14-Si- 30 LANL,ORNL EVAL-JUN97 M.B.CHADWICK,P.G.YOUNG,D.HETRICK Ch97,Ch99,He97 DIST-AUG99 REV1- 19990907 ----ENDF/B-VI MATERIAL 1431 REVISION 1 -----INCIDENT NEUTRON DATA ------ENDF-6 FORMAT ****************************************************************** Oct 22,2004, Holly Trellue remade mf6mt5 using corrected gnash code, to fix an earlier bug. Impact is reduced sec. particle prod. for new ENDF/B-VII release ENDF/B-VI MOD 2 Evaluation, June 1996, M.B. Chadwick and P.G. Young, LANL Los Alamos LA150 Library, produced with FKK/GNASH/GSCAN code in cooperation with ECN Petten. 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 below and above 20 MeV. INCIDENT NEUTRON ENERGIES < 20 MeV Below 20 MeV the evaluation is based completely on the ENDF/B- VI.5 (Release 5) evaluation by D. Hetrick, N. Larson, D. Larson, L. Leal, and S. Epperson. INCIDENT NEUTRON ENERGIES > 20 MeV The ENDF/B-VI Release 5 evaluation extends to 20 MeV and includes cross sections and energy-angle data for all significant reactions. The present evauation utilizes a more compact composite reaction spectrum representation above 20 MeV in order to reduce the length of the file. No essential data for applications is lost with this representation. The evaluation above 20 MeV utilizes MF=6, MT=5 to represent all reaction data. Production cross sections and emission spectra are given for neutrons, protons, deuterons, tritons, 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 = 20 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 MF=4 MT= 2 Elastic Angular Distributions MF=6 MT= 5 Production Cross Sections and Energy-Angle Distributions for Emission Neutrons, Protons, Deuterons, Tritons, 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 + Si28 and p + Si28 reactions [Ch97]. We use the GNASH code system [Yo92], which utilizes Hauser-Feshbach statistical, preequilibrium and direct-reaction theories. 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. 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 [Ch96]. The recoil energy distributions are represented in the laboratory system in MT=5, MF=6, and are given as isotropic in the lab system. All other data in MT=5,MF=6 are given in the center-of-mass system. This method of representation utilizes the LCT=3 option approved at the November, 1996, CSEWG meeting. Preequilibrium corrections were performed in the course of the GNASH calculations using the exciton model of Kalbach [Ka77, Ka85], validated by comparison with calculations using Feshbach, Kerman, Koonin (FKK) theory [Ch93]. 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]. DETAILS OF THE n + SI-30 ANALYSIS The neutron total cross section above 20 MeV was obtained by evaluating the nat-Si experimental data, with a particular emphasis on the high-accuracy Los Alamos measurements by Finlay [Fi93]. The Si-28 total cross section, based on nat-Si data, was scaled by 1.047 (an A**2/3 factor) for Si-30. The Madland global medium-energy optical potential [Ma88] was used for neutrons above 46 MeV, and the Wilmore-Hodgson potential was used for lower neutron energies. The Madland global medium-energy optical potential was used for protons above 28 MeV, and the Beccheti-Greenlees potential was used for lower proton energies. In both cases the transition region to the Madland potential was chosen to approximately give continuity in the reaction cross section. For deuterons, the Perey global potential was used; for alpha particles the Moyen potential was used; and for tritons the Beccheti-Greenlees potential was used. While the above optical potentials did describe the experimental proton nonelastic cross section data fairly well, we modified the theoretical predictions slightly to better agree with the measurements, and renormalized the transmission coefficients accordingly. In addition to using Si nonelastic proton cross section measurements, we also were guided by p+Al nonelastic data, scaled by A**2/3. The Si-30 nonelastic cross section was taken by scaling the evaluated Si-28 value by 1.047 (an A**2/3 factor). Inelastic scattering to the 2+ (2.24 MeV) and 4+ (5.95 MeV) states in 30-Si was determined using a