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| Titel |
The development of infra-free and portable muon counting system with Hamamatsu MPPC |
| VerfasserIn |
Ryuichi Nishiyama, Akimichi Taketa, Hiroyuki Tanaka |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250049130
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| Zusammenfassung |
| We will report the development plan of an infra-free, portable and low-cost muon counting
system with Hamamatsu MPPC (Multi-Pixel Photon Counter), which will achieve more
frequent observations.
Muon radiography has been performed in several volcanoes and clarified the inner density
structure of lava-domes. The observation at Satsuma-Iojima Island (Tanaka et.al,2009) found
the density deficit which indicates the existence of high porosity region, and in
Mt.Showa-Shinzan in Usu (2007), the density excess was detected which implies the
intrusive magma. Its shape would be relevant to magma’s viscosity. However, all of these
observations were conducted where the infrastructure (e.g. electricity and road) was
well-organized. If we can improve the flexibility in measurement location, more
comprehensive search for various lava domes becomes possible. The comprehensive search
will clarify the diversity of lava dome and its formation mechanism. For example, we can
classify the vent structures of monogenetic volcanoes as Yokoyama (2010) has proposed. In
addition, the simultaneous observations for three-dimensional tomography will also be more
easily achieved.
The present muon detector comprised of plastic scintillators and photomultiplier tubes
(PMTs) requires commercial electricity or huge solar panels (at least 1 meter square).
Therefore, the measurement locations have been limited. A more power-effective and light
detector has to be developed for improving the flexibility in measurement location.
For these purposes, MPPC is a feasible silicon device because it is small (< 1cm
cube) and does not need high voltage compared with PMT (70V for MPPC and >
1kV for PMT). If we can build a detector with MPPC, the power consumption
of front-end electronics becomes almost negligible compared with PMT system
(72W for multi-anode PMT and 8W for Cockcroft-Walton PMT). MPPC is also
good at cost compared with PMT (50 USD for MPPC and 1000 USD for PMT per
channel).
However, MPPC has two disadvantages to be overcome. Firstly, MPPC has a
high dark-noise rate (600 kHz for 1 p.e. at T = 30 degrees Celsius). In order to
discriminate muon pulses from dark-noise pulses by using coincidence technique,
more than 15 (on average) muon induced photons have to be captured at MPPC’s
photo-cathode. This will be achieved by increasing the composition of POPOP in the plastic
scintillator and optimizing the coupling of MPPC and a scintillator. Improving of the
light emission efficiency in a plastic scintillator is important also in the case of
PMT detector because this will lead to weight reduction of scintillators used in a
detector. Second problem is that the gain depends on ambient temperature. This
is also solved by changing applied bias voltage according to the air temperature
variation.
In this report, the inspection of MPPC’s performance including dark-noise and
temperature dependence of gain will be explained. The whole design of MPPC muon
counting system will be shown, focusing on the coincidence technique of discriminating
muon pulses from dark-noise pulses. We will address some remarks on our developing
electronics for weight and power reduction. |
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