BeO
beo LANL EVAL-apr93 MACFARLANE
ref. 4 (1994) DIST-MAY10 20100309
----JENDL-4.0 MATERIAL 27
-----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 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 atomics
in 1968 to produce the original endf/b-iii evaluation
(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 evaluations of be and oxygen.
theory
------
beryllium oxide consists of two interpenetrating hexagonal
close-packed structures with four atoms per unit cell. the
lattice dynamics (ref.2) is described using a shell model
whose parameters have been adjusted to fit the elastic
constants, the measured raman frequencies, and preliminary
dispersion relations measured by neutron scattering
(ref.3). only the negative ions are assumed to be
polarizable, and short-range repulsive forces are used for
the first and second neighbors. the frequency spectra
weighted by the squares of the amplitude vectors were
computed separately for beryllium and oxygen and used to
calculate separate scattering laws with gasket. the
scattering laws were then combined and adjusted to be
used with the beryllium free-atom cross section. the
oxygen free-atom cross section has been provided for use
with the short-collision-time approximation (sct). thus,
the thermal cross section computed from either s(alpha,beta)
or by the sct approximation gives an asymptotic limit of
approximately 6.15+3.75 barns. the elastic part of the
scattering was calculated using the average of the debye-waller
factors for beryllium and oxygen.
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. g.borgonovi, lattice dynamics and neutron scattering of beo,
general atomic report ga-8758 (1968).
3. r.m.brugger, k.a.strong, and j.m.carpenter, j.phys.chem.
solids 28, 249 (1967).
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.