Measurement of Neutron Flux Spectra by a Multiple Foil Activation Iterative Method and Comparison with Reactor Physics Calculations and Spectrometer Measurements

Calibration of a Bonner sphere spectrometer in quasi-monoenergetic neutron fields of 244 and 387 MeV

“…To characterize these neutron fields in the energy range from 10 MeV to the nominal maximum energies, a TOF measurement was carried out applying liquid organic scintillators NE213 [21]. The low-energy part of the neutron spectra, including a small thermal and an evaporation peak, were accurately determined by the BSS measurements using the MSANDB unfolding code [25,26] and the three calculated response matrices. Additionally, the thermal and epithermal fluence rates were confirmed by GEANT4 calculations inside the TOF tunnel at the measurement position of the BSS.…”

“…MSANDB is a modified version of the SAND-II unfolding code (Spectrum Analysis by Neutron Detectors) [26] allowing to take relative uncertainties of measurements into account. The unfolding procedure itself, as well as the calibration method presented in this work is based on the mathematical expression describing the count rate of each Bonner sphere.…”

“…In contrast, the continuously increasing count rates with increasing sphere diameter indicate large fluence rates of high-energetic neutrons. The count rates shown in figure 4, together with the prescribed response matrices, were used to unfold the corresponding spectral neutron fluence rate distributions using the MSANDB unfolding code [25,26] with a resolution of ten energy bins per decade. For all BSS measurements, as 'a priori' start spectra the 246 and 389 MeV TOF spectra (re-binned) shown in figure 3 were used at neutron energies E>10 MeV, respectively.…”

“…For the calibration of the BSS, the spectral neutron fluence rate distributions were unfolded using the MSANDB unfolding code [25] and the three prescribed response matrices. MSANDB is a modified version of the SAND-II unfolding code (Spectrum Analysis by Neutron Detectors) [26] allowing to take relative uncertainties of measurements into account. The unfolding procedure itself, as well as the calibration method presented in this work is based on the mathematical expression describing the count rate of each Bonner sphere.…”

Neutron Spectrum Measurements at the White Sands Missile Range Fast Burst Reactor (FBR)

“…Timc-of-flight requires many of the considerations mentioned for proton-recoil as well as necessitating a rather large capital expenditure (7). Activation measurements employing neutron sensitive reactions are widely used, however, results from this technique depend somewhat on the particular set of reactions chosen (8). The activation method is generally considered incapable of providing high resolution neutron spectra measurements but is one of the most useful and widespread techniques currently in use for measuring "smoothed" neutron spectra.…”