Graphite
graphite LANL EVAL-apr93 MACFARLANE
ref. 4 (1994) DIST-MAY10 20100309
----JENDL-4.0 MATERIAL 31
-----THERMAL NEUTRON SCATTERING DATA
------ENDF-6 FORMAT
==================================================================
The data were taken from ENDF/B-VI.8.
==================================================================
temperatures = 296, 400, 500, 600, 700, 800, 1000,
1200, 1600, 2000 deg k.
history
-------
this evaluation was generated at the los alamos national
laboratory (apr 1993) using the leapr code. the physical
model is very similar to the one used at general atomic
in 1969 to produce the original endf/b-iii evaluations
(see ref. 1). tighter grids and extended ranges for alpha
and beta were used. a slightly more detailed calculation
of the coherent inelastic scattering was generated. of
course, the various constants were updated to agree with
the endf/b-vi evaluation of natural carbon.
theory
------
graphite has an hexagonal close-packed crystal structure. the
lattice dynamics is represented using a model with four force
constants (refs.2,3). one force constant is used to describe a
nearest-neighbor central force that binds two hexagonal planes
together, another describes a bond-bending force in an hexagonal
plane, the third is for bond-stretching between nearest neighbors
in a plane, and the fourth corresponds to a restoring force
against bending of the hexagonal plane. the force constants
were evaluated numerically using a very precise fit to the
high and low temperature specific heat and compressibility
of reactor grade graphite. the phonon spectrum was computed
from this model using the root sampling method, and then used
to compute s(alpha,beta). the coherent elastic scattering
cross section was computed using the known lattice
structure and the debye-waller integrals from the lattice
dynamics model.
references
----------
1. j.u.koppel and d.h.houston, reference manual for endf thermal
neutron scattering data, general atomic report ga-8774
revised and reissued as endf-269 by the national nuclear
data center, july 1978.
2. j.a.young, n.f.wilkner, and d.e.parks, nukleonik
band 1, 295(1965).
3. j.a.young and j.u.koppel, j.chem.phys. 42, 357(1965).
4. r.e.macfarlane, new thermal neutron scattering files for
endf/b-vi release 2, los alamos national laboratory report
LA-12639-MS (ENDF-356) March 1994.