N14-4 IEEE NSS/MIC 2014 @ Seattle Effectiveness and Performance of a Full Ray-Tracing Sub-MeV Compton Imager Yoshitaka Mizumura (Kyoto Univ.) A. Takada, S. Iwaki, S. Komura, H. Kubo, Y. Matsuoka, K. Miuchi, T. Mizumoto, K. Nakamura, S. Nakamura, M. Oda, J. D. Parker, S. Sonoda, T. Sawano, T. Tanimori, D. Tomono
Sub-MeV/MeV gamma-ray astronomy Treasure box of All-sky MeV map Interesting Science 1 — 30 MeV CGRO/COMPTEL Nucleosynthesis SNR, Galactic plane Particle acceleration ~30 objects/10 years Relativistic Space Jet Strong gravitational potential V. Schönfelder+ (A&AS, 2000) Blackhole, accretion disk Evolution of the Universe Most-distant GRB Others Solar flare, Gamma-ray pulsar Large Field of View Requirements for the next High quality image generation telescopes Wide-band detection 2
Difficulty of MeV gamma-ray imaging Compton scattering dominates in MeV cross section Principle of Compton Imager Unclearness Recoil electron & E 1 Artifacts Scattered gamma E 2 Radioactivation by cosmic-rays -> Huge background in space Improvement of imaging Background suppression are two big tasks in MeV 3
E lectron- T racking C ompton C amera ( ETCC ) Ray-Tracer (Gas TPC) Drift velocity ~6 cm/us Observed Ray track samples electron muon pair-creation shower candidate 30 cm 1 m 30 cm 4
Effectiveness of Ray-Tracing information Three additional parameters 1. SPD , Direction of scattering plane -> Event by event arrival direction 2. dE/dx , Energy deposit rate of particle -> Background rejection by particle identification electron 3. α , Angle between scattered gamma and recoil electron scattered -> Background rejection by kinematics test gamma Image of three 137 Cs (662 keV) sources dE/dx with/without ray tracing info. No track info. With track info. Ray-Tracing info. enables us to detect the sources by factor ~3 in significance 5
ETCC for 2 nd balloon exp. (SMILE-II) S ub- M eV gamma-ray I maging L oaded-on-balloon E xperiment Aim : Confirmation as a sub-MeV telescope -> Imaging of Crab/Cyg X-1 ( >3 σ detection, ~40 km, one-day flight) Required Performances Effective area: >0.5 cm 2 (@300 keV) 1 m Angular resolution: <10 o (@600 keV) SMILE-II flight model 5.3 o (@ 662 keV) SMILE-III sim. (30 cm) 3 Xe 3 atm, 3 R.L. scintillator 0.7 cm 2 (@ 300 keV) SMILE-II flight model SMILE-I type 10 cm ETCC Clear the requirements!! 6
Other Performances of SMILE-II FM Energy resolution Field of View −0.5 Δ𝐹 𝐹 𝐹 [%] = 10.7 × 662 keV Imaging check for large zenith angles 137 Cs (662 keV, 0.7 MBq) at 2 m distance from ETCC SMILE-II flight model ETCC has large FoV ~2 π str 7
ETCC in intense radiation field Balloon/Satellite altitude has intense background radiation -> Can ETCC image a gamma-ray source in such field? water Protons We generate φ20cm (140 MeV) factor ~5 more intense field than Shield plate expected BG Protons 137 Cs (0.8 MBq) n, γ, p, … 100cm 662 keV Plastic Scintillator 30cm 30cm Gas TPC ETCC has imaging capability in intense BG GSO scinti. 8
ETCC as a gamma-ray polarimeter Simulation Experiment Normalized counts 100% polarized 356 keV max gamma rays Polarization min Cos θ < 0.7 SMILE-II Azimuth angle [deg.] 𝑛𝑏𝑦−𝑛𝑗𝑜 Modulation Factor (MF) = 𝑛𝑏𝑦+𝑛𝑗𝑜 133 Ba is set at Φ =90 o MF vs. Energy MF vs. Incident angle < 320 keV (@ 200 keV) (@ 0 deg.) MF = 0.5 MF = 0.5 Fit Eq. 400 60 o A + B sin(2Φ+C) keV Azimuth angle Φ [ deg] ETCC has large MF which can detect low S/N polarization 9
Summary Ray-Tracing info. brings big benefits for Compton imager High quality/contrast imaging ( SPD ) Efficient background rejection ( dE/dx , α ) SMILE-II ETCC fulfills the requirement performances Effective area: 0.7 cm 2 (@ 300 keV) Angular resolution: 5.3 deg. (@ 662 keV) Energy resolution: 10.7% x (E/662 keV) -0.5 Wide Field of View: ~2 π str (@662 keV) Imaging capability in intense radiation field As a background-suppressed imaging polarimeter Modulation Factor: >0.5 (E < 400 keV, Zenith angle < 60 o ) SMILE-II ETCC can detect Crab (>3 σ , several hours) Negotiation with NASA/GSFC for balloon flight(s) @ fort sumner is ongoing 10
Thank you for your attention!! Please visit to the SMILE project web page http://www-cr.scphys.kyoto-u.ac.jp/ research/MeV-gamma/index_e.html 11
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