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× Development of an 8 × 8 array of Development of an 8 8 array of LaBr 3 (Ce) scintillator pixels for LaBr 3 (Ce) scintillator pixels for a gaseous Compton a gaseous Compton gamma- -ray camera ray camera gamma TIPP09 @ Epocal Tsukuba, Tsukuba, Japan. (2009.3.14) Shunsuke KUROSAWA K. Hattori, C. Ida, S. Iwaki, S. Kabuki, H. Kubo, K. Miuchi, H. Nishimura, J. Parker, A. Takada, M. Takahashi, T. Tanimori, K. Ueno, Y. Yanagida A Dept. of Physics, Graduate school of Science, Kyoto University, Kyoto, Japan A World Engineering System, Kyoto, Japan

Contents • Introduction – Compton gamma-ray Camera • LaBr 3 (Ce) array – Property of LaBr 3 (Ce) – Measurement of a monolithic LaBr 3 (Ce) – Measurement of a LaBr 3 (Ce) array • Compton Camera with LaBr 3 arrays – Gaseous TPC – Imaging with the camera • Summary

Compton gamma camera Camera is used for astronomy (Ueno’s poster id=17), and medical imaging (Kabuki’s talk id=30). gaseous TPC (time projection chamber) ： TPC [containing μ -PIC(MPGD), α GEM] 10cm --- energy and 3-D track of Compton-recoil electron Scintillation camera ： [Pixel array Scintillator] (Prototype: GSO array) μ -PIC --- energy and position of scattered gamma ray GEM Scintillator � Large FOV (~3str) Reconstruct incident � Kinematical background rejection by comparison of two α gamma ray event by event angles

To obtain a higher angular resolution Angular resolution of the Compton camera depends on the energy resolution of scintillator m e c 2 K cos φ ＝ 1 － 49mm ( E + K ) E 8 × 8 GSO Incident γ array level Angular resolution (FWHM) [degree] Δ φ Angular resolution (ARM) Sci. Eng. Res. Com. Angular @662keV Res. @662keV 4.2 ° 10.5 % Scattering 3.1 ° 7% angle φ 2.3 ° 5% Recoil e - α 2.1 ° Scattered γ 3% K : energy E : energy Calculated assuming 1, no error in position of Compton point 2, energy Res. of TPC Doppler broadening (Ar) : 30 % @ 22 keV Zoglauer et al. (2003)

Property of scintillators Density Decay time Light output Hydroscopic Radiation （ g/cm 3 ） constant Hardness (Relative) （ ns ） NaI(Tl) 3.67 230 100 Strong very weak CsI(Tl) 4.53 1050 85 Weak very weak BGO 7.13 300 7-12 No weak LSO 7.4 40 40-75 No strong YSO 4.45 40 30-45 No strong PWO 8.2 ~3/<40 26/4 No strong GSO(Ce) 6.71 30~60 18 No strong LaBr 3 (Ce) 5.3 20 160 strong strong

LaBr 3 (Ce) scintillator Quantum Efficiency � Excellent energy resolution 30 100 (Q. E.) : ~3% @ 662keV (FWHM) PMT bi-alkali 90 : ~1.5% @ 2615keV (FWHM) 25 � High light yield 80 : 160 NaI% @ Ce 5%mol 70 [ cf. GSO(Ce) : 20 20 NaI% ] Counts (a. u.) 60 temp. dependency: 0.01%/deg. Q. E. [%] � Fast decay time 15 50 Emission : ~ 20 nsec @ Ce 5%mol spectrum 40 temp. dependency: 0.04 nsec/deg. LaBr 3 10 � Radiation hardness 30 pulse height: 20 drop ~ 8% (1kGy 60 Co) 5 � Internal radioactivity 10 rate < 5 Hz /cc (30 – 3000 keV) 0 0 � Hygroscopic 300 350 400 450 500 wave length [nm] spectrum : Shah et al. (2003) Loef et al., (2000), Drozdowski et al. (2007) Q. E. : Hamamatsu catalog M. Moszy ń sk et al. (2006)

LaBr 3 (Ce) scintillator Saint-Gobain BrilLanCe380 Energy resolution measured with a single- Size: φ 38 × 38mm 3 anode PMT (SAPMT) (HPK R6231) 133 Ba GSO E -0.501 ± 0.002 4.1 ± 0.1 % LaBr 3 @ 356 keV 3.3 ± 0.1 % @ 662 keV

Irradiation points Uniformity 18mm 8 0mm Collimator 10mm φ =2mm 133 Ba 9mm 25mm Source LaBr 3 35mm PMT side @ 356 keV peak [ch] Top view side view ± 1% (normalized) Ave. ± σ ADC value 1.005 ± 0.002 Light output uniformity (FWHM) @ 356 keV Energy resolution Energy resolution uniformity ± 0.2% point Ave. ± σ 4.11 ± 0.05 %

Naked LaBr 3 pixel Test of our cutting & polishing technique Size: 6 × 5 × 14mm 3 pixel Saint-Gobain BrilLanCe380 glass window : none Size: φ 38 × 38mm 3 Hermetic package : none 133 Ba Put the crystal on 133 Ba single anode PMT (R6231) directly under the dry condition Energy resolution (FWHM) 4.5 ± 0.1% @ 356 keV 3.5 ± 0.1% @ 662 keV

