Compton Gamma-ray Imager Using Electron Tracking Gaseous TPC and Scintillation Camera Dept of Physics, H.Kubo, Kyoto University K.Hattori, K.Miuchi, T.Nagayoshi, H.Nishimura, Y.Okada, R.Orito, H.Sekiya, A.Takada, A.Takeda, T.Tanimori � Advanced Compton gamma-ray imaging method � Performance of prototype camera � Improvement � Summary
Sensitivity in the X/gamma-ray region keV MeV GeV TeV Our Goal A l l S k y S u r v e y 0 . 2 ～1 0 0 M e V
Advanced Compton Imaging � Gaseous TPC track and energy (present) of recoil electron 10cm � Scintillation camera position and energy 30cm of scattered γ -ray (balloon) 50cm Reconstruct Compton scattering (satellite) event by event 1 photon ⇒ direction + energy No collimator ⇒ Large FOV (~ 3str) Kinematical background rejection For ~ 10MeV γ -ray, tracks of e + e - in pair production process are measured
Readout of gaseous TPC ( µ -PIC) Micro pattern gas chamber 2D readout (256x256pixels) Large detection area (10cm × 10cm) 10cm Print Circuit Board technology max gas gain ~ 16000 energy resolution 30% @ 5.9keV (100cm 2 ) stable operation for 1000h @ gas gain ~ 6000 good gas gain uniformity 4.5% @ 100cm 2 fine position resolution (~ 120µ m)
Gaseous-TPC (µ− TPC) Electric field � 10cm × 10cm µ -PIC ⇒ 2D hit position ( ∆ = 120 µ m) � 8cm drift cage Velocity ⇒ drift time ⇒ Z position = 4cm/ µ sec ( ∆ = 800 µ m/FPGA CLK) 3D track of a charged particle is measured Typical tracks Ar 90% C 2 H 6 10% gas gain ~ 5000 proton E ~ 1MeV electron E ~ 500keV
Scintillation Camera Classical Anger camera 4” × 4” × 1” NaI(Tl) scintillator 5 × 5 Hamamatsu ¾” R1166 PMTs Photocathodes cover 40% area No DOI measurement 2 D P o s i t i o n r e s o l u t i o n 1 0 c m ～ 7 . 5 m m ( F WH M , 6 6 2 k e V ) E n e r g y r e s o l u t i o n 1 c m 9 . 1 % @ 6 6 2 k e V ( F WH M )
Prototype Compton camera No Veto or Shield ! memory board preamp on VME bus Anger camera NaI(Tl): 10x10x2.5cm 3 30cm RI source Position encoder µ -TPC ( µ -PIC) 10x10x8cm 3
Result of γ -ray imaging 137 Cs(662keV) image 15 with prototype camera No cut Measure 3D track of Compton recoil e - & energy and direction of scattered γ Y [cm] energy of incident γ is known parameter reconstruction of incident γ -ray source Background rejection -15 -15 X [cm] 15 α geo : measured α α cut α kin : calculated α from α geo ~ α kin 15 after α cut energy information α geo - α kin incident γ Y [cm] recoiled e - source -15 scattered γ -15 X [cm] 15
Comparison with the classical Compton method Advanced Compton Method Classical Compton Method Using the electron tracks Not using the electron tracks • error region of direction is in ring form in sector form Simply overlay Simply overlay 2 sources were Hard to separate separated clearly 2 sources 15 15 150 events Y [cm] Y [cm] 600 events -15 -15 -15 X [cm] 15 -15 X [cm] 15 137 Cs(1MBq) × 2 137 Cs(1MBq) × 2
Angular resolution gain ~ 5000 SPD cf. MEGA gain ~ 6000 Si tracker + CsI(Tl) gain ~ 5000 • ARM 13.4 ° (2MeV, FWHM) ARM • SPD 84 ° (1.8MeV, FWHM) gain ~ 6000 A.Zoglauer, et. al. IEEE Trans. Nucl. Sci. in press 34 ° @ 662keV FWHM � SPD (Scatter Plane Deviation) � ARM (Angular Resolution Measure) 16 ° @ 662keV FWHM for each gamma-ray
137 Cs(662keV) reconstructed Gamma-ray imaging spectrum for unknown energy sources Measure scattered γ ‘s energy & direction recoiled e - ‘s energy & direction 0 400 800 1200 Full reconstruction of Energy [keV] incident γ 15 Reconstructed image � Angular res. (RMS) ARM ~ 15 ° Y [cm] SPD ~ 35 ° source -15 -15 X [cm] 15
Improvement of gaseous TPC: µ -TPC with conductive capillary plate stable gas gain of µ -PIC ~ 6000: not enough for MIP ⇒ Intermediate gas multiplier(X10) Capillary Plate is used Hamamatsu Photonics 10cm 40M Ω Track of cosmic-ray Muon was detected clearly 4mm P10 1atm 10cm
Improvement of scintillation camera: Pixellated CsI(Tl) coupled to Multi-anode PMT 6x6x20mm 3 CsI(Tl) Charge division with 65 µ mt reflector readout with 8x8 resistor chain array Reconstructed γ -ray image 20 ｍｍ ５ ０ ｍｍ Energy Resolution 8x8 multi-anode PMT 9.0%@662keV (HPK Flat-panel H8500) (FWHM) ５ ０ ｍｍ
Other improvements � Scintillation camera � NaI(Tl) Anger camera 10x10cm 2 ⇒ 37x37cm 2 � Pixel array: CsI(Tl) 20mmt ⇒ GSO(Ce) 13mmt(1 rad. length) to reduce DOI error � Readout with low power ASIC(IDE VA32_hdr11/TA32cg) � µ -TPC : 10x10x8 cm 3 ⇒ 30x30x30 cm 3 37cm 49mm GSO(Ce) µ -PIC 37x37cm 2 NaI(Tl) 8x8 array Anger camera
Summary � We developed Compton gamma-ray imager using electron tracking gaseous TPC and scintillation camera � Event by event reconstruction was successful � Good background rejection capability ⇒ higher S/N than that of classical Compton Meth. � Prototype performance for 662keV gamma-ray • ARM(FWHM) 16 ° SPD(FWHM) 34 ° Goal: All sky survey in sub-MeV and MeV region with better sensitivity by order of mag. than COMPTEL 500keV(FWHM) ARM ~ 7 ° SPD ~ 20 ° ARM ~ 5 ° SPD ~ 15 ° 1MeV(FWHM)
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