New calculation of prompt fission neutron spectra and average prompt neutron multiplicities

Journal Article · Tue Jun 01 04:00:00 EDT 1982 · Nucl. Sci. Eng.; (United States)

DOI:https://doi.org/10.13182/NSE82-5· OSTI ID:7156632

Madland, D G; Nix, J R

On the basis of standard nuclear evaporation theory, the authors calculate the prompt fission neutron spectrum N(E) as a function of both the fissioning nucleus and its excitation energy. To simulate the initial distribution of fission-fragment excitation energy and the subsequent cooling of the fragments as neutrons are emitted, they take the distribution of fission-fragment residual nuclear temperature to be triangular in shape, extending linearly from zero to a maximum value T /SUB m/ . This maximum temperature is determined from the average energy release, the separation energy and kinetic energy of the neutron inducing fission, the total average fission-fragment kinetic energy, and the level density parameter of the Fermi gas model. The neutron energy spectrum for fixed residual nuclear temperature is integrated over this triangular distribution to obtain the neutron energy spectrum in the center-of-mass system of a given fission fragment, which is then transformed to the laboratory system. When the cross section sigma /SUB c/ for the inverse process of compound nucleus formation is assumed constant, N(E) is the sum of a four-term closed expression involving the exponential integral and the incomplete gamma function for the light fragment and an analogous result for the heavy fragment. The authors also calculate N(E) by numerical integration for an energy-dependent cross section sigma /SUB c/ that is obtained from an optical model; this shifts the peak in N(E) to somewhat lower neutron energy and changes the overall shape slightly.

• Research Organization: Los Alamos National Laboratory, Theoretical Division P.O. Box 1663, Los Alamos, New Mexico 87545
• OSTI ID: 7156632
• Journal Information: Nucl. Sci. Eng.; (United States), Journal Name: Nucl. Sci. Eng.; (United States) Vol. 81:2; ISSN NSENA
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
220100* -- Nuclear Reactor Technology-- Theory & Calculation
BARYONS
CALCULATION METHODS
CENTER-OF-MASS SYSTEM
COMPARATIVE EVALUATIONS
CONFIGURATION
CROSS SECTIONS
ELEMENTARY PARTICLES
EMISSION
ENERGY
ENERGY DENSITY
ENERGY LEVELS
ENERGY SPECTRA
ENERGY-LEVEL TRANSITIONS
EXCITATION
FERMIONS
FISSION
FISSION FRAGMENTS
FISSION NEUTRONS
HADRONS
HEAVY NUCLEI
KINETIC ENERGY
LIGHT NUCLEI
MULTIPLICITY
NEUTRON EMISSION
NEUTRON SPECTRA
NEUTRONS
NUCLEAR FRAGMENTS
NUCLEAR REACTIONS
NUCLEAR TEMPERATURE
NUCLEI
NUCLEONS
OPTICAL MODELS
PROMPT NEUTRONS
SPECTRA
TEMPERATURE DISTRIBUTION
TRIANGULAR CONFIGURATION