Gamma- r ay Imaging with a L ar ge mic r o- T PC and a Sc intillation Came r a Kyoto University dept. of physics Cosmic-ray group K. Hattori Contents 1. MeV gamma-ray astronomy 2. Principle of Compton Imaging 3. μ -PIC (Micro Pixel Chamber) with a large detection area + GEM (Gas Electron Multiplier) Micro-TPC with a large detection volume (Time Projection Chamber based on μ -PIC) 4. Performance of Compton camera 5.Summary 22/2/2007 11th Vienna Conference on Instrumentation
De te c tio n Se nsitivity in the X/ gamma- r ay GeV keV MeV TeV band Sensitivity(ergs cm -2 s -1 ) EGRET Our Goal MeV band 1mCrab Air � COMPTEL GLAST(2007) Cherenkov (CGRO) � INTEGRAL 10 times as high sensitivity as that of COMPTEL All-sky survey ～１° MeV band ∙ ∙ ∙ ∙ ∙ Low sensitivity 22/2/2007 11th Vienna Conference on Instrumentation
Princ iple o f Classic al Co mpto n I maging Photon ∙ ∙ ∙ ∙ ∙ main interaction in MeV band Compton scattering incident gamma-ray Distribution of TOF (time-of-flight) liquid scintillator background signal Recoil electron energy loss, location, time 1.5m NaI(Tl) scintillator G. Weidenspointner ’ et al., Scattered gamma-ray 2001. A&A 368, 347. Energy loss, location, time Recoil electrons 1.7m are not tracked The origin of a single event can be restricted by the “event circle” The gamma-ray originated at the point of overlap low background rejection power 22/2/2007 11th Vienna Conference on Instrumentation
Princ iple o f Advanc e d Co mpto n Came ra ( μ -PIC) base d o n Mic r o Pixe l Chambe r 2-dimensional imaging gaseous detector PC (gas de te c to r) mic r o- T gy and tr e ne r ac k o f a re c o il e le c tro n Ange r c ame r a sc intillation de te c tor NaI (T l)(surro unding mic ro -T PC) e ne rgy and po sitio n o f a sc atte re d gamma-ray Having tracks of recoil electrons… 1photon : r e c onstr uc te d c omple te ly gas de te c tor e ne r gy and dir e c tion le ss c ollisions High bac kgr ound the dir e c tion of r e c oil e le c tr on → le ss e r r e je c tion powe r r or Unnecessary to use a TOF value and a collimator 22/2/2007 11th Vienna Conference on Instrumentation
μ –PI C (Mic ro Pixe l Chambe r) 2-dimensional imaging 400 μ m gaseous detector electrode pitch 400 μ m prototype of Compton camera based on a μ -PIC with a detection area of 10 cm × 10 cm 10cm Stable operation Max gas gain ～ 15000 @gas gain ~ 6000 position resolution ~120 μ m Electric field 22/2/2007 11th Vienna Conference on Instrumentation
De ve lo pme nt o f large μ -PI C 400 μ m Goal 10 times as high sensitivity as that of COMPTEL To attain goal….. prototype (10 cm × 10 cm) is not enough large μ -PIC with a detection area of 30 cm × 30 cm gain max : 7,000 30 cm stable gas gain : 2,000 μ -PIC To detect Compton events · · · · · detection of recoil electrons using the micro-TPC ～ 2 ~ 3 × MIPs (Minimum Ionizing Particle) Energy loss of recoil electrons required gas gain 2 × 10 4 (We have not achieved because of discharge) Another electron multiplier is necessary GEM (Gas Electron Multiplier) F.Sauli(1997) operated @ low gas gain(~10) 22/2/2007 11th Vienna Conference on Instrumentation
28 cm Mic ro -T PC base d o n μ -PI C and GE M 23cm GEM segmented GEM (8 segments) to reduce capacitance and thus damage caused by discharge 23 cm × 28 cm (limited by material size) Standard Scienergy Co. Ltd, Japan GEM design 70 μ m -HV just above the μ -PIC GEM was installed 140 μ m Cu dr ift plane (5 μ m) -HV electron cloud 14.5c m 0.41kV/ c m 10M Ω polyimide (50 μ m) GE M 0.5c m 2kV/ c m 10M Ω μ - PIC -HV A charged particle runs in the micro-TPC and makes electron clouds, and then electorn clouds are pre-amplified by the GEM and then the μ -PIC 22/2/2007 11th Vienna Conference on Instrumentation
Pe rfo rmanc e o f μ –PI C and GE M using Ar-C2H6(90:10) gas 10 4 1atm Maximum gas gain of 5 × 10 4 Stable gas gain 2 × 10 4 μ -PIC 2 × 10 3 × 10 3 GEM 10 22/2/2007 11th Vienna Conference on Instrumentation
Mic ro -T PC was ke pt in the se ale d ve sse l μ -TPC The micro-TPC was set in a aluminum vessel filled with Ar-C 2 H 6 (90:10) gas vessel to a pressure of 1 atm sealed for the duration of the measurements. Anode:768ch + cathode:768ch 30cm → Signals from the μ -PIC are sent via the printed boards drift cage 15cm from μ -PIC 256ch per board printed board Outside μ -PIC pre -amplifier to pre-amplifiers Sealed vessel 22/2/2007 11th Vienna Conference on Instrumentation