Assembly of LaBr 3 (Ce) array Using our technique, we cut 5.8 × 5.8 × 15.0mm 3 pixels out of two φ 38 × 38 mm 3 LaBr 3 crystals and assembled an 8 × 8 array. 6.1 mm pitch Saint-Gobain 54mm BrilLanCe380 Size: φ 38 × 38mm 3 20mm 1/2 attenuation length Effective area : 49 × 49 mm 2 @662keV (=PMT photocathode) LaBr 3 (Ce): 18 mm Glass window : Quartz (t 2.3 mm) Hermetic package : Aluminum ( t 0.5 mm )

Performance of each pixel To estimate the performance without the effect of gain uniformity ( ∼ 3) among 64 anodes of Multi-Anode PMT (H8500) Energy resolution (FWHM) [%] irradiation of collimated gamma rays to a pixel one by one collimator φ 2mm lead bricks 7cm length 133 Ba source Map of energy Res. of 8 × 8 pixels Single-anode PMT LaBr 3 array HPK R6236 Energy resolution (FWHM) (2-inch square ) @ 356 keV Ave. ± σ = 5.5 ± 0.7 %

Readout with H8500 LaBr 3 array MAPMT HPK H8500 Resister 5 4 52mm m chain m H8500 Anode size: 6.08mm × 6.08mm Number of Anode: 8 × 8 Photocathode: Bialkali Window: Borosilicate (thickness:1.5mm) HV: ~-800V

Readout of an array camera Charge-division 4ch readout with a resister chain method a c + − − 64 anodes c d a b = x of PMT + + + a b c d + − − a c b d = y + + + 4 ch output a b c d (a, b, c, d) X, Y position d b R=100 Ω Sum y anode pre.AMP = + + + E a b c d x Energy

Image and energy spectrum � Flood field irradiation image 137 Cs φ 38 × 38mm 3 � Energy spectrum 8x8 pixel monolithic ( 133 Ba) crystal array (sum of all pixels) Energy resolution of Array, (FWHM) 7.6 ± 0.4% @ 356 keV 5.7 ± 0.1% @ 662 keV

Energy resolution (FWHM) of each pixel @ 662 keV ( 137 Cs) Using MAPMT H8500 (FWHM) @ 662 keV [%] Energy Resolution Ave. ± σ : 5.8 ± 0.9% cf. GSO array 10.8 ± 1.0%

Energy resolution vs. energy array φ 38 × 38mm 3 monolithic crystal array: FWHM(%)=(5.7 ± 0.4) × (E/662keV) - 0.52 ± 0.01

15mm-thickness array LaBr 3 arrays Energy resolution (FWHM) [%] @ 662 keV (1) (2) Energy Resolution (3) (4) (FWHM) @ 662keV (1) 5.8 ± 0.9 % (2) 6.4 ± 1.2 % (3) 6.0 ± 0.8 % (4) 5.8 ± 0.8 % 20mm-thickness array (pixel size: 5.8 × 5.8 × 20.0mm 3 ) (5) 5.5 ± 0.8 % (5)

Gaseous TPC 3-D electron Size ： 10 × 10 × 10 cm 3 Drift cage tracking Gas : Ar+C 2 H 6 1atm GEM Drift ： FPGA 100MHz clock μ -PIC Gain: ~30,000 (GEM gain : ~10) Position Resolution (FWHM) ： 10cm drift direction ~ 0.6 mm 10cm horizontal plane ~ 0.4 mm 500keV μ -PIC (micro pixel chamber) 400μm pitch � 2-D gaseous detector � Size: 10 cm x 10 cm ~ 65,000 pixels � Gas gain: < ~6,000 (stable driving 10cm anode cathode more than 1 month)

Setup of a Compton camera LaBr 3 TPC source e - γ γ 2m 50mm 200mm Source Gaseous TPC Reconstruction of a Compton event γ γ 4 LaBr 3 Electron arrays e - 3-D track e - γ γ 110mm

Angular resolution Measured by point sources With GSO array Angular resolution Angular resolution (FWHM) [degree] (FWHM) @662 keV 4.2 ± 0.3 ° (LaBr 3 ) 6.4 ± 0.2 ° (GSO) With LaBr 3 array

Performance of a Compton camera LaBr 3 TPC source Source 131 I (364keV) e - 3cm γ γ 3cm cube 50mm 200mm LaBr 3 with GSO array with LaBr 3 array

summary • In order to improve the angular resolution of Compton Camera, we assembled an 8 × 8 LaBr 3 pixel array. – Pixel size : 5.8 × 5.8 × 15 mm 3 – Pixel pitch: 6.1mm (the same as that of MAPMT H8500) – Package size : 54 × 54 × 20 mm 3 • Dynamic range: 80 – 1000 keV • Energy resolution of the array with MAPMT （ FWHM 、 @662keV ） 5.8 ± 0.9 % – LaBr 3 array 10.8 ± – GSO array 1.0 % • Angular resolution of gamma camera (FWHM, @ 662 keV) 4.2 ± 0.3 deg. – With LaBr 3 array 6.4 ± 0.2 deg. – With GSO array • Future work – LaBr 3 array: Individual readout system for each anode channel. – TPC: Improve accuracy of electron tracking (cf. Hattori’s poster id=85)

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