K. Koga, T. Goka, H. Matsumoto, T. Obara, O. Okudaira, S. Shibata, T. Yamamoto, Y. Muraki
A new type of solar neutron detector (FIB) was launched onboard the Space Shuttle Endeavour on July 16, 2009, and it began collecting data at the International Space Station (ISS) on August 25, 2009. This paper summarizes the observations obtained by the FIB until the end of July 2012. The FIB sensor can determine both the energy and arrival direction of neutrons. We measured the energy spectra of background neutrons over the SAA region and other regions, and found the typical trigger rates to be 1.7 Hz and 0.047 Hz, respectively. It is possible to identify solar neutrons under the level of 0.003 Hz, provided that directional information is applied. Solar neutrons were observed in association with the M-class solar flares that occurred on March 7 (M3.7) and June 7 (M2.5) of 2011. This marked the first time that neutrons were observed in M-class solar flares. Together with our data, many interesting reports were prepared on the same flares, including the precipitation of plasma bubbles, long-lasting gamma ray emissions, and observation of the start of a coronal mass ejection (CME). Such new data will certainly provide us with new aspects of solar physics. The FIB detector onboard the ISS had observed three more solar neutron events in association with the solar flare events on Sep. 24, 2011 (M3.0), Nov. 30, 2011 (X1.9), and Jan. 23, 2012 (M8.7).
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http://arxiv.org/abs/1208.0656
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