International Reactor Dosimetry File 2002 - IAEA Publications

TABLE 4.1. C/E VALUES IN THE CALIFORNIUM-252 NEUTRON FIELD
CALCULATED WITH σ(E) DATA FROM IRDF-90.2, JENDL/D-99 AND
RRDF-98 (cont.)
Reaction
E(50%)
(MeV)
Experiment
C/E
(mb) % IRDF-90.2 JENDL/D-99
RRDF-98
(update)
Mn-55(n,2n)Mn-54 12.84 4.075E-1 2.33 1.181 ± 0.115 1.237 ± 0.111 —
Co-59(n,2n)Co-58 13.06 4.051E-1 2.51 1.044 ± 0.051 1.030 ± 0.045 —
Cu-63(n,2n)Cu-62 13.75 1.844E-1 3.98 1.134 ± 0.068 1.140 ± 0.066 —
F-19(n,2n)F-18 14.02 1.612E-2 3.37 1.065 ± 0.063 1.151 ± 0.070 1.009 ± 0.064
Zr-90(n,2n)Zr-89 14.41 2.210E-1 2.89 1.001 ± 0.061 0.979 ± 0.058 —
Ni-58(n,2n)Ni-57 14.98 8.952E-3 3.57 1.033 ± 0.079 1.004 ± 0.072 —
the accuracy level quoted. Unfortunately, such low uncertainties can also
originate from cross-section evaluations based on least squares principles, if the
cross-correlations between the different experimental data sets or the correlations
between data belonging to the same experiment are neglected or
improperly handled.
The impact of unreliable uncertainty values should not be underestimated;
for example, the response of a number of activation reactions in a
typical neutron field is used in reactor dosimetry to derive the spectral fluence
distribution with unfolding methods. The response of each of the activation
reactions represents a broad resolution experiment with a strong overlap in the
energy response range between the various reactions. Unfolding implicitly
requires that the σ(E) data of the various reactions be consistent within the
uncertainties quoted; if this consistency is not maintained, the derived spectral
fluences will exhibit strong discontinuities that will seriously distort the result
of the unfolding process.
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