Zr in ZrH

 zr(zrh)   LANL       EVAL-apr93 MACFARLANE                       
 ref. 3 (1994)        DIST-MAY10                       20100309   
----JENDL-4.0         MATERIAL 58                                 
-----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.          
 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.                       
 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 eigenvectors 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.     
 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.