1-H - 1

  1-H -  1 LANL       EVAL-OCT05 G.M.Hale                         
                      DIST-MAY10                       20080703   
----JENDL-4.0         MATERIAL  125                               
-----INCIDENT NEUTRON DATA                                        
------ENDF-6 FORMAT                                               
08-07  All data were taken from ENDF/B-VII.0.                     
       Compiled by K.Shibata (jaea).                              
         2200m/s Sig (b)        res. integ. (b) [0.5 to 2.0e+7 eV]
 total      20.768                  -                             
 elastic    20.436                  -                             
 capture     0.332                0.1492                          
The new R-matrix analysis of the N-N system on which the ENDF/B-  
VII evaluation for 1H is based differs from the previous one use  
for ENDF/B-VI in several respects. Firstly, the n-p capture       
reaction (MT=102), and its inverse, deuteron photo-               
disintegration, were a part of the analysis, rather than added    
later as before. The analysis used a new method for including     
photon channels in R-matrix theory [1], which gave a better       
description of the E1 transitions, in particular.  The data for   
these reactions are mostly integrated and differential cross      
sections, but some information about polarizations was also       
included.  The thermal capture cross section was taken to be      
332.0 mb, as was the recommendation from preliminary data         
testing. Good agreement was obtained with recent cross-section    
measurements [2,3] by astrophysical groups in the 20-550 keV      
range, as well as with earlier measurements that had been done    
mostly as photo-disintegration experiments at energies below 14   
The new analysis includes several additional measurements of the  
total cross section (MT=1).  The evaluated cross section          
deviates at most by about -0.5% around 10 MeV from that of        
ENDF/B-VI.  The estimated uncertainty of the MT=1 cross section   
is given at 2 MeV steps in the following table:                   
           En             Uncert. (%)                             
            0                0.20                                 
            2                0.22                                 
            4                0.30                                 
            6                0.36                                 
            8                0.44                                 
           10                0.50                                 
           12                0.49                                 
           14                0.46                                 
           16                0.40                                 
           18                0.35                                 
           20                0.30                                 
For n-p scattering (MT=2), new information was included about the 
low-energy cross sections (MF=3) and about the angular            
distributions (MF=4).  A new measurement of the angular           
distribution at 10 MeV [4], plus corrections to earlier data at   
14 MeV, moved the back-angle asymmetry in the 10-14 MeV range to  
values that lie between those obtained for ENDF/B-V and ENDF/B-   
VI.  The addition of the latest value of the thermal coherent     
scattering length [5] had the interesting effect of reducing the  
"zero-energy" scattering cross section somewhat to agree          
perfectly with an earlier measurement by Houk [6], and disagree   
with the later, more precise, value of Dilg [7].  The             
covariances for MT=2 will be added later, but the uncertainties   
on the integrated cross section should be similar to those        
listed above for the total cross section.                         
[1] G. M. Hale and A. S. Johnson, Proc. 17th Int. IUPAP Conf. on  
    Few-Body Problems in Physics, 5-10 June 2003, Durham NC, W.   
    Gloeckle and W. Tornow,  eds., Elsevier B.V., pp. S120-S122   
[2] T. S. Suzuki et al., Astrophys. Lett. 449, L59 (1995).        
[3] Y. Nagai et al., Phys. Rev. C 56, 3173 (1997).                
[4] N. Boukharouba et al., Phys. Rev. C 65, 014004 (2002).        
[5] K. Schoen et al., Phys. Rev. C 67, 044005 (2003).             
[6] T. L. Houk, Phys. Rev. C 3, 1886 (1971).                      
[7] W. Dilg, Phys. Rev. C 11, 103 (1975).