DAQ syste m Position e nc oding ASD (amplifie r module (100MHz F PGA) - mic r o- T PC 1536 ch digital shape r - disc r iminator ) 11cm 32bit 21cm anode 768 ch cathode 768h summed analog (8ch) VME Me mor y Boar d Recording anode and Cathode coincident positon and the timing VME F ADC 100MHz 8c h × 3 Recording summed analog signals 22/2/2007 11th Vienna Conference on Instrumentation
Pe rfo rmanc e o f the mic ro -T PC(1) direct X-ray (31 keV) Irradiation of 133 Ba with the whole Gain uniformity rms 13.9 % detector 10cm × 10cm μ -PIC 5% gain 2.3 × 10 4 the peak of copper fluorescent Energy resolution X-rays at 8.0 keV, generated at the GEM and the μ -PIC by the original X-rays from 133Ba the energy resolution was worse at 59.5 keV It might be due to the saturation of the ASD chips gain 2.3 × 10 4 22/2/2007 11th Vienna Conference on Instrumentation
Pe rfo rmanc e o f the mic ro -T PC(2) Two plastic scintillators were used in coincidence for cosmic muon trigger Position resolution Difference between hit points and tracks obtained from fitting 15cm 2 2 ( l ) σ = σ + σ detctor diffusion 2 2 ( ) D l = σ + detector 30cm 30cm 0 . 51 mm, D 0 . 37 mm σ = = 30cm detector Total gas gain of 5 × 10 4 l :drift length 22/2/2007 11th Vienna Conference on Instrumentation
Co mpto n Came ra Anger camera scintillation detector for scattered gamma-rays μ -TPC Anger A large NaI(Tl) crystal and 6 × 6PMTs 45cm camera γ source γ e - 37cm 6x6 = 36PMTs encoder ASD Position resolution < 11mm(FWHM) � Effective Area (No image distortion) ~30x30cm 2 � Energy Resolution 7.4%(FWHM)@662keV,11.2%(FWHM)@80keV � Dynamic range 80keV-1.5 MeV � 22/2/2007 11th Vienna Conference on Instrumentation
Pro to type o f Advanc e d Co mpto n Came ra Imaging Quality (662keV two sources ) Imaging Quality (662keV two sources ) We have developed Electron-tracking telescope Prototype of Compton 50 SPD~40 o Camera based on 40 150 events 10cm × 10cm μ -PIC 30 Event Arc (smoothing) 20 10 z 9 10 8 0 7 6 -10 5 4 -20 3 012345678910 x -30 2 1 -40 0 10 9 8 -50 7 6 y 5 -50 -40 -30 -20 -10 0 10 20 30 40 50 4 3 2 1 Line source 0 I-131 (364 keV) Classical Compton telescope 50 1625 events 40 Event Circle 30 (smoothing) 10 z 9 20 8 10 7 6 0 5 -10 4 3 -20 012345678910 2 x -30 1 0 -40 10 9 8 7 6 5 y 4 3 2 1 -50 0 -50 -40 -30 -20 -10 0 10 20 30 40 50 22/2/2007 11th Vienna Conference on Instrumentation
Pe rfo rmanc e o f Co mpto n Came ra(1) based on 23 cm × 28 cm × 15cm micro-TPC Typical Compton event Typical recoil electron tracks 137 Cs (662 keV) Irradiating 137 Cs (662 keV) Micro-TPC Scattered 137 Cs source gamma-ray Reconstructed gamma-ray 15cm Recoil electron Anger camera E μ -PIC : 78.02 keV 30cm E scinti : 615.9 keV 30cm 22/2/2007 11th Vienna Conference on Instrumentation
Pe rfo rmanc e o f Co mpto n Came ra(2) 137 Cs 662 keV using data with reconstructed energy 610 keV ~ 760 keV 137Cs (1 MBq) × 2 137Cs (1 MBq) 137Cs (1 MBq) 43cm point source ~45 cm from micro-TPC 22/2/2007 11th Vienna Conference on Instrumentation
Pe rfo rmanc e o f Co mpto n Came ra(3) Error concerned with the reconstructed direction of a Incident gamma is determined event by event � ARM (Angular Resolution Measure) Concerned with the angle between the scattered gamma-ray and the recoil electron � SPD (Scatter Plane Deviation) Determination accuracy of the plane formed By the scattered gamma-ray and the recoil electron 137 Cs (662 keV) ARM = 9.95 ˚ (FWHM) SPD = 159 ˚ (FWHM) Well fitted by Lorentzian 22/2/2007 11th Vienna Conference on Instrumentation
Summary & F uture Wo rks PMT (H8500) Micro-TPC based on 23cm × 28cm GEM � and 30cm × 30cm μ -PIC effective volume 23cm × 28cm × 15cm Gain uniformity rms 13.9 % 5cm energy resolution FWHM 37.5% (31.0 keV) Large Compton camera � 16 × 16 recoil electron tracks were successfully obtained pixels point source imaging using 137 Cs (662 keV) 3 mm ARM 9.96 ˚ (FWHM) SPD 159 ˚ (FWHM) 13mm Future Works � Imaging using source with various energy (350 keV ~ a few MeV) To obtain better position resolution of scattered gamma-rays….. Anger camera ( < 11mm FWHM ) → Pixel scintillator ( < 3mm FWHM) Goal FWHM � ARM 7 ˚ SPD 40 ˚ 500 keV 5 ˚ 20 ˚ 1 MeV 22/2/2007 11th Vienna Conference on Instrumentation
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