As discussed, the microscopic absorption cross section varies significantly as neutron energy varies. The microscopic cross sections provided on most charts and tables are measured for a standard neutron velocity of 2200 meters/second, which corresponds to an ambient temperature of 68F. Therefore, if our material is at a higher temperature, the absorption cross section will be lower than the value for 68'F, and any cross sections which involve absorption (for example, ) must be corrected for the existing temperature.

The following formula is used to correct microscopic cross sections for temperature. Although the example illustrates absorption cross section, the same formula may be used to correct capture and fission cross sections.

where:

NOTE: When using this formula, all temperatures must be converted to R or K.

Example:

What is the value of _ffor uranium-235 for thermal neutrons at 500F? Uranium-235 has a _fof 583 barns at 68F.

Solution: