International Reactor Dosimetry File 2002 - IAEA Publications

covariance file is folded with the neutron spectrum to obtain the cross-section
contribution to the uncertainty. All acceptable measurement data must include
a measurement uncertainty. Great care must be taken in combining the experimental
data in a statistically valid manner while addressing the issue of
discrepant data [7.3]. Criteria for identifying and rejecting discrepant data must
be established prior to establishing the recommended experimental value.
The uncertainty in the representation of the neutron spectrum within the
standard and reference fields must be taken into account when comparing
measurements with calculated quantities, in which the comparison quantity of
interest is the calculated to experimental ratio (C/E). Sources of uncertainty in
both the calculated and the measured quantities should be combined to
provide an uncertainty in the C/E ratio, and the result should always be
reported as the C/E ratio together with the number of standard deviations.
Note that the validation procedure for library selection using reference
neutron fields did not result in any changes in the selected cross-sections.
However, this process did serve to identify those values where either the crosssection
or the reference field characterization should be further examined.
Even if not required to have only one standard field in a given energy region,
the reference neutron fields have neutron spectrum characterizations that were
derived from activation foils in conjunction with spectrum unfold or
adjustment methods. Since this spectrum characterization process introduces
correlations between the spectrum and the cross-section evaluations that are
not taken into account in the least squares spectrum adjustment, these data
cannot be used in the cross-section selection process, only in the validation
process.
7.1. DESCRIPTION OF SELECTED REFERENCE NEUTRON FIELDS
IRDF-2002 consistency tests were performed over as many reference
neutron fields as possible in order to obtain the most extensive validation. The
reference neutron fields that are considered are those for which there exist
published activation foil measurement data for a large set of the important
dosimetry reactions, supported by published and peer reviewed neutron
spectrum characterizations. Fields considered include those listed in Table 7.1.
Unfortunately, due to time constraints and difficulties in obtaining details
on the neutron spectrum characterization for the reference neutron fields, only
two fields were included in this initial validation for IRDF-2002. The problem
with many potential fields that had reported activation data was that the field
neutron spectrum uncertainty and covariance matrix were not available to the
authors of this report. Hopefully, as more detail is acquired on other reference
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