Measurement of Atmospheric Neutron and Photon Energy Spectra at Aviation Altitudes using a Phoswich-Type Neutron Detector

Abstract

Neutron energy spectrum from 7 to 180 MeV and photon energy spectrum from 4 to 50 MeV were measured onboard an aircraft using a newly developed phoswich-type neutron detector at 10.8 km altitude (atmospheric depth of 249 g/cm 2 ) and geographical latitude of 39 N (a vertical cut-off rigidity of 10.2 GV) near Japan on February 13, 2008 (at a heliocentric potential of 312 MV). Our results were compared with other measurements obtained using 3 He-loaded or extended-energy multi moderator neutron spectrometers (Bonner balls) at aviation altitudes, an organic liquid scintillator on the ground, and a double-scatter neutron telescope at the top of the atmosphere and with calculations using the LUIN2000, EXPACS and RMC codes. Our measured results give a large, sharp peak around a neutron energy of 70 MeV, although Bonner balls present a broad peak around 100 MeV due to low energy resolution. Our neutron fluxes agree well with the others. The measured photon energy spectrum is between the LUIN2000-and EXPACS-calculated spectra and agrees with measured vertical photon spectra at the top of the atmosphere. This onboard study provides the first experimental neutron energy spectrum in the high-energy region (over 10 MeV) with a high energy resolution.

Digital neutron/gamma discrimination with an organic scintillator at energies between 1 MeV and 100 MeV

“…The implementation of the same algorithm for PSD across a wide energy range is a necessary prerequisite for the application of digital PSD in a detector system which may be employed to measure secondary neutrons from cosmic ray interactions or at accelerator facilities, for example, where the energy spectrum features prominent enhancements both at low energy and around 100 MeV [16]. …”