1-H - 1 LANL EVAL-JUL16 G.M.Hale NDS 148, 1 (2018) DIST-DEC21 20170124 ----JENDL-5 MATERIAL 125 -----INCIDENT NEUTRON DATA ------ENDF-6 FORMAT HISTORY 20-09 All data were taken from ENDF/B-VIII.0. 21-11 revised by O.Iwamoto (MF8/MT102) added 21-11 above 20 MeV, JENDL-4.0/HE merged by O.Iwamoto **************************************************************** 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 MeV. 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. REFERENCES [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 (2004). [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). **************************************************************** Covariances were adopted from COMMARA-2.0 library in July 2011. These covariances were obtained at LANL by full scale R-matrix analysis of more than 5000 experimental data (chi-square/degree of freedom of 0.83). [1] The major channel in this case is elastic scattering, often labeled also as ''n-p'' scattering. Elastic scattering serves as neutron cross section standard from 1 keV to 20 MeV, with cross sections well determined. Uncertainties for elastic scattering rise from values well below 1%, reach maximum at about 8 MeV, then gradually decrease with increasing energy. In addition to elastic scattering, covariances are supplied for radiative capture. REFERENCES [1] G. M. Hale, "Covariances from light-element R-matrix analyses," Nuclear Data Sheets, 109, 2812 (2008). ****************************************************************