))))DOE-HDBK-1019/1-93NUCLEAR CROSS SECTIONS AND NEUTRON FLUXReactor Theory (Neutron Characteristics)NP-02Page 14Rev. 0EffectsofTemperatureonCrossSectionAs discussed, the microscopic absorption cross section varies significantly as neutron energyvaries. The microscopic cross sections provided on most charts and tables are measured for astandard neutron velocity of 2200 meters/second, which corresponds to an ambient temperatureof 68F. Therefore, if our material is at a higher temperature, the absorption cross section willbe lower than the value for 68F, and any cross sections which involve absorption (for example,), ) , ) ) must be corrected for the existing temperature.a c fThe following formula is used to correct microscopic cross sections for temperature. Althoughthe example illustrates absorption cross section, the same formula may be used to correct captureand fission cross sections.where:)= microscopic cross section corrected for temperature)= microscopic cross section at reference temperature (68F or 20C) oT= reference temperature (68F) in degrees Rankine (R) or Kelvin (K)oT= temperature for which corrected value is being calculatedNOTE: When using this formula, all temperatures must be converted to R or K.R= F + 460K= C + 273Example:What is the value of ) for uranium-235 for thermal neutrons at 500F? Uranium-235fhas a ) of 583 barns at 68F. fSolution:
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