Cross-Section Measurements in the Intermediate-Energy Standard Neutron Field

G.P. Lamaze, C.M. Eisenhauer, J.A. Grundl, E.D. McGarry, F.J. Schima, and V. Spiegel

National Bureau of Standards, Gaithersburg, MD, 20899, USA

Spectrum-averaged cross sections of six reactions of interest to neutron dosimetry have been measured in the Intermediate Energy Standard Neutron Field (ISNF) at the National Bureau of Standards (NBS). The ISNF neutron energy spectrum resembles a fast reactor spectrum, but has a much less complex structure due to the simplicity of its spherical configuration. The median energy is about 0.58 MeV, with 98% of the neutron fluence between 1.2 keV and 5.6 MeV. The ISNF neutron fluence is determined by fluence transfer from a calibrated 252Cf fission source. Samples of 235U were irradiated to a known fluence in compensated beam geometry in the 252Cf field and the 140Ba-140La count rate determined with a high purity germanium detector. Similar 235U samples were then irradiated in the ISNF as a fluence monitor and counted in the identical geometry. The following spectrum-averaged cross sections were obtained: 23Na(n,γ)24Na = 1.57 ± .10 mb, 45Sc(n,γ)46Sc = 24.4 ± 0.8 mb, 59Co(n,γ)60Co = 36.3 ± 1.5 mb, 109Ag(n,γ)110mAg = 23.8 ± 0.9 mb, 115In(n,n')115mIn = 97.0 ± 2.5 mb, and 197Au(n,γ)198Au = 411 ± 11 mb. Comparisons with calculated spectrum-averaged cross-sections are presented.

KEYWORDS: fast neutrons, cross section, 115In(n,n')115mIn, 197Au(n,γ)198Au, 23Na(n,γ)24Na, 59Co(n,γ)60Co, 109Ag(n,γ)110mAg, 45Sc(n,γ)46Sc