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8-O - 16 LANL EVAL-APR01 HALE,YOUNG,CHADWICK,CARO,LUBITZ
Ch96ab,Ca98,Ch99,Yo01 DIST-JAN09 REV2-NOV07 20090105
----JEFF-311 MATERIAL 825
-----INCIDENT NEUTRON DATA
------ENDF-6 FORMAT
*************************** JEFF-3.1.1 *************************
** **
** Original data taken from: JEFF-3.1 Updated **
** Modification: New MT=800-803 by G. Noguere **
******************************************************************
HISTORY
05-05 Evaluation for JEFF-3.1 is ENDF\B-VI.8
11-07 (n,alpha0) cross section replaced by G. Noguere with
cross section of ENDF\B-VII.0 in accordance with [Gi07]
******************************************************************
ENDF/B-VI MOD 3 Evaluation, April 2001, P.G. Young, G.M. Hale
M.B. Chadwick (LANL), E.Caro, C.R. Lubitz (KAPL)
This evaluation is a combination of a new MOD 3 evaluation
below 30 MeV and the previous MOD 2 evaluation from 20 to 150 MeV.
Both these evaluations are described below. The only change to the
data above 30 MeV is to add tritium-production data, based on
experimental yield data and spectra calculated with the GNASH
Hauser-Feshbach/preequilibrium code.
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. The discussion here is divided into the
region above and below 30 MeV.
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INCIDENT NEUTRON ENERGIES > 30 MeV
The evaluation above 30 MeV utilizes MF=6, MT=5 to represent
all reaction data. Production cross sections and emission
spectra are given for neutrons, protons, deuterons, alpha
particles, gamma rays, and all residual nuclides produced (A>5)
in the reaction chains. To summarize, the ENDF sections with
non-zero data above En = 30 MeV are:
MF=3 MT= 1 Total Cross Section
MT= 2 Elastic Scattering Cross Section
MT= 3 Nonelastic Cross Section
MT= 5 Sum of Binary (n,n') and (n,x) Reactions
MT=102 Radiative Capture Cross Section (Estimate Only)
MF=4 MT= 2 Elastic Angular Distributions
MF=6 MT= 5 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 evaluation is based on nuclear model calculations that
have been benchmarked to experimental data, especially for n +
O16 and p + O16 reactions [Ch96a]. We use the GNASH code system
[Yo92], which utilizes Hauser-Feshbach statistical, preequi-
librium and direct-reaction theories. Coupled-channel and
spherical optical model calculations are used to obtain particle
transmission coefficients for the Hauser-Feshbach calculations,
as well as for the elastic neutron angular distributions.
Cross sections and spectra for producing individual residual
nuclei are included for reactions that exceed a cross section of
approximately 1 nb at any energy. The energy-angle-correlations
for all outgoing particles are based on Kalbach systematics
[Ka88].
A model was developed to calculate the energy distributions of
all recoil nuclei in the GNASH calculations [Ch96b]. The recoil
energy distributions are represented in the laboratory system in
MT=5, MF=6, and are given as isotropic in the lab system. Note
that all other data in MT=5,MF=6 are given in the center-of-mass
system. This method of representation requires a modification of
the original ENDF-6 format.
Preequilibrium corrections were performed in the course of the
GNASH calculations using either Feshbach, Kerman, Koonin (FKK)
theory [Ch93] or the exciton model of Kalbach [Ka77, Ka85].
Discrete level data from nuclear data sheets were matched to
continuum level densities using the formulation of Ignatyuk
[Ig75] and pairing and shell parameters from the Cook [Co67]
analysis. Neutron and charged-particle transmission coefficients
were obtained from the optical potentials, as discussed below.
Gamma-ray transmission coefficients were calculated using the
Kopecky-Uhl model [Ko90].
------------------------------------------------------------------
INCIDENT NEUTRON ENERGIES < 30 MeV
The evaluation below 30 MeV includes complete data for all
significant neutron-induced reactions. It is comprised of
R-parameter [Ca98] and R-matrix analyses below 6.25 MeV, and a
combination of experimental and theoretical data evaluation
from 6.25 to 30 MeV. A summary of the evaluation by energy
range is given below, followed by a detailed description of
the evaluation, reaction by reaction.
