A Nuclear Cross Section Data Handbook

value used in calculating the mean free path quoted for each pie-chart are listed;
the sources of these data are discussed in Appendix A. The evaluation information
denotes whether or not the evaluation has photon-production data and/or heating
numbers and furthermore, whether these heating numbers are for —— local or total
heating. This matter is discussed in more detail in section IV. The energy range of
the calculation is also listed under evaluation information. The lower energy bound
is 10- 5 eV for ENDF/B-V evaluations and evaluations from Group T-2. The lower
energy bound for ENDL-85 evaluations is 10- 4 eV. Generally, the upper energy
bound is 20 MeV; exceptions are duly noted. Under reaction information all of
the reactions and their respective ENDF/B MT numbers are listed, along with the
respective kinematic and reaction Q values (described in Appendix A).
There are a few isotopes for which reactions given as discrete inelastic scattering
(51< MT < 90) may not be that. In order to accurately represent energy-angle
correlation of neutron emission spectra from light-element reactions, the cross section
is divided among several inelastic levels. It is this method, sometimes referred
to as the “pseudo-level” technique, in which distinction between kinematic QX and
reaction QR becomes very important. There are notes in Appendix B to describe
these special cases and to explain the repetition of the same reaction label in the
first column under reaction information.
Pie-charts for each evaluation are given at 14 MeV, 1 MeV, and thermal energy.
At these energies the percent contribution of each reaction to the total cross section
is shown graphically and listed numerically, the total cross section in barns and the
mean free path in centimeters are listed; the formula for the mean free path is
A
rnfp(cm) = x (lo24t@n2),
pNACTT
where p is the density (g/cm3 ), A is the atomic weight (g/mole), NA is Avogardo’s
number (=6.023x1023 atm/mole), and OT is the total cross section in barns. The
TOTAL INELASTIC cross section, a;., referred to in the pie charts is the sum of
the cross sections for inelastic-level scattering and the cross section for scattering
to the continuum; viz,
90
Ui~ = E #fT=i
n,n’ + (7:$=91 (2)
;=S1
The graph or plot data of the cross sections for the various reactions consist of a
series of individual curves which characterize the reactions or ENDF/B MT’s for a
given nuclide or isotope. They are grouped into the following eight broad categories-
1. Summarv. Reactions: The total, elastic, absorption, and total fission reactions;
these reactions are always defined over the entire e~erW’ range. 2. Heating Number;
The local or totil heating number in MeV/collision. 3. Gamma Production: The
total photon-production cross section. 4. Fission Reactions: In cases where the total
fission reaction is given as the sum of reactions (n, F)= (n,f) + (n,n’f) + (n,2nf)
+ (n,3nf), the component reactions are given in this plot. 5. Nubar Data The
prompt and total U, the average number of neutrons per fission, are plotted here.
Total Z is labeled MT=452; prompt D is MT=456. In cases where the Z could
4
(1)