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1-H - 1 LANL EVAL-FEB98 G.M.HALE, P.G.YOUNG
Ch99 DIST-JAN09 20090105
----JEFF-311 MATERIAL 125
-----INCIDENT NEUTRON DATA
------ENDF-6 FORMAT
*************************** JEFF-3.1.1 *************************
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** Original data taken from: JEFF-3.1 **
** **
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***************************** JEFF-3.1 *************************
** **
** Original data taken from: ENDF/B-VI.8 **
** **
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ENDF/B-VI MOD 5 Revision, Jan. 2001, S.C. Frankle and P.G. Young
(LANL)
The energy of the photon from neutron capture (MT=102) in
File 12 has been updated to 2.2233 MeV.
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ENDF/B-VI MOD 4 Revision, February 1998, G. M. Hale and
P. G. Young (LANL)
This is an update of the ENDF/B-VI evaluation to extend the
incident neutron energy range from 100 to 150 MeV. The elastic
scattering cross section from the R-matrix analysis used for
ENDF/B-VI is matched in the energy region of 26 - 30 MeV to
elastic cross sections from Arndt's phase-shift solution, Vol.40.
Arndt's elastic cross section is used directly in the evaluation
above the matching region to 150 MeV. A smooth extrapolation was
made of MT=102 to 150 MeV.
This new evaluation has a smoother transition across the
matching region than did the previous ENDF/B-VI file, and
corresponds more closely to the recommendation of the EANDC
standards subcommittee for n-p cross sections above 20 MeV.
Proton kerma values calculated from this file deviate by no more
than 2% from the previous ENDF/B-VI values at energies up to 100
MeV.
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ENDF/B-VI MOD 3 Revision, October 1997, P.G. Young (LANL)
The cross section for radiative capture at thermal was
changed to the ENDF/B-V value (from 0.3326 to 0.3320 b), with
appropriate changes at lower energies for 1/v behavior. The
total cross section was slightly decreased to accomodate this
change in radiative capture.
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ENDF/B-VI MOD 2 Revision, July 1991
The only revision was to add to the description of the
ENDF/B-VI evaluation, given below, the comments on the standards
covariances.
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ENDF/B-VI MOD 1 Evaluation, October 1989, G.M. Hale,
D.C. Dodder, E.R. Siciliano, W.B. Wilson (LANL)
This is a completely new evaluation independent of ENDF/B-V,
except as noted below.
Elastic cross sections and angular distributions below 40 MeV
were determined with a new R-Matrix calculation by Hale and
Dodder. This calculation gives the ENDF/B-VI elastic scattering
cross sections for hydrogen below 20 MeV. Also, elastic cross
sections and angular distributions above 20 MeV were calculated
with the npscat code using phase shifts of Arndt by Siciliano and
Wilson.
Angular distributions at 26 MeV agreed well: below this energy
R-Matrix angular distributions were used; at and above 26 MeV
phase shift angular distributions were used.
Elastic cross sections below 26 MeV were taken from the
R-Matrix work; those above 30 MeV were taken from the phase shift
work. Between these energies the elastic cross section was taken
as follows:
E (eV) R-Matrix Phase shift MF3MT2
---------- ---------- ------------- ---------
2.6E+07 0.36345 0.36029 0.36345
2.7E+07 0.34859 0.34811
2.8E+07 0.33488 0.33104 0.33295
2.9E+07 0.32227 0.31891
3.0E+07 0.31080 0.30567 0.30567
These calculated results were merged with available (n,gamma)
data by Wilson. ENDF/B-V (n,gamma) data were used below 20 MeV;
above this energy, an approximation to the data of M. Bosman et
al. [Bo79] was used.
The (n,gamma) was adjusted to agree exactly with Mughabghab
[Mu81] value at thermal (0.3326 b), and lower energies were
modified according to 1/v law (P. Young, 10/17/89). The total
cross section was then summed again to reflect the revised
(n,gamma).
File 2, MT151 resonance parameters were taken from ENDF/B-V.
File 12 and File 14, MT102 are also taken from ENDF/B-V.
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STANDARDS COVARIANCES
Phase 1 reviewers of the ENDF/B-VI standards cross sections have
expressed the concern that the uncertainties resulting from the
combination of R-matrix and simultaneous evaluations might have
led to uncertainties that are too small. As a result, the
Standards Subcommittee produced (at the May, 1990 CSEWG meeting)
a set of expanded covariance estimates for the standard cross
section reactions. These uncertainties are estimates such that
if a modern day experiment were performed on a given standard
cross section using the best techniques, approximately 2/3 of
the results should fall within these expanded uncertainties. The
expanded uncertainties for the n + H-1 total cross section are
as follows:
Energy Range (keV) Estimated Uncertainty (%)
------------------ -------------------------
1.0E-08 - 20000 0.2
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REFERENCES
[Bo79] M. Bosman et al., Phys.Lett. 82B, 212 (1979).
[Ch99] M.B. Chadwick, P.G. Young, G.M. Hale, et al., Los Alamos
National Laboratory report, LA-UR-99-1222 (1999)
[Mu81] S.F. Mughabghab, M. Divadeenam, and N.E. Holden, Neutron
Cross Sections, Vol. 1, Neutron Resonance Parameters and
Thermal Cross Sections (Academic Press, 1981).
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