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A quasi-monoenergetic high-energy neutron field produced via 7Li(p,n) reaction consists of a high-energy peak and a continuum down to the low-energy region. The continuum is a background for the measurement for the peak neutrons. Spectral information is necessary to estimate the effect of it. Using a new beam chopping system, the spectral neutron fluence above ∼150 keV was measured by the TOF method. The lower-energy neutrons are time-independent and the unfolding method using the Bonner sphere spectrometer (BSS) is suitable to measure them. However, the common BSS with a 3He or BF3 proportional counter has difficulties in this case: signals caused by high-energy-charged particle are mixed in with the genuine signals caused by thermalized neutrons and the dead-time corrections are difficult in experiments with the pulsed-neutron beam. The gold foil is therefore adopted as a detector element for the BSS. Response matrix of the gold-activation BSS is evaluated by Monte Carlo calculations and response calibrations at a neutron standard facility of the AIST. Measurements for the quasi-monoenergetic high-energy neutron field was performed at the AVF cyclotron facility of TIARA, at the peak neutron energy of 45 MeV.

A spherical neutron counter for spectroscopy and dosimetry has been developed. The counter consists of a spherical polyethylene moderator and three slender /sup 3/He position-sensitive proportional counters. Rough measurements of neutron fluence spectra and ambient dose equivalents, H*(10), have been done in the moderated-neutron field of JAERI. Characteristics of the counter are examined and compared with those of a Bonner sphere neutron spectrometer.

A quasi-monoenergetic neutron field generated in the 7Li(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.