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講演・口頭発表等 - 田島　宏康

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Suppressing Optical Cross Talk in Silicon Photomultipliers 国際会議

Hiro Tajima, Akira Okumura, Naoya Hidaka, Yuki Nakamura, Nobuhito Yamane, Anatolii Zenin

International Conference on the Advancement of Silicon Photomultipliers

開催年月日： 2018年6月

記述言語：英語会議種別：口頭発表（一般）

開催地：Schwetzingen, Germany 国名：ドイツ連邦共和国

Compared to conventional photomultiplier tubes (PMTs), silicon photomultipliers (SiPMs) based on multi-cell geiger-mode avalanche photodiodes (GAPDs) have advantages with regards to photon detection efficiency, compactness, robustness and tolerance of both magnetic fields and intense light sources. In addition, SiPMs can be cost effective for applications that require many channels with small unit area. Because of these advantages, SiPMs are starting to replace PMs in many applications.
When used in the cameras of Imaging Atmospheric Cherenkov telescopes, the optical crosstalk of SiPMs needs to be reduced in order to suppress accidental triggers due to the high rate of night sky background caused by scattered starlight and moonlight, and the fluorescence of excited molecules in the atmosphere.
In this contribution, the propagation properties of optical photons in SiPMs are investigated through systematic measurements of the optical crosstalk with varying SiPM pixel and GAPD cell sizes and with and without coatings on the SiPMs. It was observed that a significant portion of the optical crosstalk is mediated by the coating. The propagation of optical photons in the bulk silicon of the SiPM is also discussed.

Indirect searches for dark matter with gamma rays and other messengers 招待有り

Hiroyasu Tajima

The first KMI School

Evaluation of Silicon Photomultipliers for Dual-Mirror Small-Sized Telescopes of CTA 国際会議

Hiro Tajima for CTA ASTRI and GCT projects

8th International Conference on New Development in Photodetection

開催年月日： 2017年7月

記述言語：英語会議種別：口頭発表（一般）

開催地：Tours, France 国名：フランス共和国

All camera designs for Small-Sized telescopes (SSTs) proposed for the Cherenkov Telescope Array (CTA) utilise silicon photomultipliers (SiPM) as their baseline photon sensor technology. The dual-mirror SST (SST-2M) has a smaller plate scale (i.e. image size) than the single-mirror SST, allowing it to employ 2,000 square SiPMs with pixel sizes of approximately 6 mm, close to the mainstream SiPM sizes.
In CTA, the night sky background level of typically ~25 Mcount/s/pixel (> 100 Mcounts/s/pixel at maximum) places severe constraints on the trigger capability due to accidental coincidence on neighbouring pixels. In order to suppress such events, it is necessary to reduce optical crosstalk, a mechanism whereby a single optical photon can produce multiple avalanches in the SiPM, while keeping good photon detection efficiency. These are, in general, contradicting requirements.
In this talk, we report on characterisation of a variety of SiPM technologies for SST-2M cameras and compare results obtained at different participating institutions. We assess the harmonisation of results and discuss the likely performance that will be achieved for the first production cameras.

Search for PeVatrons with Imaging Cherenkov Telescopes 招待有り

田島宏康

CRC将来計画タウンミーティング

Indirect Searches for WIMP Dark Matter 招待有り

Hiroyasu Tajima

Physics in LHC and the Early Universe

Quest for the Origin of Cosmic Rays with Gamma-Ray Observations 招待有り

Hiroyasu Tajima

The 3rd International Symposium on "Quest for the Origin of Particles and the Universe"

開催年月日： 2017年1月

記述言語：英語会議種別：口頭発表（招待・特別）

開催地：Nagoya University 国名：日本国

Cosmic rays are among long standing mysteries of the Universe since the origin and the acceleration mechanism of cosmic rays are not known well. Gamma-ray observations are expected to play a prominent role in probing into those questions since gamma rays are produced by interaction of cosmic rays. In fact, the Fermi Gamma-ray Space Telescope found the first undeniable evidence of cosmic ray acceleration in supernova remnants (SNRs) in 2013. However, it is not yet conclusive whether the SNRs is the sole origin of Galactic cosmic rays and we also have no credible clues on the extragalactic origins. In this talk, recent progresses and future prospects on uncovering the origins of Galactic and extragalatic cosmic rays are reviewed.

