Precise Low-Energy Electron Tracking Using a Gaseous Time Projection Chamber for the Balloon-Borne Gamma Ray Compton Telescope T. Mizumoto, T. Tanimori, H. Kubo, A. Takada, J. D. Parker, S. Sonoda, Y. Mizumura, D. Tomono, T. Sawano, K. Nakamura, Y. Matsuoka, S. Komura, Y. Sato, S. Nakamura, K. Miuchi, S. Kabuki, Y. Kishimoto, S. Kurosawa, S. Iwaki, M. Tanaka, M. Ikeno, T. Uchida Contents i. MeV gamma ray astronomy ii. Electron Tracking Compton Camera and SMILE-II iii. New DAQ system for SMILE-II ETCC iv. Performances of SMILE-II flight model ETCC 2013 IEEE Nuclear Science Symposium, October 29, 2013 @ COEX, Seoul, Korea, N10-2
Motivation (sub-mev/mev gamma-ray astronomy) Nucleosynthesis SNR : Radio-isotopes Galactic plane : 26 Al 60 Fe Annihilation Acceleration GRB, Jet (AGN) : Synchrotron + Inverse Compton Strong Gravitational Potential Black Hole : accretion disk, π 0 Etc. Gamma-ray Pulsar, solar flare Bad Sensitivity Good erg / (cm 2 sec) Astro-H Sensitivity Fermi EGRET Obs. Time : 10 6 sec Air Cherenkov The observation of continuum component is important. Where are MeV gamma-ray objects? There are many background events which obstruct the observations. Requirements for the next-generation detectors are Wide-band detection Large Field of View Background rejection
Electron Tracking Compton Camera (ETCC) for SMILE μ-tpc GSO ASIC FPGA 1 m GSO Schematic of ETCC (left) and photograph of flight model ETCC for SMILE-II experiment (right) SMILE experiment μ T P C G S O SMILE-I (2006) SMILE-II Size (10 10 15)cm 3 (30 30 30)cm 3 Readout Number Readout Pitch pixel number 256 strips /10 cm 384 strips /30 cm 400 μm 800 μm 2112 pixels 6912 pixels
370 mm 22 cm (10 10 15)cm 3 μ -TPC &GSO μ-tpc readout for SMILE-I and SMILE-II SMILE-I ETCC (30cm) 3 μ -TPC SMILE-II ETCC 11.8 cm GSO readout circuit ASD(256ch/10cm) 4.5 kg 560 mm GSO & GSO readout circuit 1 m 1 m SMILE-I FM ETCC encoder(1 board/1etcc) 7.8 kg SMILE-II FM ETCC new readout board (128 strips/10 cm) conventional readout circuit... massive takes up a lot of space high electric power consumption ASIC chip transistor type strip number per 1 ASIC chip ASD system (for SMILE-I) bipolar transistor 4 16 new readout board (for SMILE-II) CMOS transistor ->developed new readout circuit power consumption 0.24 W/strip 0.17W/strip
1 10 100 1000 Cathode 100MHz clock(0-1023) Anode Example TPC data of SMILE-II ETCC with new readout board TPC hit data TPC FADC data muon track electron track TPC 3D reconstructed track (SMILE-II ETCC) muon track electron track strip number(0-383) SMILE-I 10cm ETCC SMILE-II 10cm ETCC Number of hit pixel strips SMILE-II 30cm ETCC 0 100 200 300 TPC 3D reconstructed hit data (SMILE-I ETCC) Changed saving method of TPC hit data particle tracks are clearer than ever We can detect recoil electrons perfectly
Example data of SMILE-II ETCC with new DAQ system 137 Cs(0.85MBq) zenith = 0 z = 2055 mm 137 Cs source ETCC reconstructed incidentγ φgeo φkin Incidentγ (to source) Scatter Point PC for command sending Track range Absorption Point We can reconstruct the incident gamma rays by using the scattering point, direction and gamma ray energy, recoil direction and electron energy event by event.
point sources Performances of SMILE-II FM ETCC measurement 10 simulation present value Since we can detect almost all scattered electrons, the measured efficiency is similar to the simulated one. incident γ scattered γ recoil electron ARM : accuracy of the scattering angle SPD : accuracy of the scattering plane effective area 10cm 2 -> reach the efficiency of COMPTEL Legacy and Advanced Compton Imaging ARM 5.3º (FWHM) @662keV SPD 93º (FWHM) @662keV
1088mm In the environment of high background, SMILE-II ETCC system operates correctly and shows powerful imaging ability. Further analysis of the data will be done. Measurement in the environment of high background level (@RCNP Osaka Univ.) Date 2013/10/17 trigger rate : 16.2 khz data saving event rate : 394 Hz Dead Time : 59.6% 137 Cs: 0.84 MBq MIP neutron & proton event Compton e- no cut TPC volume cut volume cut + de/dx cut target (water) lead proton beam 137 Cs source Track range vs energy(de/dx) ETCC target source (-125,167) Energy Spectra after energy cut around 662 kev 30cm ETCC proton beam
Conclusion We have been developing the flight model (30 cm) 3 ETCC for SMILE-II experiment. Since we changed the algorithm for taking track hit data of μ-tpc, hit number per event is increased, and almost all recoil electron can be taken. From the result of the simulation, we can achieve the efficiency 10 times higher than the present one by changing the gas species and pressure of the TPC. For SMILE-II ETCC, we confirmed the detector operates correctly in the high background rate.
Fin My colleagues S. Komura, NPO2-122, Performance Improvement of an Electron- Tracking Compton Camera by a New Track Reconstruction S. Sonoda, M12-10, The Performance Evaluation of the Electron Tracking Compton Camera D. Tomono, N28-2, First Application to Environmental Gamma-Ray Imaging with an Electron Tracking Compton Camera