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1-H - 2 LANL EVAL-FEB97 P.G.YOUNG,G.M.HALE,M.B.CHADWICK
Ch97,Ch99 DIST-JAN09 20090105
----JEFF-311 MATERIAL 128 REVISION 3
-----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 *************************
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** Original data taken from: ENDF/B-VI.8 **
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ENDF/B-VI MOD 4 Evaluation, February 1997, M.B. Chadwick,
P.G. Young, and G. M. Hale (LANL)
Produced with FKK/GNASH/GSCAN code in cooperation with ECN Petten
SUMMARY
This evaluation provides a complete representation of the
nuclear data needed for transport, damage, heating,
radioactivity, and shielding applications over the incident
neutron energy range from 1.0E-11 to 150 MeV. Below 50 MeV the
evaluation is based mainly on the ENDF/B-VI.3 (Release 3)
evaluation by Young (Yo94).
To summarize, the following ENDF sections are utilized at all
energies:
MF=3 MT= 1 Total Cross Section
MT= 2 Elastic Scattering Cross Section
MT= 3 Nonelastic Cross Section
MT= 16 2H(n,2n)1H Cross Section
MT=102 Radiative Capture Cross Section (Estimate Only at
higher energies)
MF=4 MT= 2 Elastic Angular Distributions
MF=6 MT= 16 Production Cross Sections and Energy-Angle
Distributions for Emission Neutrons, Protons,
Deuterons, and Alphas; and Angle-Integrated
Spectra for Gamma Rays and Residual Nuclei That
Are Stable Against Particle Emission
The following modifications were made to the ENDF/B-VI.3
evaluation:
1. The (n,2n), elastic, and nonelastic cross sections were
revised slightly above 10 MeV to better reflect experimental
data;
2. The tabulated elastic scattering angular distributions
(MF=4, MT=2) below 3.2 MeV and above 20 MeV were revised
slightly to better reflect measurements. The results below 3.2
MeV are based on a couple-channels R-matrix analysis.
METHODOLOGY USED IN NEW EVALUATION
The neutron total cross section is based on ENDF/B-VI below
100 MeV and on experimental data between 100 and 200 MeV. The
elastic scattering, nonelastic, and 2H(n,2n)1H cross sections
were determined above 10 MeV in concert, using the fact that the
nonelastic cross section essentially equals the (n,2n) cross
section above En ~ 1 keV, and the elastic and nonelastic cross
sections must sum to the total cross section. Note that we
revised the existing ENDF/B-VI (n,2n) cross section at most
energies between 10 and 100 MeV to improve the agreement with
experimental data. We also included experimental data for the
proton reaction cross section of 2H in our analysis, as we
determined empirically that it is entirely consistent with the
neutron nonelastic (or reaction) cross section above an incident
nucleon energy of about 20 MeV.
The elastic cross section and angular distributions below an
incident energy of 4 MeV were validated by comparing to results
of a coupled-channels R-matrix analysis. No changes were made
to the existing ENDF/B-VI.2 cross section evaluation because the
results were consistent with data and the R-matrix analysis;
the elastic angular distributions below 3.2 MeV were replaced
with tabulated distributions from the R-matrix analysis.
Several elastic scattering angular distribution measurements
exist above 20 MeV which we fit with Legendre expansions to get
integrated cross sections and to establish the evaluated angular
distributions. Especially important are the measurements of
Romero, Wang, and Howard, as well as the partial distributions
of Yountz and Palmieri. We inferred nonelastic cross sections
from the elastic scattering angular distribution measurements
above 20 MeV, combined with our evaluated total cross section
from experimental data.
We assume that the energy distributions of neutrons from
2H(n,2n)1H follow a pure three-body phase space distribution at
all incident neutron energies and utilize LAW=6 in MF=6 to
represent these energy distributions.
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REFERENCES
[Ch97]. M.B. Chadwick, P G. Young, and G. M. Hale, "Evaluation
of n + 2H Cross Sections," Group T-2 Progress Report for the
Accelerator Production of Tritium Program, 1 January - 1
February 1997.
[Ch99] M.B. Chadwick, P.G. Young, G.M. Hale, et al., Los Alamos
National Laboratory report, LA-UR-99-1222 (1999)
[Yo94]. P.G. Young, "n + D Evaluation to 100 MeV," Release 3,
ENDF/B-VI evaluation, distributed April, 1995.