NEUTRON ENERGY < 6.25 MeV
The evaluation below 3.4 MeV is an R-function fit [Ca98] to
experimental data. At 3.4 MeV, it is spliced to the LANL R-matrix
analysis with a transition region of about 60 keV centered at
3.4 MeV. The LANL analysis is used for the region from 3.40 to
6.25 MeV.
NEUTRON ENERGY > 6.25 MeV
The following major modifications were made above 6.25 MeV:
1. The maximum energy of the evaluation was increased from 20 to
30 MeV.
2. New measurements of 16O(n,xgamma) angular distributions (7
angles, En = 4 - 200 MeV) by Nelson et al. [Ne99] were incor-
porated into the evaluation. The measurements use a high-
resolution Ge detector and result in data for some 21 gamma rays.
The distributions were fit with Legendre expansions to obtain
angle-integrated cross sections for MF=13 and angular
distributions for MF=14. Nuclear energy level schemes and gamma
branching ratios [Aj86,Aj91] were utilized to extract level
excitation cross sections in MF=3 for discrete states in 16O,
14-16N, and 13C, corresponding to (n,n'), (n,p), (n,d), (n,t),
and (n,alpha) reactions.
3. New measurements of 16O(n,alpha) cross sections at 14 MeV by
Sanami and Baba [Sa97] were used to adjust the (n,alpha) cross
sections.
4. The neutron total cross section measurements of Finlay [Fi93]
were incorporated into the evaluation above 7.3 MeV. Adjustments
of up to 2% were made in the existing evaluation.
5. The new evaluation contains no pseudo level or excitation
energy bin data. Calculations were made with the GNASH code to
provide continuum emission data in MF=6 format, as well as any
unmeasured data. Calculated cross sections were renormalized
whenever possible using experimental data. The GNASH calculations
utilized transmission coefficients calculated with a spherical
optical potential and level densities from the Gilbert and
Cameron model, plus preequilibrium corrections using systematic
values of parameters.
6. Comparisons of the evaluation with a large body of
experimental data have been made to validate the new data.
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DETAILED DESCRIPTION REACTION BY REACTION
MF=2 RESONANCE PARAMETERS -------------------------------------
The evaluation below 3.4 MeV is an R-function fit [Ca98] to
experimental data using an optical model to provide a background
R-function. The procedure is coded in the KAPL code "OPTIC",
with an extension of the original code to convert the optical-
model phase shifts to background R-functions.
The analysis is carried to 3.4 MeV, where it is spliced to the
LANL R-matrix analysis, with a transition region of about 60 keV
centered at 3.4 MeV.
From 3.4 to 6.25 MeV, a test evaluation was obtained from a new
multi-channel R-matrix analysis of a large part of the available
experimental data base using the EDA code. The analysis of the
17O system includes data for n+16O neutron total cross sections
and elastic scattering angular distributions, as well as data
for the 16O(n,alpha) reaction in both the (n,alpha) and
(alpha,n) directions. Also included are excitation functions
for alpha+13C elastic scattering. The total cross sections in
the final version of this analysis may change, especially in the
region above 4 MeV.
Effective scattering radius = 5.56256E-13 cm.
MF=3 NEUTRON CROSS SECTIONS -----------------------------------
THERMAL (2200 m/s) CROSS SECTIONS
TOTAL = 3.89440 B RADIATIVE CAPTURE= 0.1900 MB
ELASTIC= 3.89421 B
MT=1 TOTAL CROSS SECTION
0.0 to 3.40 MeV, calculated from R-function fit to total cross
section and elastic angular distributions - see above.
3.4 to 6.25 MeV, calculated from R-Matrix parameters by
simultaneously fitting most of the available 16O(n,n)16O and
16O(n,alpha0)13C data, as well as 13C(alpha,alpha)13C data at
energies below En = 6.2 MeV. The experimental total cross
section data fitted in the analysis were the [Jo74] results below
6.26 MeV, and the [La80] measurements at higher energies, with
inserts of the high-resolution data of [Jo79] over the resonances
and in the window at En = 2.3-2.4 MeV.
6.25 to 30 MeV, based on an adjustment of the covariance
analysis used for the ENDF/B-VI (Rel. 0) evaluation to
accommodate the new measurements of Finlay et al. [Fi93]. The
previous ENDF/B-VI (Rel. 0) evaluations is based on analysis
with the GLUCS Bayes code [He80] of the remaining major total
cross section measurements [Fo71], [Pe72], [Sc72], [La80],
[Ci68], [Ci80], with structure inserted from the high-resolution
[Ci80] measurement.
