Development of a new MeV gamma-ray camera

Transcription

1 Development of a new MeV gamma-ray camera ICEPP Symposium February 16, 2004 Hakuba, Nagano, Japan Kyoto University Atsushi Takeda H. Kubo, K. Miuchi, T. Nagayoshi, Y. Okada, R. Orito, A. Takada, T. Tanimori, M. Ueno 1. MeV Gamma-ray Astronomy 2. New MeV Gamma-ray Camera 3. Prototype Detector 4. Summary & Future Works

2 1. MeV Gamma-ray Astronomy sensitivity our goal high

3 Expected sources in MeV region Supernova Remnants (SNRs( SNRs) 26 Al(1.8MeV), 44 Ti(1.16MeV), Nuclear gamma Active Galactic Nuclei (AGN) jets Optical Violent Variable (OVV) galaxy, Blazar Black Hole Binaries, Galactic Center, Primordial BH, 511keV Gamma Ray Bursts Polarization Pulsars

4 Mev γ-ray imaging detectors 1. Collimator + Position Sensitive Detector (PSD) Narrow field of view Background from collimator Energy < 1MeV source PSD 2. Single or Multiple Compton (Classical Compton Method) Only event circle No background rejection COMPTEL Low-Z High-Z semiconductor 3. Advanced Compton Method Full event reconstruction Kinematical background rejection Large field of view Single Compton e - Multiple Compton TPC MeV gamma-ray camera γ High-Z

5 COMPTEL (aboard CGRO satellite: 1991~2000) E 0 event axis Classical Compton method energies of scattered γ and recoil e - : E 1, E 2 E 0, φ liquid scintillator (NE213) NaI(Tl) E 2 E 1 positions where scattering and γ absorption occurred event axis direction Only event circle can be determined No background rejection

6 2. New MeV Gamma-ray Camera 1MeV 10MeV Drift plane e - e - e + -PIC PMTs Advanced Compton method micro-tpc (µ( -PIC + TPC) recoil electron energy & track + Scintillation camera scattered energy & position Scintillator Event by event full reconstruction large field of view background rejection

7 Micro PIxel gas Chamber (µ-pic) Key device for the recoil electron tracking High gain > 10 4 Fine position resolution ~120~ 120µm Cathode Anode 400µm 100µm Discharge damage is not serious Cathode Anode 50µm 400µm pitch electrodes 256 anodes and 256 cathodes Printed Circuit Board (PCB( PCB) technology 10cm 10cm

8 Performance of the µ-pic Gas gain Gain map V A = 560V Ar:C 2 H 6 = 8: Ar:C 2 H 6 = 9: Anode voltage [V] Max gain: Ar:C 2 H 6 = 8:2 Anode Cathode Uniformity (s) ~ 7% Stable operation: > 1000 hours with gain of 6000

9 Performance of the µ-pic 55 Fe energy spectrum ( mm 2 ) (10 10cm 2, whole area) Counts Counts % (FWHM) Mn K 5.9keV Counts 30% (FWHM) Ar escape Energy [kev] Energy [kev] Energy [kev]

10 X-ray images obtained with µ-pic Xe:C 2 H 6 = 7:3 probe Test chart image 0.5mm slits banana plug Knife edge test Counts position resolution =120µm Length along the edge [mm]

11 Micro-TPC = -PIC + TPC (x, y) (drift time) 3D tracking Picture of the micro-tpc -PIC 10cm X 10cm Encoder FPGA X 5 20MHz clock Amp boards Amplifier-shaper shaper- discriminator (ASD) chip discrimination digital out TPC 8cm drift length

12 Tracking performance of the micro-tpc Electron tracks Proton track 0.8 GeV/c 2 proton beam ~500 kev/c 2 electron tracks 3-D spatial resolution : 260µm (Ar, 20MHz clock) (limited by DAQ clock of 20MHz) ~210µm using 50MHz DAQ in the near future

13 3. Prototype Detector memory board ASD chips Micro-TPC (µ-pic) 10 X 10 X 8 cm 3 Ar + C 2 H 6 (9:1) encoder RI source No Veto or Shield! NaI(Tl) Anger camera 10 X 10 X 2.5 cm 3 25 PMTs position resolution ~6.7mm (FWHM) energy resolution ~11.2% (662keV, FWHM)

