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The anisotropic emission of neutrons from a cylindrical X1 252Cf source with the spherical external casing was experimentally determined. The influence of metal materials and shapes of the external casing to the anisotropy factor, FI(θ), was assessed by the Monte Carlo calculation, before performing the measurement. The results of the calculation implied that light- and spherical-shaped external casing decreases the anisotropic emission of neutrons from a cylindrical source and the nature of the material does not affect the anisotropic emission to a large extent. The experimental results obtained when a spherical-shaped aluminum protection case was employed also revealed that the anisotropy factor was close to 1.0 with a wide zenith angle range. Considering the source handling and measures against mechanical impact to the source, we designed an SUS304-made spherical protection case for a renovated source delivering apparatus. With the SUS304-made spherical protection case, the measured anisotropy factor FI(90) was determined to be 1.002 ± 0.002 (k = 1). Results from the experiments also indicated that the measured anisotropy factor has a flat distribution from 55 to 125° with zenith angle.

In this study, we developed a 45 MeV neutron fluence rate standard of Japan. Quasi-monoenergetic neutrons with a peak energy of 45 MeV in the neutron standard field were produced by the 7Li(p,n)7Be...

Background: The moderated neutron calibration fields using 241Am-Be sources and a graphite moderator have been constructed at the Facility of Radiation Standard (FRS) in the Japan Atomic Energy Agency (JAEA). Materials and Methods: The neutron spectra of the fields were evaluated by the Monte-Carlo calculations and measurements using the Bonner Multi-sphere Spectrometer. Results and Discussion: The fields have continuous neutron spectra from several MeV to thermal neutron energy, with fluence-averaged energies of 0.84 MeV and 0.60 MeV. Reference values of fluence rates and ambient/personal dose equivalent rates were determined from neutron spectra by measurements. Conclusion: Currently, the fields are available for calibration or performance test of neutron measuring instruments.

A quasi-monoenergetic neutron field generated in the ${^7{\rm Li}({\rm p}, {\rm n})}$ reaction consists of a high-energy monoenergetic peak and a continuum to the low-energy region. In this study, the spectral fluence of the continuum was measured with the time-of-flight (TOF) method using a ${^6{\rm Li}}$ -glass scintillation detector and an organic liquid scintillation detector for the keV and MeV region, respectively. The neutron spectral fluence was determined down to the keV region by implementing a new beam chopping system and the results showed that the neutrons that came directly from the target had a lower energy limit about 100 keV. Discussions were made also on the effect of the time-independent neutrons which are assumed to be room-scattered neutrons. The obtained information is expected to contribute to understanding the quasi-monoenergetic high-energy neutron field and improvements of calibrating neutron detectors in the field.

This article describes the characterization of an in-house developed multi-cylindrical moderator neutron spectrometer, which consists of a cylindrical 3He proportional counter and cylindrical moderator shells of different sizes. The response matrix of the spectrometer was calculated by Monte Carlo simulations for neutron energies from 1 × 10−8 to 10 MeV and verified with measurements in 0.144 MeV, 1.2 MeV and 241AmBe neutron standard fields. Influence of scattered neutrons was properly eliminated from the measured response using the shadow cone technique. The calculated and measured responses were in good agreement in most cases. Differences were

The spectral neutron fluence was measured by a combination of the TOF method (above keV region) and the Bonner unfolding method (whole energy region), for a 45-MeV quasi-monoenergetic high-energy neutron field. The extrapolated TOF-based spectrum information was used as a default spectrum for the Bonner unfolding method. The Bonner measurements were performed using the 3He-counter based Bonner sphere spectrometer (BSS) and the gold-activation BSS. While both unfolding reproduced reasonable solutions, difference in amount of the low-energy neutrons was observed between the types of BSS.