MT=2 ELASTIC SCATTERING CROSS SECTION
0.0 to 3.40 MeV, calculated from R-function fit to total cross
section and elastic angular distributions - see above.
3.4 to 6.25 MeV, R-matrix analysis that includes all available
experimental data, as described above. Elastic angular
distribution data used in the analysis includes [La60], [Ok55],
[Fo58], [Ma62], [Fo70], [Hu62], [Ph61], [Jo67], [Ki72], [Ch61],
[Dr76], [Fo64].
6.25 to 20 MeV, obtained by subtracting the nonelastic cross
section (MT=3) from the total cross section (MT=1), although
small adjustments were made to several of the less well
determined reaction cross sections in order to enhance agreement
with the elastic measurements of Borker [Bo89], Glendinning
[Gl82], and Petler [Pe85]. The magnitude of these adjustments
was generally small and was greatest near structure and near
18 MeV.
MT=4 INELASTIC CROSS SECTION
Threshold to 30 MeV, sum of MT=51-57, 91.
MT=51-57 INELASTIC CROSS SECTION TO DISCRETE STATES
Threshold to 30 MeV, the (n,n') cross sections corresponding
to gamma-emitting excited levels of 16O are included in MT=51-57
as follows:
MT=51 Ex= 6.0494 MeV
MT=52 Ex= 6.129893 MeV
MT=53 Ex= 6.9171 MeV
MT=54 Ex= 7.11685 MeV
MT=55 Ex= 8.8719 MeV
MT=56 Ex=10.957 MeV
MT=57 Ex=11.080 MeV
Note that the 16O levels at 9.585, 9.8445, and 10.356 are
omitted because they decay primarily by alpha particle emission
and those data are included in MT=22.
MT=16 (N,2N) CROSS SECTION
Threshold to 30 MeV, based on GNASH calculation, renormalized
down by approximately 30% to improve agreement with measurement
of Brill et al. [Br61].
MT=22 (N,NALPHA) CROSS SECTION
Threshold to 30 MeV, based on GNASH calculation, with
adjustments made to improve agreement with experimental data,
especially data of Bormann et al. [Bo63].
MT=23 (N,N3ALPHA) CROSS SECTION
Threshold to 30 MeV, based on GNASH calculations, adjusted
from 28 to 30 MeV to agree with LA150 data.
MT=28 (N,NP) CROSS SECTION
Threshold to 30 MeV, based on GNASH calculations, adjusted
such that the production cross sections for the 5.2701 and 5.2988
MeV gamma rays are consistent with Nelson et al.[Ne99] data, and
normalization of proton spectra consistent with 27-MeV data of
Subramanian et al. [Su94].
MT=32 (N,ND) CROSS SECTION
Threshold to 30 MeV, based on GNASH calculations, adjusted
such that difference between total and nonelastic cross sections
agrees with elastic cross section measurements.
MT=41 (N,2NP) CROSS SECTION
Threshold to 30 MeV, based on GNASH calculations, adjusted
such that difference between total and nonelastic cross sections
agrees with elastic cross section measurements.
MT=44 (N,N2P) CROSS SECTION
Threshold to 30 MeV, based on GNASH calculations, adjusted
such that difference between total and nonelastic cross sections
agrees with elastic cross section measurements.
MT=45 (N,NPALPHA) CROSS SECTION
Threshold to 30 MeV, based on GNASH calculations, adjusted
such that difference between total and nonelastic cross sections
agrees with elastic cross section measurements.
MT=91 (N,N'CONTINUUM) CROSS SECTION
Threshold to 30 MeV, based on GNASH calculations, adjusted
such that difference between total and nonelastic cross sections
agrees with elastic cross section measurements.
MT=102 (N,GAMMA) CROSS SECTION
0 to 1 MeV,cross section based on experimental data obtained
from E. Jurney [Ju64]; higher energy data is crude estimate.
MT=103 (N,P) CROSS SECTION
Sum of MT=600-603.
MT=104 (N,D) CROSS SECTION
Sum of MT=650-669.
MT=105 (N,T) CROSS SECTION
Sum of MT=700-709,749.
MT=107 (N,ALPHA) CROSS SECTION
Sum of MT=800-803.
MT=108 (N,2ALPHA) CROSS SECTION
Threshold to 30 MeV, based on GNASH calculations, adjusted
such that difference between total and nonelastic cross sections
agrees with elastic cross section measurements.