coupled-channel ECIS calculation. To produce continuity in the calculated inelastic cross sections up to 150 MeV, we performed an oblate rotational band (0+, 2+, 4+) coupled channel calculation using the Madland medium energy potential (with its imaginary potential reduced by 20%, to approximately account for the coupling). Deformation parameters were chosen to reproduce the JENDL-3 evaluation at 20 MeV (H.Kitazawa et al.). The resulting deformation parameters (beta_2=-0.33, beta_4=0.20) were close to those used for Si-28. The same preequilibrium input parameters were used as for Si- 28, which was benchmarked against (n,xz) data from the Louvain group at 63 MeV, and against unpublished (n,xp) data by Haight et al. for neutrons up to 50 MeV. See our ENDF file-1 for n+28Si for more details. **************************************************************** ENDF/B-VI MOD 1 Evaluation, May, 1996 D.M. Hetrick, D.C. Larson, N.M. Larson, L.C. Leal, S.J.Epperson (ORNL) Complete documentation for this evaluation is found in Hetrick, et al. [He97]. This work employed nuclear model codes including the Distorted Wave Born Approximation (DWBA) program DWUCK [Ku72] and the Hauser-Feshbach code TNG [Fu88],[Fu80],[Sh86]. The TNG code provides energy and angular distributions of particles emitted in the compound and pre-compound reactions, ensures consistency among all reactions, and maintains energy balance. Evaluation work was completed in 1989, except for MT=3, MF=1,2,3,102 which were completed May 1996. The latter results Incorporated a new resonance region analysis. Uncertainty files are provided for all FILE 3 cross sections using methodology described in Hetrick et al. [He91]. DESCRIPTION OF FILES MF=2 RESONANCE PARAMETERS MT=151 Resonance parameters from a new analysis for all three isotopes of silicon, by Leal et al. [Le96], using the multilevel R-matrix analysis code SAMMY [La96]. Energy range 1.0E-5 eV to 1.50 MeV. The following data were included in the analysis: (1) Total cross section data of Perey et al. [Pe72] for natural silicon, measured on the 47-m flight path at the Oak Ridge Electron Linear Accelerator (ORELA) (2) Transmission data of Harvey et al. [Ha96a] for natural silicon measured on the 200-m flight path at ORELA (3) Total cross section data of Larson et al. [La76], measured on the 80- and 200-m flight paths at ORELA (4) 29Si-oxide [Ha96b) and 30Si-oxide [Ha83] transmission data of Harvey et al., measured on the 80-m ORELA flight path (5) Elastic scattering thermal cross section for 30Si 2.490+-0.169 barns from Mughabghab [Mu81]. Capture thermal cross section 0.107+-0.003 barns from Raman et al. [Ra92]. Values given by resonance parameters are 2.500 and 0.107 barns respectively. MF=3 CROSS SECTIONS MT=1 Total cross section 1.E-5 eV to 1.50 MeV taken from resonance parameters evaluation. From 1.50 to 20 MeV, based on 200-m data [Ha96a] for natural silicon. Thermal value = 2.597 barns from (exp.) and 2.590 from resonance parameters. MT=2 Elastic scattering cross sections were obtained by subtracting the nonelastic from the total. MT=3 Nonelastic cross section: sum of MT=4,16,22,28,102,103, 104, and 107. MT=4 Total inelastic cross section: sum of MT=51-56 and 91. MT=16 (n,2n) cross sections calculated by the TNG code [Fu88],[Fu80],[Sh86]. MT=22 (n,na) cross sections calculated by the TNG code. No data available other than alpha emission. MT=28 (n,np) cross sections calculated by the TNG code. No data available other than proton emission. MT=51-56 Inelastic scattering excited levels; results are taken from the code TNG [Fu88],[Fu80],[Sh86] which includes direct interaction cross sections from DWUCK [Ku72] calculations (when data available). MT=91 Inelastic scattering exciting the continuum calculated by code TNG with guidance from (n,xn) emission data. MT=102 (n,g) capture cross section, 1.e-5 eV to 1.50 MeV taken from resonance parameters. From 1.5o to 20 MeV, evaluation based on TNG calculation, normalized to available data at 14.7 MeV. Thermal value = 0.107 barns [Ra92]. MT=103 (n,p) cross sections were calculated by the code TNG [Fu88],[Fu80],[Sh86] from 9.0 to 20.0 MeV. From