Development of a Gamma Camera Based on an

Development of a Gamma Camera Based on an 8 8 Array of La. Br 3(Ce) Scintillator Pixels Coupled to a 64 -channel Multi-anode PMT Hidetoshi Kubo, K. Hattori, S. Kabuki, S. Kurosawa, K. Miuchi, T. Nagayoshi, H. Nishimura, Y. Okada, R. Orito, A. Takada, T. Tanimori, K. Tsuchiya, K. Ueno Kyoto University, Waseda University, Kobe University, Japan IEEE 2007 NM 1 -1

Outline Scintillation camera in Compton camera n Performance of monolithic La. Br 3 n Assembly of La. Br 3 pixel array n Performance of La. Br 3 pixel array n Compton camera using La. Br 3 pixel array n Summary n

Our Compton Gamma-Ray Camera Ø Gaseous TPC 0. 1 a few 10 Me. V -ray 3 D track and energy of recoil electron Ø Scintillation camera (MPGD) MP 4 -1 Tanimori, N 33 -5 Ueno position and energy of scattered -ray Better energy resolution of scintillator E Better angular resolution of Compton camera La. Br 3 (Ce) has the best energy resolution of all known scintillators.

2006 IEEE NSS Kubo et al. , Coupled with optical grease GSO Scintillation Camera 64 ch MAPMT(HPK Flat-panel H 8500) l 8 8 52 mm anodes lanode pitch: 6. 1 mm l 12 stage metal channel dynode l. Size: 52 mm (Photocathode coverage ~89%) l. Anode uniformity: min: max~1: 3 PSA (Pixel Scintillator Array) l. GSO 50 mm Scintillation camera (Ce) crystal (Hitachi Chemical) no hygroscopic: it is easy to assemble radiation hard l 8 8 pixels l. Pixel size: 6 mm 13 mm fits the anode-pitch of H 8500 l. Pixels are optically isolated with the 3 M ESR film (65 mm thick) 6 6 PMTs 33 33 cm 2 2000 GSO pixels

Applications of Compton camera • Me. V gamma-ray Astronomy • Medical Imaging GSO Scintillation camera 1. 4 m Balloon experiment was conducted in 2006 N 59 -8 Takada thyroid gland phantom 131 I injection 364 ke. V M 18 -110 Kabuki, M 13 -141 Kohara, M 18 -150 Shirahata

La. Br 3(Ce) scintillator • High light yield (Na. I%) 160% E. V. D. van Loef, et al. , (2000) cf. GSO(Ce) 20% Saint-Gobain • Fast decay time: 26 nsec Bril. Lan. Ce 380 • hygroscopic Size: 38 38 mm 3 it is difficult to assemble Energy resolution measured with a single-anode PMT(HPK R 6231) FWHM(%)=(3. 1 0. 3) (E/662 ke. V)-0. 53 0. 02

Assembly of La. Br 3 pixel array 8 8 array (=PMT photocathode) 54 mm Crystal/package m La. Br 3 (Saint-Gobain Bril. Lan. Ce 380) Size: 38 38 mm 3 49 mm 54 m 6. 1 mm pitch PMT package: 52 52 mm 2 Area ratio: (5. 8 8/54)2 =74% 20 mm Hermetic package Glass window(2. 3 mm t) of aluminum(0. 5 mm t) We quarried two 38 38 mm 3 La. Br 3 crystals to 5. 8 x 15. 0 mm 3 pixels and assembled an 8 8 array with a pitch of 6. 1 mm (=anode pitch of H 8500 PMT) by our technique. The crystal with an area of 49 49 mm 2 is sealed in a compact aluminum package with glass window.

Energy resolution of La. Br 3 pixel array coupled to single-anode PMT To remove the effect of gain-uniformity ( 3) among 64 anodes of MAPMT(H 8500) 2 inch square Energy resolution (FWHM) single-anode PMT of 64 pixels: (HPK R 6236) 5. 8 0. 9% at 356 ke. V collimated gamma rays 4. 9 0. 7% at 662 ke. V were irradiated to one pixel

Readout of a 64 ch Multi-anode PMT La. Br 3 array 64 ch MAPMT HPK Flat-panel H 8500 Resistor chain board • Each anode is connected to resistors, and 4 ch at the corners in resistor chains are read. 100 • X, Y positions of 64 anodes are obtained in the charge-division method.

Flood field irradiation image 57 Co 122 ke. V 137 Cs 662 ke. V

Light output uniformity La. Br 3 8 x 8 pixel array Average : 71. 3 RMS : 14. 5 RMS/Av. =20% corrected with PMT-anode gain Maximum value is normalized to 100.

Energy spectrum of La. Br 3 pixel array 133 Ba 38 38 mm 3 monolithic crystal 137 Cs 22 Na 8 x 8 pixel array

Energy resolution La. Br 3 8 x 8 pixel array FWHM(%)=(6. 2 0. 4) 137 Cs 662 ke. V (E/662 ke. V)-0. 63 0. 01 worse than the 38 38 mm 3 monolithic crystal by factor 2 8 8 pixel array Average 6. 3% RMS 1. 2% 38 38 mm 3 crystal

GSO array vs. La. Br 3 array Energy resolution GSO 6 6 13 mm 3 8 x 8 array: FWHM(%)=(10. 4 0. 3) (E/662 ke. V)-0. 51 0. 01 better by factor 1. 7 La. Br 3 array: FWHM(%)=(6. 2 0. 4) (E/662 ke. V)-0. 63 0. 01

Compton camera using La. Br 3 pixel array M 18 -110 Kabuki 10 x 10 cm 3 Gaseous TPC Angular resolution (FWHM) [deg] La. Br 3 pixel array GSO La. Br 3 Improved by 2 4. 0 deg at 662 ke. V Energy [ke. V] Cube phantom with 131 I (364 ke. V) 3 cm with 3 cm GSO array with La. Br 3 array

Summary n n n In order to improve the angular resolution of the Compton camera, we have developed an 8 x 8 array of La. Br 3(Ce) pixels with a size of 6 x 6 x 15 mm 3 , sealed in a compact package, and a gamma camera based on the array coupled to a 64 ch MAPMT(HPK H 8500). Light output uniformity among 64 pixels is 20%(RMS). Energy resolutions (FWHM) at 662 ke. V are 38 38 mm 3 monolithic: 3. 1 0. 3% 8 8 array with SAPMT: 4. 9 0. 7% 8 8 array with MAPMT by resistor-chain readout: 6. 3(Av. of 64 pixels) 1. 2(RMS)% Angular resolutions (FWHM) of the Compton camera using the La. Br 3 array are 6. 1 and 4. 0 at 364 ke. V and 662 ke. V, respectively. For future work, we will make four arrays to cover an area of 10 x 10 cm 2, and develop a readout system by which each anode is read individually to improve the energy resolution.