MT=112 (N,PALPHA) CROSS SECTION
Threshold to 30 MeV, based on GNASH calculations, adjusted
such that difference between total and nonelastic cross sections
agrees with elastic cross section measurements.
MT=600 (N,P) INTEGRATED CROSS SECTION TO 16N GROUND STATE
Threshold to 30 MeV, based on GNASH calculations with some
renormalization (lowered approximately 30%) from comparison of
excited state predictions with Nelson et al. [Ne99]
measurements.
MT=601-603 (N,P) CROSS SECTION TO EXCITED LEVELS OF 16N
Threshold to 30 MeV, the cross sections for the 0.0.297- and
0.3975-MeV levels are inferred from the (n,p gamma) data of
Nelson et al. [Ne99], using the level structure diagram of 16N
by Ajzenberg-Selove [Aj86]. The cross section for the 0.1201-
MeV level is based on GNASH calculations with some
renormalization (lowered ~30%) from comparison of excited state
predictions with Nelson et al. [Ne99] measurements.
MT=650 (N,D) INTEGRATED CROSS SECTION TO 15N GROUND STATE
Threshold to 30 MeV, based on GNASH calculations with some
renormalization from comparison of excited state predictions
with Nelson et al. [Ne99] measurements.
MT=651-669 (N,D) CROSS SECTION TO EXCITED LEVELS OF 15N
Threshold to 30 MeV, the cross sections for the 5.2701- and
5.2988-MeV levels are adjusted based on the (n,xgamma) data of
Nelson et al. [Ne99], using the level structure diagram for 15N
by Ajzenberg-Selove [Aj91]. Cross sections for remaining levels
are based on GNASH calculations with some renormalization from
comparison of excited state predictions with Nelson et al.
[Ne99] measurements and 27-Mev data of Subramanian et al. [Su94].
MT=700 (N,T) INTEGRATED CROSS SECTION TO 14N GROUND STATE
Threshold to 30 MeV, based on GNASH calculations with some
renormalization from comparison of excited state predictions
with Nelson et al. [Ne99] measurements.
MT=701-709 (N,T) CROSS SECTION TO EXCITED LEVELS OF 14N
Threshold to 30 MeV, the cross section for the 2.3128-MeV
levels is inferred from the (n,t gamma) data of Nelson et al.
[Ne99], using the level structure diagram for 16N by Ajzenberg-
Selove [Aj91]. Cross sections for the remaining levels are
based on GNASH calculations with some renormalization from
comparison of excited state predictions with Nelson et al.
[Ne99] measurements.
MT=749 (N,T) CROSS SECTION TO 14N CONTINUUM
Threshold to 30 MeV, based on GNASH calculations with some
renormalization from comparison of excited state predictions
with Nelson et al. [Ne99] measurements and to enhance agreement
of elastic cross section with measured data.
MT=800 (N,ALPHA0) CROSS SECTION TO 13C GROUND STATE
0.0 to 6.2 MeV, based on R-matrix analysis described above
under MT=1. Data of Ba72 were used in the original (alpha,n)
direction, with no changes in energy scale or normalization.
Also included were the low-energy (alpha,n) data of [Ke91] and
[Dr93].
6.2 to 20 MeV, based on data of [Da63],[Da68],[Si68],[Ba73],
and composite of [Mc66b],[Ma68],[Le68] at 14 MeV. Note that the
[Da63] data were renormalized by factor of 1.5 to bring them
into rough agreement with the R-matrix analysis of the [Ba73]
(n,a0) data, together with the total and elastic data in the
analysis. Because the [Da68] experimental data were normalized
to [Da63], the former were also renormalized by the factor of
1.5.
MT=801-803 (N,ALPHA) CROSS SECTION TO EXCITED LEVELS OF 13C
Threshold to 30 MeV, the cross sections of the 3.0894-,
3.6845-, and 3.8538-MeV levels are inferred from the (n,alpha
gamma) data of Nelson et al. [Ne99], using the level structure
diagram of 13C by Ajzenberg-Selove [Aj91].
MF=4 ANGULAR DISTRIBUTIONS ------------------------------------
MT=2 ELASTIC NEUTRON ANGULAR DISTRIBUTIONS
0.0 to 3.4 MeV, calculated from R-function fit (see MF=3,MT=1).
3.4 to 6.2 MeV, calculated from R-matrix fit (see MF=3,MT=1).