threshold to 9.0 MeV, taken from ENDF/B-V evaluation. MT=107 (n,a) cross sections were calculated by the code TNG [Fu88],[Fu80],[Sh86]. MT=600-605 (n,p) reaction to discrete levels calculated by code TNG [Fu88],[Fu80],[Sh86]. MT=649 (n,p) continuum protons calculated by code TNG [Fu88], [Fu80],[Sh86]. MT=800-811 (n,a) reaction to discrete levels calculted by the code TNG [Fu88],[Fu80],[Sh86]. MT=849 (n,a) continuum alphas calculated by the code TNG [Fu88],[Fu80],[Sh86]. MF=4 ANGULAR DISTRIBUTIONS MT=2 Angular distributions of secondary neutrons from elastic scattering are taken from the ENDF/B-V evaluation. MF=6 PRODUCT ENERGY-ANGLE DISTRIBUTIONS MT=16 (n,2n) reaction includes simple constant yields for the neutron and 20Si residual, and energy dependent gamma- ray yield based on TNG calculated gamma-ray spectra. TNG calculated normalized distributions are given for each product. (Angular distributions are given only for the outgoing neutron). MT=22 (n,na) reaction includes simple constant yields for the neutron, alpha, and 26Mg residual, and energy- dependent gamma-ray yield based on TNG calculated gamma- ray spectra. Calculated normalized distributions are given for each product. (Angular distributions are given only for the outgoing neutron; isotropy is assumed for the alpha and residual). MT=28 (n,np) reaction includes simple constant yields for the neutron and 29Al residual, and energy dependent gamma- ray yield based on TNG calculated gamma-ray spectra; calculated normalized distributions are given for each product. (Angular distributions are given only for the for the outgoing neutron). MT=51-56 Inelastic scattering exciting levels; each section includes simple constant yields for the neutron and 30Si residual; angular distributions are given for the outgoing neutron (Legendre coefficients computed by DWUCK [Ku72] and TNG [Fu88],[Fu80],[Sh86]). MT=91 Inelastic scattering exciting the continuum includes simple constant yields for the neutron and 30Si residual and energy dependent gamma-ray yield based on TNG calculated gamma-ray spectra; TNG calculated normalized distributions are given for each. (Angular distributions are given only for the outgoing neutron). MT=600-605 (n,p) proton angular distributions to discrete states taken from the TNG calculation. MT=649 (n,p) continuum includes simple constant yields for protons and 30Al residual, and energy-dependent gamma-ray yield based on TNG calculated gamma-ray spectra; calculated normalized distributions are given for each product. MT=800-811 (n,a) alpha angular distributions to discrete states taken from the TNG calculation. MT=849 (n,a) continuum: includes simple constant yields for alphas and 27Mg residual, and energy-dependent gamma-ray yield based on calculated gamma-ray spectra -- calculated normalized distributions are given for each product. MF=12 PHOTON PRODUCTION MULTIPLICITIES MT=51-67 Branching ratios for the levels are given. These ratios were used in the TNG calculation (i.e., the continuum and discrete gammas are separated). MT=102 (n,g) capture spectra based on thermal measurements of Raman et al. [Ra92]. Yields are given for all observed gamma rays. The thermal results are used from 1.e-5 eV to 20 MeV. Some small renormalizations were used on large yields to ensure energy balance. MT=601-605 Branching ratios for the levels are given. These ratios were used in the TNG calculation (i.e., the continuum and discrete gammas are separated). MT=801-811 Branching ratios for the levels are given. These ratios were used in the TNG calculation (i.e., the continuum and discrete gammas are separated). MF=14 PHOTON ANGULAR DISTRIBUTIONS MT=51-67,102,601-605,801-811 All gamma ray angular distributions assumed to be isotropic. MF=33 COVARIANCES OF NEUTRON CROSS SECTIONS Uncertainty files are given for all FILE 3 reactions, using the methodology described in Hetrick et al. [He91], and used for ORNL ENDF/B-VI evaluations for isotopes of Cr, Fe, Ni, Cu, and Pb. LB=0,1,8 sub-subsections are utilized. ***************************************************************** REFERENCES [Be69] F.D. 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