Fission Product Yield Data for the Transmutation of Minor Actinide ...

therefore his benchmark calculations do not agree
in the intercomparison with the unadjusted
experimental data, nor with the other calculations.
5.1.3.2. Five Gaussian systematics for fission
product mass yields (J. Katakura)
Prior to the CRP, Moriyama–Ohnishi
systematics [5.5] was used in Japan to calculate
fission yields. However, as originally formulated,
this approach failed to reproduce more recent
measurements, especially for high energy neutron
and proton induced fission. Using the basic
structure of the systematics, the parameters were
adapted to more recent data.
Mass distributions are described by five
Gaussians in the newly developed systematics.
Heavy asymmetric components are assumed to be
related to the light components by reflection about
a symmetry axis chosen as (AF – (v – ))/2, where AF is
the mass of the target plus projectile system, and v – is
the average number of post-scission neutron
emissions This relationship reduces the number of
independent Gaussians to three. However, the
assumption of reflection symmetry is incorrect at
higher energies (see Section 1.3.4.2).
The five Gaussians were fitted to the experimental
data to obtain global systematics, and the
functional dependences of the parameters on
fissioning nuclides and incident particle energy were
derived. An expression developed by Wahl for this
CRP (see below) was used to determine the energy
dependent v – values. Only post-neutron emission
mass distributions were calculated.
5.1.3.3. Systematics of fission product yields
(A.C. Wahl)
Systematics of fission product yields were
derived in two successive stages:
(1) Gaussian functions were fitted by least
squares methods to experimental data for
each fission reaction;
(2) Resulting Gaussian parameters were fitted to
the corresponding values for U-235T by
equations containing differences between the
fissioning nuclides and excitation energies.
Two energy ranges were defined:
(1) Low energy fission of ≤8 MeV;
(2) High energy fission of ≥20 MeV;
and both ranges from 8 to 20 MeV to obtain a
smooth transition.
Fission yields were assumed to be
independent of composite nuclei formation.
Emissive fission was accounted for by determination
of an ‘average loss’ of mass number and
atomic number from yield calculations, but the
excitation energy of the composite nucleus had to
be maintained as a parameter.
Experimental mass distributions were fitted
with either three (above 20 MeV), five (at low
energies) or even seven (for some targets at very
low energies and for spontaneous fission) Gaussian
functions. As with the systematics of Katakura,
reflection symmetry in the shape of the distribution
was assumed and the symmetry point was calculated
in the same way; only v – was replaced by NT, the
‘average’ total number of neutrons before and after
fission, to account for emissive fission. NT was
derived as a model parameter in the fitting
procedure. The Gaussian parameters determined
for each fission reaction were then fitted by mathematical
functions of the average charge and mass of
the fissioning nuclide and the composite nucleus
excitation energy. These studies also resulted in the
development of a charge distribution, as outlined
briefly at the end of Section 5.1.2.4.
Wahl also evaluated the average numbers of
total neutrons and neutrons emitted by fragments,
and developed a model and systematics for the
energy dependence. These data have been used by
other CRP participants for their systematics.
5.1.3.4. Phenomenological model for fragment
mass and charge distribution in actinide
nuclei fission (Yu.V. Kibkalo et al.)
The phenomenological model of Kibkalo et
al. was originally developed to study the
dependence of the fissioning nucleus formation
cross-section and the fission fragment mass and
energy distributions on the excitation energy and
total angular momentum. A detailed analysis of
the dependence of experimental yield distributions
on actinide nuclei fission has shown, at the time of
formation of the angular mass and energy distributions
of fission fragments, that an essential role is
played by the spectrum of transition states above
the fission barrier, as characterized by their
excitation energy and the total angular
momentum. This work was conducted because
only a few studies were devoted to the influence of
the total angular momentum on fission fragment
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