Measured angular distributions input to the fit were those of
[Ch61],[Fo58],[Fo70],[Hi58],[Hu62], [Jo67],[Ki72],[La60],[Li66],
[Ma62],[Ph61],[Jo79]. Fits were attempted using new data of
[Sc77], but those measurements were found to have significant
uncertainties, and some discrepancies with other data were noted.
6.2 to 20 MeV, smooth curve through coefficients derived from
fits to elastic data of [Ph61],[Ne72],[Ch61],[Ba63],[Be67],
[Mc66a],[Ki72],[Bu73],[Ne72],[Gl82],[Ba85],[Bo89],[Pe85].
MT=51-57 DISCRETE (N,N') ANGULAR DISTRIBUTIONS
Threshold to 10 MeV, assumed isotropic in center of mass.
Above 10 MeV, based on fits of the 14-MeV data of [Ki72],[Ne72],
[Ba63],[Mc66a],[Ba85],[Me69], and especially [Bo89].
MT=600-603 DISCRETE (N,P) ANGULAR DISTRIBUTIONS
Threshold to 30 MeV, assumed isotropic in center of mass.
MT=650-669 DISCRETE (N,D) ANGULAR DISTRIBUTIONS
Threshold to 30 MeV, assumed isotropic in center of mass.
MT=700-709 DISCRETE (N,T) ANGULAR DISTRIBUTIONS
Threshold to 30 MeV, assumed isotropic in center of mass.
MT=800 DISCRETE(N,ALPHA0) ANGULAR DISTRIBUTIONS
0.0 to 6.2 MeV, calculated from R-Matrix fit (see MF=3,MT=1).
Measured angular distributions input to the fit were
reconstructed from the Legendre coefficients of [Wa57], and
converted to (n,alpha) angular distributions using detailed
balance.
MT=801-803 DISCRETE (N,T) ANGULAR DISTRIBUTIONS
Threshold to 6 MeV,
6 to 30 MeV, assumed isotropic in center of mass.
MF=6 PRODUCT ENERGY-ANGLE DISTRIBUTIONS -----------------------
MT=16 (N,2N) CONTINUUM ENERGY-ANGLE EMISSION DATA
Threshold to 30 MeV, energy-angle correlated energy spectra
are given for neutrons, and isotropic energy spectra are given
for recoiling 15O nuclei. The neutron data were obtained from
the GNASH calculations; the recoil 15O distributions were
calculated with the RECOIL code [Ma83]. The discrete gamma rays
from (n,2ngamma) reactions are given in MF=13 and 14.
MT=22 (N,NALPHA) CONTINUUM ENERGY-ANGLE EMISSION DATA
Threshold to 30 MeV, energy-angle correlated energy spectra
are given for neutrons and alpha particles, and isotropic energy
spectra are given for recoiling 12C nuclei. The neutron and
alpha data were obtained from the GNASH calculations; the recoil
12C distributions were calculated with the RECOIL code [Ma83].
The discrete gamma rays from (n,nalpha gamma) reactions are
given in MF=13 and 14.
MT=28 (N,NP) CONTINUUM ENERGY-ANGLE EMISSION DATA
Threshold to 30 MeV, energy-angle correlated energy spectra
are given for neutrons and protons; isotropic energy spectra are
given for recoiling 15N nuclei; and isotropic energy spectra are
given for emitted continuum gamma rays. The neutron, proton,
and gamma-ray data were obtained from the GNASH calculations;
the recoil 15N distributions were calculated with the RECOIL
code [Ma83].
MT=32 (N,ND) CONTINUUM ENERGY-ANGLE EMISSION DATA
Threshold to 30 MeV, energy-angle correlated energy spectra
are given for neutrons and deuterons; isotropic energy spectra
are given for recoiling 14N nuclei; and isotropic energy spectra
are given for emitted continuum gamma rays. The neutron,
deuteron, and gamma-ray data were obtained from the GNASH
calculations; the recoil 14N distributions were calculated with
the RECOIL code [Ma83].
MT=41 (N,2NP) CONTINUUM ENERGY-ANGLE EMISSION DATA
Threshold to 30 MeV, energy-angle correlated energy spectra
are given for neutrons and protons; isotropic energy spectra are
given for recoiling 14N nuclei; and isotropic energy spectra are
given for emitted continuum gamma rays. The neutron, proton,
and gamma-ray data were obtained from the GNASH calculations;
the recoil 14N distributions were calculated with the RECOIL
code [Ma83].
