Photodiodes, 27 IEEE Nuclear Science Symposium Conference Record b 21 ± 66 phe/mev a

10 Counts (a.u.) Counts (a.u.) LaBr 3 (Ce) 12.5mm x 12.5 mm R6231 Standard PMT ER = (7.7±.1)% NaI(Tl) R6231 ER=(9.2 ±.1)% Co 57 source kev Counts (a.u.) Counts (a.u.) R76U-2 UBA ER=(8. ±.1)% R76U BA ER=(1.1 ±.1)%

11 LaBr 3 (Ce) 12.5mm x 12.5 mm UBA R76-2 PMT 32 kev 81 kev Counts Pulse height distribution counts kev 81 kev 274 kev NaI(Tl) 274/32 kev 32 kev /38 kev Ba kev 38 kev 6 4 ER=(2.7 ±.1)% 1332 kev Energy (KeV) 4 Na 22 ER=(4. ±.1)% 511 kev 2 Counts Energy (KeV) 4 Counts 2 Co 6 Cs kev 1274 kev ER=(3.6 ±.1)% Energy (KeV)

12 Energy Resolution 1% 1% 1% UBA PMT Energy resolution LaBr 3 (Ce) scintillation crystal- Tapered PMTs R76-2 UBA R76U - BA R

13 UBA energy resolution improvement LaBr 3 (Ce) scintillation crystal kev BA UBA Improvement UBA/BA % 1. % 22% % 8. % 19% % 4. % 23% % 3.6 % 2% % 2.7% 22% Improvement (Mean Value) 21%

14 Energy Resolution Theory R ( E) = R 2 + s Nηα δ 1 δ Intrinsic Scintillation Contribution Non homogeneities Light non proportionality Statistical generation of the signal N: number of photons in a scintillation flash α: Collection efficiency of phe by the first dinode δ: dynode moltiplication factor η: Quantum Efficiency

15 High QE improvement Expected energy resolution improvement QE QE UBA BA = 1.91 = 1.38 kev a ER sci LaBr 3 (Ce) ER stat. Improvement UBA/BA ER = ER ER 2 2 stat. sci 81 6.% % % % 1.38 a M. Moszyński, Ł. Świderski, T. Szczęśniak, A. Nassalski, A. Syntfeld-Każuch, W. Czarnacki, G. Pausch, J. Stein, P. Lavoute, F. Lherbert, F. Kniest, Study of LaBr3 Crystals Coupled to Photomultipliers and Avalanche Photodiodes, 27 IEEE Nuclear Science Symposium Conference Record,N24-172,

16 Quantum Efficiency (%) H85 - UBA 36%@ 38 nm 3% 2% 1% High QE and spatial resolution Ultra Bialkaly (UBA) Multi Anode PMT - H85 Courtesy of Hamamatsu Photonics K.K. 4% H85 UBA H85 BA LaBr3(Ce) NaI(Tl) LYSO % Wavelenght (nm) BA Hamamatsu Flat Panel H85 Position sensitive PMT 15 mm 5 mm Metal channel dynode QE typ. = nm Number of dinodes = 12 Gain = 1. 1 HV= -1 V 8x8 anode array mm pitch

17 Intrinsic Spatial Resolution LaBr 3 (Ce) continuous crystal 49x49x5 mm 3 integral assembled BA MA-PMT H mm I.S.R. (CFoV) = 1.5 mm I.S.R. (Best) =.9 mm Counts Position (mm).4 mm Φ collimated Tc 99m source 1.5 mm step scanning

18 Intrinsic Spatial Resolution LaBr 3 (Ce) continuous crystal 49x49x5 mm 3 integral assembled BA MA-PMT H85 1 mm Φ collimated Ba 133 source 1.5 mm step scanning 5mm Overall SR = 1.5 mm 8 kev 5mm Overall SR = 1.25 mm 356 kev ISR min =.83mm 8 ISR avg =1.14mm ISR min =.48mm 12 1 ISR avg =.7mm 6 8 counts 4 counts image pixels image pixels

19 Ultra BiAlkaly Multi Anode PMT H85 Expected results LaBr3(Ce) continuous crystal 49x49x5 mm3 integral assembled Energy Resolution kev H85 H85 BA UBA % 1.5% % 8.4% % 4.% % 3.6% Intrinsic Spatial Resolution kev H85 BA H85 UBA mm 2. mm mm 1.25 mm mm.95 mm mm.9 mm mm.65 mm Improvement 1%

20 Conclusion New generation UBA photocathode has strongly improved PMT Quantum efficiency (42% at 38 nm). LaBr 3 (Ce) light emission well matches UBA photocathode response. Intrinsic energy resolution of scintillators seriously limits the expected energy resolution improvement (only 2% for LaBr 3 (Ce)). UBA photocathode PMT (metal channel dynodes) shows similar energy resolution values of standard PMT (3% QE). In gamma imaging, spatial and energy resolution improvement is expected from LaBr 3 (Ce) crystal coupled to MA-PMT based on metal channel dynodes.

21 Energy resolution R76-2 UBA % UBA No UBA Energy Resolution (%) 1% E.R. 1% LSO kev LSO YAP UBA / BA UBA / BA / / / / 18.3 % UBA NoUBA / / / 8.5-1% E.R. 1% YAP / keV 21% 19%