Some comments on resolution and the analysis and interpretation of experimental results from differential neutron measurements Page: 5 of 32
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I. INTRODUCTORY REMARKS
The development of various nuclear-energy technologies has resulted in.,
a broad range of needs and increasingly stringent accuracy requirements for
nuclear data upon which these technologies are founded, for example, accu-
racies of ~2-55! for the fast-breeder reactor dosimetry differential cross
section data base have been established as program objectives. At present,
experimental techniques are not quite up to meeting that requirement and a
near-term goal of ~4-7% seems more realistic except for a few special cases. »
Accuracy goals of ~l-3/S hav| been established for certain key actinide cross
sections such as °U(n,f). This objective has not been achieved either.
Considerable attention is now being devoted to such matcers as neutron
flux measurement, standard cross sections, improved knowledge of nuclear
decay schemes, conversion parameters, etc. This effort is necessary, but
not sufficient. It is now well known that many neutron cross sections which
are important for nuclear technology fluctuate dramatically with energy and
angle. For some applications, only the average behavior is of importance.
For others, the implications of this structure are profound (e.g. shielding).
In the past decade, improved experimental resolution has revealed significant
structure up into the MeV-energy range, especially for medium mass elements
(A = 20-70) which are used as coolants or in structural components of nuclear-
energy devices. An important point which is often overlooked is that the
existence of structure in the microscopic cross sections can seriously hamper
attempts to accurately measure those cross sections (e.g. Ref. 4). In cases
where the cross sections exhibit a great deal of structure, differences in
the results of various measurements may be due in large part to structural
effects rather than to difficulties in measuring neutron fluence or to incon-
sistencies in the use of other nuclear parameters required for the experiments.
Figure i is an example which demonstrates the gravity of this problem. This
figure indicates the confusion which is introduced by attempting to compare
the results of various measurements of a given cross section without regard
to the effects of structure on the experimental process.
There are problems which may never be entirely resolved. Precise,
detailed comparison of the results of measurements of fluctuating cross
sections may not be possible unless experimenters acquire and report more
information about their work than appears to be practical. In fact, the
volume of information which is now being generated is severely straining
the procedures and institutions which have traditionally been used to
exchange scientific results (reports, journals, data center files, etc.).
However, it is suggested that considerable improvement beyond the present
state of affairs is possible without drastic modification of current experi-
mental and comraunicational practices. If the accuracies which are now
being sought for the nuclear data underlying various technologies are to be
achieved, it will be necessary for scientists to agree upon the definitions
of and relationships between various experimental quantities normally used
to express the results of their work. Furthermore, it will be necessary
for investigators to analyze the results of their measurements in terms of
the parameters of their specific experiments to a greater extent than has
been the practice heretofore. This is not an unreasonable expectation
since much of the requisite analytical work can be performed using digital
computers. Of course, there is the additional responsibility of having to
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Smith, D.L. Some comments on resolution and the analysis and interpretation of experimental results from differential neutron measurements, report, November 1, 1979; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc1092970/m1/5/: accessed April 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.