MT=44 (N,N2P) CONTINUUM ENERGY-ANGLE EMISSION DATA
Threshold to 30 MeV, energy-angle correlated energy spectra
are given for neutrons and protons; isotropic energy spectra are
given for recoiling 14C nuclei; and isotropic energy spectra are
given for emitted continuum gamma rays. The neutron, proton,
and gamma-ray data were obtained from the GNASH calculations;
the recoil 14C distributions were calculated with the RECOIL
code [Ma83].
MT=45 (N,NPALPHA) CONTINUUM ENERGY-ANGLE EMISSION DATA
Threshold to 30 MeV, energy-angle correlated energy spectra
are given for neutrons, protons, and alphas; isotropic energy
spectra are given for recoiling 11B nuclei; and isotropic energy
spectra are given for emitted continuum gamma rays. The
neutron, proton, alpha, and gamma-ray data were obtained from
the GNASH calculations; the recoil 11B distributions were
calculated with the RECOIL code [Ma83].
MT=91 (N,N'CONTINUUM) CONTINUUM ENERGY-ANGLE EMISSION DATA
Threshold to 30 MeV, energy-angle correlated energy spectra
are given for neutrons; isotropic energy spectra are given for
recoiling 16O nuclei; and isotropic energy spectra are given for
emitted continuum gamma rays. The neutron and gamma-ray data
were obtained from the GNASH calculations; the recoil 16O
distributions were calculated with the RECOIL code [Ma83].
MT=108 (N,2ALPHA) CONTINUUM ENERGY-ANGLE EMISSION DATA
Threshold to 30 MeV, energy-angle correlated energy spectra
are given for alphas; isotropic energy spectra are given for
recoiling 9Be nuclei; and isotropic energy spectra are given for
emitted continuum gamma rays. The alpha, and gamma-ray data
were obtained from the GNASH calculations; the recoil 9Be
distributions were calculated with the RECOIL code [Ma83].
MT=112 (N,PALPHA) CONTINUUM ENERGY-ANGLE EMISSION DATA
Threshold to 30 MeV, energy-angle correlated energy spectra
are given for protons, and alphas; isotropic energy spectra are
given for recoiling 12B nuclei; and isotropic energy spectra are
given for emitted continuum gamma rays. The proton, alpha, and
gamma-ray data were obtained from the GNASH calculations; the
recoil 12B distributions were calculated with the RECOIL code
[Ma83].
MT=749 (N,ALPHA) CONTINUUM ENERGY-ANGLE EMISSION DATA
Threshold to 30 MeV, energy-angle correlated energy spectra
are given for alpha particles; isotropic energy spectra are
given for recoiling 13C nuclei; and isotropic energy spectra are
given for emitted continuum gamma rays. The alpha and gamma-ray
data were obtained from the GNASH calculations; the recoil 13C
distributions were calculated with the RECOIL code [Ma83].
MF=12 PHOTON PRODUCTION MULTIPLICITIES ------------------------
MT=102 (N,GAMMA) PHOTON PRODUCTION MULTIPLICITIES
Photon multiplicities for radiative capture are based on
experimental data obtained from Jurney [Ju64].
MF=13 PHOTON PRODUCTION CROSS SECTIONS ------------------------
MT=4 (N,N'GAMMA) PHOTON PRODUCTION CROSS SECTIONS
Threshold to 30 MeV: Based almost entirely on new angular
distribution measurements by Nelson et al. [Ne99], which
utilized a white neutron source and covered the energy range
from threshold to 200 MeV. The measurements were made at 7
angles using high-resolution Ge detectors and resulted in data
for some 23 gamma rays from 7 different reactions. The angular
distributions were fit with Legendre expansions to obtain angle-
integrated cross sections. The fitted cross sections were
smoothed somewhat for this evaluation, although much of the
measured structure was preserved, particularly for the intense
6.129-MeV gamma. The evaluated data for the following gamma
rays are based directly on the measurements:
EG= 2.742 MeV (decay of 8.8719-MeV level of 16O)
EG= 3.839 MeV (decay of 10.957-MeV level of 16O)
EG= 4.950 MeV (decay of 11.080-MeV level of 16O)
EG= 6.130 MeV (decay of 6.130-MeV level of 16O)
EG= 6.917 MeV (decay of 6.917-MeV level of 16O)
EG= 7.117 MeV (decay of 7.117-MeV level of 16O)
The evaluated cross sections for the remaining (n,n') gamma
rays are inferred from these data using the energy level scheme
of Ajzenberg-Selove [Aj86]. Data were also obtained for gamma
rays of energy 1.755 and 1.955 from decay of the 8.8719-MeV
level but the 2.742-MeV gamma was used to determine the level
excitation cross section because it is the most intense.