14 Typical reconstructed event Signal wave forms source position reconstructed Compton point NaI hit Top view Side view NaI hit

15 Gamma-ray imaging for known energy sources from track of recoiled e - + energy and direction of scattered γ Cs 662keV Na 511keV 133 Ba 356keV Y [cm] Y [cm] Y [cm] src src src X [cm] X [cm] X [cm] 15 Angular resolution (RMS:662keV) Angular Resolution Measure (ARM): ~15 Scatter Plane Deviation (SPD): ~25

16 Background rejection using redundant angle α geo : measured α kin : calculated α from energy information α cut geo kin Incident γ recoil e ARM -180 SPD geo - kin 0 0 cut cut 15 Y [cm] Y [cm] No cut After α cut X [cm] source 15 source scattered γ X [cm] 15

17 Gamma-ray imaging for unknown energy sources from scattered γ s energy & direction recoiled e - s energy & direction 137 Cs(662keV) reconstructed spectrum Full reconstruction of incident γ Energy [kev] 15 Reconstructed image Angular res. (RMS) ARM ~15 SPD ~35 Y [cm] source X [cm] 15

18 Comparison with the classical Compton method Advanced Compton Meth. Using the electron tracks complete direction within sector form error region Classical Compton Meth. Not using the electron tracks only event circle within ring form error region 15 2 sources were separated clearly even from ~100 events 15 Hard to separate 2 sources 150 events Y [cm] Y [cm] X [cm] events X [cm] 15

19 4. Summary & Future works Event by event full reconstruction well established even for the continuous γ-ray Good background rejection capability higher S/N than that of classical Compton Prototype performance (full reconstruction) ARM(RMS) ~15 SPD(RMS) ~35 ARM (goal: ~3 ) uniformity of micro-tpc higher energy resolution pixelization of scintillator higher position resolution SPD (goal: ~5 ) clock up of micro-tpc (20MHz 50MHz) gas study (Ar CF 4 ) large volume micro-tpc more precise tracking

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22 Crystal structure analysis with RCP * method * RCP: Rotation Continuous Photograph Experimental 10X10cm µ-pic Beam stopper Sample crystal Crystals Goniometer Beam line X-ray generator 50kV, 250mA Mo target 17keV (λ : nm)

23 Clock up of the micro-tpc 20MHz(proton) 50MHz(proton) Clock up Gaps in the drift direction 2mm Higher spatial resolution of micro-tpc 0.8mm More precise tracking of recoiled electron

24 Theoretical limits of angular resolution in the ARM direction Owing to the Doppler broadening of the scattered g-ray energy Angular resolutions (ARM) for various nuclei A.Zoglauer, et.al.(spie,2003) Ar Xe Si CdTe 200keV keV MeV

25 Theoretical limits of angular resolution in the SPD direction Owing to the multiple scattering in the tracking detector Scattering angle (RMS) 500 m Scattering angle (RMS) 5mm Very hard to obtain the precise direction of the recoiled e - in the solid detector

26 Probability [%] Effective area Effective area of COMPTEL ~40cm 1MeV 50cm cube gas detector Compton effective area ~30cm 1MeV (Xe 1atm) 10-2 Gas thickness: 50cm Energy [MeV] Gas detector has enough Compton scattering capability

27 Position Sensitive Scintillation camera NaI(Tl) Scintillator 5 5 Hamamatsu ¾ R1166 PMT PhotoCathode Cover rate 40% Dynamic Range 0.1 1MeV Energy resolution 9.1%@662keV(FWHM) Position resolution 7.5mm(FWHM,662keV)

28 Detection Efficiency 50cm 3 Xe1.5atm 50cm 3 Ar 3atm 30cm 3 Xe 1.5 atm 30cm 3 Ar 3atm Zenith Angle =0 γ e- γ Gas 30cm 3 Xe 1.5 atm All scattered γ Silicon pad Through going electron (δ also improved)

29 30cm 30cm µ-pic Now, we are developing 30 30cm 2 µ-pic.

30 Electronics Preamplifier ATLAS ASD chip 40cm 30cm -PIC Encoding board 5 FPGAs take anode cathode 20MHz

31 Angular Resolution ARM : Angular Resolution Measure SPD : Scatter Plane Deviation SPD 30cm Xe 1.5 atm Effective Area θ Large field of view 2str(FWHM) 30cm Xe 1.5 atm(1mev)