Approximation of Precompound Effects in Hauser-Feshbach Codes for Calculating Double Differential ( n, xn ) Cross Sections

A simplified method for approximating precompound nuclear reaction effects in Hauser-Feshbach codes for the calculation of double differential (n,xn) cross sections is presented. The method is developed from an existing quantum mechanical formula of unified compound and precompound reaction theories. The compound part of the unified formula is made identical to that of Hauser and Feshbach by applying the unified level-density formulas derived previously for the two theories. The precompound part, much more complicated than the compound part, is simplified and globally parameterized for practical purposes. Calculated double differential (n,xn) cross sections at 14 and 26 MeV for iron, niobium, and bismuth are shown to be in good agreement with the available experimental data.

[1]  D. M. Hetrick,et al.  Calculated neutron-induced cross sections for /sup 58,60/Ni from 1 to 20 MeV and comparisons with experiments , 1987 .

[2]  Xiangjun Shi,et al.  Effects of angular-momentum conservation in unified pre-equilibrium and equilibrium reaction models , 1987 .

[3]  D. M. Hetrick,et al.  Calculated neutron-induced cross sections for /sup 53/Cr from 1 to 20 MeV , 1987 .

[4]  D. M. Hetrick,et al.  Update of ENDF/B-V Mod 3 iron: neutron-producing reaction cross sections and energy-angle correlations , 1986 .

[5]  C. Fu.  Simplified Spin Cutoff Factors for Particle-Hole Level Densities in Precompound Nuclear Reaction Theory , 1986 .

[6]  C. Fu.  Implementation of on Advanced Pairing Correction for Particle-Hole State Densities in Precompound Nuclear Reaction Theory , 1984 .

[7]  D. M. Hetrick,et al.  Evaluated neutron-induced cross sections for /sup 40/Ca from 20 to 40 MeV , 1982 .

[8]  P. Hodgson.  Pre-equilibrium processes in nuclear reactions , 1981, Nature.

[9]  Herman Feshbach,et al.  The statistical theory of multi-step compound and direct reactions , 1980 .

[10]  S. Pearlstein.  Analysis of Neutron Emission Spectra from 14-MeV Neutron Reactions , 1978 .

[11]  C. Kalbach.  Exciton number dependence of the Griffin model two-body matrix element , 1978 .

[12]  Leader,et al.  Erratum: Spin-dependent phenomena induced by electromagnetic-hadronic interference at high energies , 1978, Physical review. D, Particles and fields.

[13]  H. Sakai,et al.  Gamma rays and neutrons following preequilibrium 165Ho(p, xcnypγ) reactions at Ep = 60 MeV , 1978 .

[14]  C. Kalbach.  The Griffin model, complex particles and direct nuclear reactions , 1977 .

[15]  R. Weiner,et al.  Diffusion of heat in nuclear matter and preequilibrium phenomena , 1977 .

[16]  F. Perey,et al.  Calculated neutron cross sections for Cu and Nb up to 32 MeV for neutron damage analysis , 1976 .

[17]  C. Fu.  Consistent calculations of (n,x) and (n,xγ) cross sections for 40CA En = 1–20 MeV☆ , 1976 .

[18]  H. Vonach,et al.  Level density parameters for the back-shifted fermi gas model in the mass range 40 < A < 250 , 1973 .

[19]  E. Plechaty,et al.  Measurements and Calculations of the Neutron Spectra from Iron Bombarded with 14-MeV Neutrons , 1973 .

[20]  M. Blann,et al.  The pre-equilibrium statistical model: Description of the nuclear equilibration process and parameterization of the model , 1971 .

[21]  J. Griffin,et al.  Statistical Model of Intermediate Structure , 1966 .

[22]  A. G. W. Cameron,et al.  A COMPOSITE NUCLEAR-LEVEL DENSITY FORMULA WITH SHELL CORRECTIONS , 1965 .

[23]  P. Hodgson,et al.  The calculation of neutron cross-sections from optical potentials , 1964 .

[24]  R. Thomas,et al.  R-Matrix Theory of Nuclear Reactions , 1958 .

[25]  G. R. Satchler.  THE ANGULAR CORRELATION OF THREE NUCLEAR RADIATIONS , 1954 .

[26]  M. E. Rose,et al.  Some Properties of the Racah and Associated Coefficients , 1952 .

[27]  L. Biedenharn,et al.  The Angular Distribution of Scattering and Reaction Cross Sections , 1952 .

[28]  Hans A. Bethe,et al.  An Attempt to Calculate the Number of Energy Levels of a Heavy Nucleus , 1936 .

[29]  Hamada,et al.  Superhyperfine interaction and spin-lattice relaxation of an interstitial iron impurity in silicon. , 1987, Physical review. B, Condensed matter.

[30]  C. Kalbach.  Improved implementation of pairing corrections in exciton model particle-hole state densities , 1987 .

[31]  C. E. Brient,et al.  NEUTRON EMISSION CROSS SECTIONS AT 25. 7 MeV: 51V, 56Fe, 65Cu, 93Nb, AND 209Bi. , 1983 .

[32]  F. D. Becchetti,et al.  NUCLEON--NUCLEUS OPTICAL MODEL PARAMETERS, A > 40, E < 50 MeV. , 1969 .

[33]  H. D. Ferguson,et al.  NUCLEAR LEVEL DENSITIES IN INTERMEDIATE AND HEAVY NUCLEI. , 1967 .

[34]  G. Igo,et al.  Theoretical reaction cross sections for alpha particles with an optical model , 1962 .