Similarly, data were obtained on a 4.179-MeV gamma from decay of
the 11.080-MeV level, but the 4.950-MeV gamma is more intense
and was used to determine the level excitation cross section.
The evaluated data were compared to older gamma-ray
measurements by [Be70], [Ne90], [No78], [Ha59], [Di70], [Or70],
[Dr70], [Cl69], [Lu70], [Bu71], [Ny69]. Considering that very
few (e.g., [Be70], [Dr70]) of these measurements are of full
angular distributions, the agreement is reasonable.
MT=16 (N,2NGAMMA) PHOTON PRODUCTION CROSS SECTIONS
Threshold to 30 MeV: The cross section for the 5.2409-MeV
gamma ray was obtained directly from the Nelson et al. [Ne99]
data. The remaining discrete gammas are based on GNASH
calculations, with some renomalization based on the experimental
data.
MT=22 (N,NALPHA GAMMA) PHOTON PRODUCTION CROSS SECTIONS
Threshold to 30 MeV: Only the 4.438-MeV discrete gamma ray
is given and it is based on the Nelson et al. [Ne99] data.
MT=103 (N,PGAMMA) PHOTON PRODUCTION CROSS SECTIONS
Threshold to 30 MeV: The cross sections for the 0.2774- and
0.297-MeV gamma rays are based on the Nelson et al. [Ne99] data.
The 0.3975-MeV gamma is inferred from the 0.2774-MeV gamma data
through the Ajzenberg-Selove level scheme [Aj86] for 16N. The
0.1201-MeV gamma cross section is based partially on GNASH
calculations and partially inferred from the [Ne99] data using
the 16N level scheme.
MT=104 (N,DGAMMA) PHOTON PRODUCTION CROSS SECTIONS
Threshold to 30 MeV: The cross sections for the 5.2701- and
5.2988-MeV gamma rays are based on the Nelson et al. [Ne99]
data. The cross sections for the remaining 60 (n,dg) gamma rays
are based on GNASH calculations and the Ajzenberg-Selove level
scheme [Aj91] for 15N, after renomalization to agree with the
measured 5.2701- and 5.2988-MeV gamma-ray data.
MT=105 (N,TGAMMA) PHOTON PRODUCTION CROSS SECTIONS
Threshold to 30 MeV: The cross section for the 2.313-MeV
gamma ray is based on the Nelson et al. [Ne99] measurement. The
cross sections for the remaining 20 (n,tg) gamma rays are based
on GNASH calculations and the Ajzenberg-Selove level scheme
[Aj91] for 14N, after renomalization to agree with the measured
2.313-MeV gamma-ray data.
MT=107 (N,ALPHA GAMMA) PHOTON PRODUCTION CROSS SECTIONS
Threshold to 30 MeV: The cross sections for the 3.0894-,
3.6845- and 3.8538-MeV gamma rays are based on the Nelson et
al. [Ne99] data. The 0.1693-, 0.5951- and 0.7644-MeV gamma-ray
cross sections are inferred from the above data through the
Ajzenberg-Selove level scheme [Aj91]. Note that the 0.1693-MeV
gamma from decay of the 3.8538-MeV level also was measured, but
the 3.8538-MeV gamma is more intense and was used to determine
the level excitation cross section.
MF=14 PHOTON ANGULAR DISTRIBUTIONS ----------------------------
MT=4 (N,N'GAMMA) PHOTON ANGULAR DISTRIBUTIONS
Anisotropic angular distributions in Legendre polynomial
representation are given for the 1.755-, 2.742-, 6.130-, 6.917-,
and 7.117-MeV gamma rays, obtained by fitting the measurements
of Nelson et al. [Ne99]. Isotropic angular distributions are
assumed for the remaining gamma rays.
MT=16 (N,2NGAMMA) PHOTON ANGULAR DISTRIBUTIONS
An anisotropic angular distribution in Legendre polynomial
representation is given for the 5.2409-MeV gamma ray, obtained
by fitting the measurements of Nelson et al. [Ne99]. Isotropic
angular distributions are assumed for the remaining gamma rays.
MT=22 (N,NALPHA GAMMA) PHOTON ANGULAR DISTRIBUTIONS
An anisotropic angular distribution in Legendre polynomial
representation is given for the 4.438-MeV gamma ray, obtained by
fitting the measurements of Nelson et al. [Ne99].