Tracking with Fermi LAT 国際会議

Hiroyasu Tajima

23rd International Workshop on Vertex Detectors

Quest for Dark Matter with Cosmic Gamma-ray Observations 国際会議

Hiroyasu Tajima

KMI International Symposium 2013 on “Quest for the Origin of Particles and the Universe”

Particle Physics and Astrophysics by Cosmic Gamma-ray Observations 国際会議

Hiroyasu Tajima

KMI Inauguration Conference on "Quest for the Origin of Particles and the Universe"

Soft gamma-ray detector for the ASTRO-H Mission 国際会議

ASTRO-H SGD team

SPIE Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray

開催年月日： 2010年6月 - 2010年7月

記述言語：英語会議種別：口頭発表（一般）

開催地：San Diego, CA, USA 国名：アメリカ合衆国

ASTRO-H is the next generation JAXA X-ray satellite, intended to carry instruments with broad energy coverage and exquisite energy resolution. The Soft Gamma-ray Detector (SGD) is one of ASTRO-H instruments and will feature wide energy band (40-600 keV) at a background level 10 times better than the current instruments on orbit. SGD is complimentary to ASTRO-H's Hard X-ray Imager covering the energy range of 5-80 keV. The SGD achieves low background by combining a Compton camera scheme with a narrow field-of-view active shield where Compton kinematics is utilized to reject backgrounds. The Compton camera in the SGD is realized as a hybrid semiconductor detector system which consists of silicon and CdTe (cadmium telluride) sensors. Good energy resolution is afforded by semiconductor sensors, and it results in good background rejection capability due to better constraints on Compton kinematics. Utilization of Compton kinematics also makes the SGD sensitive to the gamma-ray polarization, opening up a new window to study properties of gamma-ray emission processes. The ASTRO-H mission is approved by ISAS/JAXA to proceed to a detailed design phase with an expected launch in 2014. In this paper, we present science drivers and concept of the SGD instrument followed by detailed description of the instrument and expected performance.

Fermi Observations of High-energy Emission from Gamma-Ray Bursts 国際会議

Hiroyasu Tajima

TeV Particle Astrophysics 2009

Polarimetry with ASTRO-H Soft Gamma-ray Detector 国際会議

Hiroyasu Tajima

The coming of age of X-ray polarimetry

開催年月日： 2009年4月

記述言語：英語会議種別：口頭発表（招待・特別）

開催地：Rome, Italy 国名：イタリア共和国

ASTRO-H is a next generation JAXA X-ray satellite to be launched in 2014. Soft Gamma-ray Detector (SGD) onboard ASTRO-H is a semiconductor Compton camera with a narrow field-of-view (FOV) to achieve very low background. Although the SGD is primarily a spectrometer in the 40-600 keV energy band, it is also sensitive to polarization in the 50-200 keV energy band. This paper describes instrument design, expected performance, and experimental validation of polarimetric performance of the SGD.

Compton Camera for Space and Security Applications 国際会議

Hiroyasu Tajima

IEEE Nuclear Science Symposium, Compton Camera Workshop

Detectors for Cosmic Rays on Ground and in Space 国際会議

Hiroyasu Tajima

11th Vienna Conference on Instrumentation

開催年月日： 2007年2月

記述言語：英語会議種別：口頭発表（招待・特別）

開催地：Vienna, Austria 国名：オーストリア共和国

The origin of the cosmic rays has been a great mystery since it was discovered by Victor Hess in 1912.
AGASA observation of ultra-high-energy cosmic-rays (UHECR) possibly beyond GZK (Greisen, Zatsepin and Kuzmin) cutoff stimulated the field in great deal.
In addition, Kamiokande detection of neutrinos from SN1987A and H.E.S.S. detection of TeV gamma-rays from supernova remnants demonstrated viability of neutrino and TeV gamma-ray astronomy for cosmic-ray research.
New generation of currently-operating or soon-to-be-operating detectors for charged particles, gamma-rays and neutrinos from cosmos will get us even closer to understanding the nature and origin of cosmic-rays.
Detectors for UHECRs, gamma-rays and neutrinos are of particular importance in order to study the origins of cosmic-rays since these particles are free from the deflection due to magnetic fields.
Detectors for antiparticles and gamma-rays would be useful to detect cosmic-rays originated from the decay of the dark matter in the Universe.
I will review these cosmic-ray detectors with particular attention on the differences of ground-based, balloon-borne and satellite-borne detectors.

Suppressing Optical Cross Talk in Silicon Photomultipliers

Hiro Tajima, Akira Okumura, Naoya Hidaka, Yuki Nakamura, Nobuhito Yamane, Anatolii Zenin

International Conference on the Advancement of Silicon Photomultipliers 2018年6月11日

記述言語：英語会議種別：口頭発表（一般）

開催地：Schwetzingen, Germany

Indirect searches for dark matter with gamma rays and other messengers 招待有り国際会議

Hiroyasu Tajima

The first KMI School 2018年2月28日

Indirect Searches for WIMP Dark Matter 招待有り国際会議

Hiroyasu Tajima

Physics in LHC and the Early Universe 2017年1月9日 Grant-in-Aid for Scientific Research on Innovative Areas "New expansion of particle physics of post-Higgs era by LHC revealing the vacuum and space-time structure"

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