Time-of-flight measurement of low-energy components of quasi-monoenergetic high-energy neutron field

A quasi-monoenergetic neutron field generated in the
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Li(p,n) reaction consists of a high-energy monoenergetic peak and a continuum to the low-energy region. The continuum is a background for the response measurements of neutron detectors for the high-energy-peak neutrons and the effect of the continuum should be properly considered. A spectral fluence of the continuum is typically measured by time-of-flight (TOF) methods with an organic liquid scintillation detector. The lowest energy of this method is limited to several MeV because of a high repetition rate of proton beams generated by the AVF cyclotron. Recently, a new beam chopping system available at the TIARA AVF cyclotron facility achieved 1/80 reduction of the beam repetition rate and the lower limit energy of the TOF method has decreased to 20 keV. A Li-glass scintillation detector was also used for measurements of keV region, which is below the working range of the organic liquid scintillation detector. The spectral fluence of the quasi-monoenergetic high-energy neutron field measured by the TOF method using the two scintillation detectors is reported in this presentation.