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.          
 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.                      
 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.                                
 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.