MT=102 (N,GAMMA) PHOTON ANGULAR DISTRIBUTIONS
All gamma rays from radiative capture are assumed to be
isotropic.
MT=103 (N,PGAMMA) PHOTON ANGULAR DISTRIBUTIONS
Anisotropic angular distributions in Legendre polynomial
representation are given for the 0.2774-, 0.297-, and 0.3975-MeV
gamma rays, obtained by fitting the measurements of Nelson et
al. [Ne99]. The angular distributions for all remaining gamma
rays are assumed to be isotropic.
MT=104 (N,DGAMMA) PHOTON ANGULAR DISTRIBUTIONS
An anisotropic angular distribution in Legendre polynomial
representation is given for the 5.2701-MeV gamma ray, obtained
by fitting the measurements of Nelson et al. [Ne99]. The
angular distributions for all remaining gamma rays are assumed
to be isotropic.
MT=105 (N,TGAMMA) PHOTON ANGULAR DISTRIBUTIONS
All gamma rays from (n,tg) reactions are assumed to be
isotropic.
MT=107 (N,ALPHA GAMMA) PHOTON ANGULAR DISTRIBUTIONS
Anisotropic angular distributions in Legendre polynomial
representation are given for the 0.1693-, 3.6845- and 3.8538-
MeV gamma rays, obtained by fitting the measurements of Nelson
et al. [Ne99]. Isotropic angular distributions are assumed for
all the remaining gamma rays.
****************************************************************
SUMMARY OF DATA VALIDATION OF THIS FILE AGAINST INTEGRAL
BENCHMARKS
KAPL (Weinman, Caro, Lubitz) performed a number of data
validation benchmark calculations to test the performance of this
file (June-August 2001). This O16 evaluation gives consistently
good results for the 21 CSWEG solution critical calculations, the
liquid-oxygen broomstick neutron-transmission experiment, and the
neutron age in water experiment (see below for more details).
A) 21 CSWEG solution critical calculations. Weinman calculated a
set of 21 ORNL and Rocky Flats benchmark solution criticals used
for CSEWG analyses. These calculations were run with ENDF/B-VI
release 5 U235 (Leal,Larson,wright,Derrien) and hydrogen (332.0
mbarns 2200m/s). Four different oxygen 16 cross section
evaluations were considered.
1. KAPL-Caro
2. This evaluation (which contains the KAPL data below 3.4 MeV)
3. ENDF/B-VI MOD 2
4. JENDL 3.2
All four O16 cross section evaluations gave good reactivity
responses versus our fitting parameter above-thermal-leakage ATL.
The ATL parameter is a sensitive trending variable to high energy
scattering cross sections. All four O16 evaluations produced
eigenvalues whose mean values were all close to unity and only
the older ENDF/B-VI.2 cross section evaluation gave a slight
reactivity trend (about .0020 Delta Keff over the range). The
average eigenvalues and slopes are listed below.
Library Av. Keff Slope
KAPL-Caro 0.9993 +.0001
This file 0.9996 +.0004
ENDF/B-VI.2 1.0003 +.0032
JENDL 3.2 1.0004 -.0002
Thus the reactivity trend, labeled "slope" in the table above, is
much smaller in the new file compared to the previous ENDF/B-VI.2
evaluation.
B) The liquid-oxygen broomstick experiment. The oxygen window at
2.3 MeV is the most important feature at which energy the
greatest transmission takes place. The new evaluation produces
close to exact agreement with the experiment in the energy range
of the oxygen window. The previous ENDF/B-VI value is slightly
below the experimental value. At energies higher than 5.5 MeV,
the new evaluation produces slightly better results than does the
previous ENDF/B-VI results.
C) Neutron age in water. KAPL obtained 26.4 to be compared
against an experimental value of 26.6 +/- 0.6. The previous
ENDF/B-VI file gave a result of 26.3.
Additionally, A.C. (Skip) Kahler at Bettis lab undertook
benchmark testing of this file (memo, May 16, 2001) against
thermal benchmarks documented in the Int. Handbook of Evaluated
Criticality Safety Benchmark Experiments, as well as the L5 and
L6 ORNL benchmarks. From a thermal reactor benchmark perspective,
there is little to distinguish the performance of the present
file compared to the previous ENDF file and JENDL-3.2.
*****************************************************************
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