International Reactor Dosimetry File 2002 - IAEA Publications

The rigorous inclusion of all uncertainty components contributing to the
C/E values allows quantitative statements to be made on the quality of the
evaluated σ(E) data, which are valid for the energy response range of the
reaction. Calculated C/E values that show agreement with unity within the
given uncertainties are printed in bold type in Table 4.1; these data show an
optimum agreement between the integral and differential data. C/E values
were also accepted that were within ±5% of unity, even if the calculated uncertainties
were too small to achieve the desired overlap; these values are printed
in normal font in Table 4.1. For most of the investigated reactions, a suitable
data set of σ(E) is identified in one of the libraries under study. This statement
is only invalid for the 199 Hg(n,n′), 24 Mg(n,p), 127 I(n,2n), 55 Mn(n,2n) and
63 Cu(n,2n) reactions.
Table 4.2 contains a summary of the results obtained with selected data
sets of the ENDF/B-VI and JEFF-3.0 libraries. The structure of the table is
identical to that of Table 4.1.
The energy response of the various reactions depends strongly upon the
threshold and shape of the σ(E) data. This response range covers 90% of the
total response of a reaction in the 252 Cf neutron field, and is between 0.21 and
5.70 MeV for the 235 U(n,f) reaction and between 13.12 and 18.25 MeV for the
58 Ni(n,2n) 57 Ni reaction, with mean values E(50%) of 1.70 and 14.98 MeV,
respectively. Thus the C/E values in Tables 4.1 and 4.2 cover quite different
energy regions and provide data only for selected portions of the cross-section
curve. A complete proof of the validity of a cross-section requires additional
investigation of the remaining energy regions.
Additional details of the data analysis are given in Tables 4.3–4.6. A
complete list of considered reactions and all calculated spectrum averaged data
are given for each of the investigated cross-section libraries, independent of the
availability of appropriate experimental data. Column 4 lists numerical values
for the calculated spectrum averaged cross-sections, while the corresponding
uncertainties are found in column 5, and the individual uncertainty contributions
of the σ(E) data and spectral distribution N(E) to the calculated values
are given separately in columns 6 and 7. The original uncertainties of the σ(E)
data are often further reduced by application of the averaging process in the
calculation of spectrum averaged data.
Very low uncertainties are found in column 6 of the tables for a number of
reactions, indicating that the quoted uncertainties of the evaluated σ(E) data
are probably extremely small. An analysis of the covariance files for these
evaluations gives uncertainty values that often approach the accuracy level of
the best known reference cross-sections. When considering the experimental
database of the individual reactions and the spread of the available data, only a
minority of the evaluated data sets with uncertainty values of