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ENDF/B-VI MOD 3 Revision, November 1996, P.G.Young (LANL)
File 6, MT=16: Second subsection added.
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ENDF/B-VI MOD 2 Evaluation, March 1994, M.B. Chadwick,
P.G. Young, and G.M. Hale (LANL)
This evaluation is a revision of the ENDF/B-VI evaluation
by Stewart and Horsley (LA-3271, 1968). The evaluation was
extended to 100 MeV based on experimental total, elastic, and
(n,2n) cross section measurements and elastic scattering
angular distribution measurements. Additionally, the total
cross section (and elastic cross section) were revised between
3 and 8 MeV on the basis of newer data, and similarly the (n,2n)
cross section was revised above 10 MeV.
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ENDF/B-VI MOD 1 Evaluation, December 1989, R.E. MacFarlane (LANL)
CONVERTED FOR ENDF/B-VI AT LOS ALAMOS NATIONAL LABORATORY.
THE CROSS SECTIONS, ELASTIC MF4, AND PHOTON PRODUCTION
DATA WERE LEFT UNCHANGED. MF4 AND MF5 FOR THE (N,2N)
REACTION WERE REMOVED AND REPLACED BY AN MF6 USING AN
ANALYTIC PHASE-SPACE REPRESENTATION. THIS IS CONSISTANT
WITH THE ORIGINAL EVALUATION, BUT PROVIDES A MORE
ACCURATE REPRESENTATION OF THE ENERGY-ANGLE CORRELATION
OF (N,2N) NEUTRONS.
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MF=2 NO RESONANCE PARAMETERS GIVEN
MF=3
MT=1
TOTAL CROSS SECTIONS. ALL DATA PLOTTED AND COMPARED UP TO
1967 IN LA-3271. CHANGES INCORPORATED BELOW 1.5 MEV BUT
EVALUATION DOES NOT AGREE WITH LOW-ENERGY EXPERIMENTS AT
NBS (WHICH ARE PRELIMINARY) BUT AGREES AT HIGHER ENERGIES.
THE DAVIS DATA SHOW A PECULIAR DROP OF A FEW PERCENT FROM
3.5 TO 9 MEV BUT AGREE ABOVE AND BELOW THESE ENERGIES.
MT=2
ELASTIC CROSS SECTIONS. DATA OBTAINED FROM INTEGRATING N-D
AND P-D ANGULAR DISTRIBUTIONS. SINCE THE RADIATIVE
CAPTURE IS IN MICROBARNS, THE ELASTIC IS ESSENTIALLY
EQUAL TO THE TOTAL CROSS SECTION BELOW THE N,2N
THRESHOLD AND THE TOTAL MINUS THE N,2N ABOVE THE
THRESHOLD. CHECKS AND BALANCES WERE ALWAYS MADE. SEE
LA-3271 FOR THE GRAPHICAL COMPARISONS.
MT=16
N,2N CROSS SECTION. DATA TAKEN FROM HOLMBERG AND FROM
CATRON. SEE LA-3271. NOTHING IS KNOWN ABOUT THE CROSS
SECTION ABOVE 14 MEV.
MT=102
RADIATIVE CAPTURE CROSS SECTION. THE THERMAL CROSS SECTION
IS 506 MICROBARNS WHICH WAS EXTRAPOLATED AS 1/V UP TO
1 KEV. CURVE WAS DRAWN ABOVE THIS ENERGY TO INCLUDE
MEASUREMENTS ON THE INVERSE REACTION BY BOSCH. THE
14 MEV VALUE IS A FACTOR OF 3 LOWER THAN CERINEO.
SEE LA-3271 FOR GRAPHICAL RESULTS.
MF=4
MT=2
ELASTIC ANGULAR DISTRIBUTIONS TAKEN FROM N-D AND P-D SCAT.
AGREEMENT IS GOOD WITH VAN OERS ANALYSIS. SEE LA-3271.
MF=6
MT=16
ENERGY-ANGLE DISTRIBUTIONS REPRESENTED AS A
3-BODY PHASE SPACE DISTRIBUTION.
MF= 8 AND 9
MT=102 DECAY INFORMATION ADDED FOR TRITIUM PRODUCTION
MF=12 AND MF=14
MT=102
ASSUMED A SINGLE GAMMA EMITTED AT ALL ENERGIES.
EMPLOYED THE LP = 2 FLAG TO CONSERVE ENERGY
FOR REFERENCES, SEE LA-3271.
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