Measurement by FIB on the ISS: Two Emissions of Solar Neutrons Detected?
Figure 9
(a) The arrival directions of neutrons, as observed by the FIB sensor during the period 19 : 59 : 43–20 : 16 : 34 UT. Neutrons coming from the Sun (red) are shown separately from the background neutrons (dark green), but those neutrons are actually observed together by the FIB sensor. The number of events recorded during the above period was 364, and for 44, it was difficult to determine the arrival direction due to low energy. A clear peak of neutrons can be identified within the region 0–20 degrees from the solar direction. Meanwhile, the candidates between 20 and 40 degrees may be neutrons from the Sun, induced by n-C scattering and also distributed at a relatively wide angle due to the limited angular resolution of the FIB sensor for the lowest energy neutrons (about 35 MeV). The bump of the background within the region 40–100 degrees from the solar direction corresponds to the background neutrons produced in the material of JEM by galactic cosmic rays. (b) The same data as used in the plot of (a). However the data were normalized by the solid angle. A sharp peak can be recognized for neutrons from the solar direction (red), while the background neutrons distribute in different angles presented by the green curve. The vertical value represents . Total number of events during 20 : 02–20 : 16 UT was 273 and 54 for the background and for the signal respectively.
