1 - IAEA Nuclear Data Services

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standard for à'fferential energy cross section measurements !7j > in
suoh a way thr;:, the resulting neutron spectra can "be predicted accurately
by sophisticated transport calculations.
In addition to their use for a standardization effort of ir.-pile neutron
spectrometry techniques, these spectra make possible interesting contri­
butions to the improvement of nuclear data for fast reactors.
This is developed in a recent paper (_8j ; the abstract follows :
"The possibility of generating intermediate standard neutron spectra
through partial moderation of the uranium-235 thermal fission spectrum
within a cavity in a conventional thermal column has been investigated.
Multigroup transport calculations on simple spherical arrangements of
source and moderator have shown that a family of veil predictable neutron
spectra can be produced and that fast reactor spectra are sufficiently
well simulated, in the useful energy range.
A highly flexible mock-up of such a system has been realized in a spheri­
cal cavity hollowed out of the protruding end of the graphite thermal
column of the BR1 reaotor.
Preliminary measurements by the activiation technique are compared with
theory.
It is shown that the device can be used as a tool for better assessment
of neutron spectrometry techniques and for accurate integral testing
of basic nuclear data. Attention is finally drawn upon a modified versior
of the spherical shell transmission technique, which will tentatively be
applied to improve multigroup inelastic and capture cross section sets
for some important materials."