H in ZrH
h(zrh) LANL EVAL-apr93 MACFARLANE
ref. 3 (1994) DIST-MAY10 20100309
----JENDL-4.0 MATERIAL 7
-----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 produced at los alamos in 1993 using
the same model as the ga evaluation of 1968 (ref 1). the
leapr module of njoy was used for the calculation, and
the alpha and beta grids were extended slightly. constants
that match the endf/b-vi values were used.
theory
------
the lattice dynamics of zrh were computed from a central
force model. the slightly tetragonal lattice of zrh_2 was
approximated by a face-centered-cubic lattice. four force
constants (mu, gamma, nu, and delta) were introduced describing
respectively the interaction of a zirconium atoms with its
nearest neighbors ( 8 h atoms) and its next nearest neighbors
(12 zr atoms), and the interaction of a hydrogen atom with
its next nearest neighbors (6 h atoms) and its third nearest
atoms (12 h atoms). eigenvalues and eigenvectos of the
dynamical matrix were calculated, and a phonon frequency
spectrum was obtained by means of a root sampling technique.
weighted frequency spectra for hydrogen in zrh were then
obtained by appropriate use of the dynamical matrix
eigenvectors (ref. 2).
the final values of the four force constants were obtained
by fitting both specific heat and neutron data. the
position of an optical peak observed by neutron scattering
techniques to be centered roughly around 0.14 ev determines
the constant mu, while the overall width and shape of this
peak determine nu and delta respectively. existing neutron
data are not sufficiently precise to confirm the structure
predicted in the optical peak by the central force model.
specific heat data were used to determine the force
constant gamma, which primarily determines the upper
limit on the phonon energies associated with acoustic modes.
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. e.l.slaggie, "central force lattice dynamical model for
zirconium hydride", ga-8132 (1967).
3. 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.