TY - JOUR
T1 - Estimation method of planetary fast neutron flux by a Ge gamma-ray spectrometer
AU - Hareyama, M.
AU - Fujibayashi, Y.
AU - Yamashita, Y.
AU - Karouji, Y.
AU - Nagaoka, H.
AU - Kobayashi, S.
AU - Reedy, R. C.
AU - Gasnault, O.
AU - Forni, O.
AU - D'Uston, C.
AU - Kim, K. J.
AU - Hasebe, Nobuyuki
PY - 2016/8/21
Y1 - 2016/8/21
N2 - An intensity map of lunar fast neutrons (LFNs) and their temporal variation has been estimated by fitting "sawtooth" peaks in the energy spectra of lunar gamma rays observed by the Kaguya (SELENE) Gamma Ray Spectrometer (GRS) consisting of a high-purity germanium (HPGe) detector with a BGO scintillator. While an ordinary peak in the spectrum is produced by only gamma ray lines, the sawtooth peak is produced by gamma ray lines and recoil nuclei in the detector by Ge(n, n′ γ) reaction. We develop a model for the shape of the sawtooth peak and apply it to fit sawtooth peaks together with ordinary peaks in actual observed spectra on the Moon. The temporal variation of LFNs is synchronous with that of galactic cosmic rays (GCRs), and the global distribution of fast neutrons on the lunar surface agrees well with the past observation reported by the Neutron Spectrometer aboard Lunar Prospector. Based on these results, a new method is established to estimate the flux of fast neutrons by fitting sawtooth peaks on the gamma ray spectrum observed by the HPGe detector.
AB - An intensity map of lunar fast neutrons (LFNs) and their temporal variation has been estimated by fitting "sawtooth" peaks in the energy spectra of lunar gamma rays observed by the Kaguya (SELENE) Gamma Ray Spectrometer (GRS) consisting of a high-purity germanium (HPGe) detector with a BGO scintillator. While an ordinary peak in the spectrum is produced by only gamma ray lines, the sawtooth peak is produced by gamma ray lines and recoil nuclei in the detector by Ge(n, n′ γ) reaction. We develop a model for the shape of the sawtooth peak and apply it to fit sawtooth peaks together with ordinary peaks in actual observed spectra on the Moon. The temporal variation of LFNs is synchronous with that of galactic cosmic rays (GCRs), and the global distribution of fast neutrons on the lunar surface agrees well with the past observation reported by the Neutron Spectrometer aboard Lunar Prospector. Based on these results, a new method is established to estimate the flux of fast neutrons by fitting sawtooth peaks on the gamma ray spectrum observed by the HPGe detector.
KW - Fast neutron
KW - Gamma ray spectrometer
KW - HPGe detector
KW - Kaguya
KW - Moon
KW - SELENE
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U2 - 10.1016/j.nima.2016.05.045
DO - 10.1016/j.nima.2016.05.045
M3 - Article
AN - SCOPUS:84969849550
SN - 0168-9002
VL - 828
SP - 145
EP - 155
JO - Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
JF - Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
ER -