Westcott factor

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The Westcott factor is a physical number that can be used to establish a relationship between the cross sections σ for neutron capture of a specific nuclide at different temperatures. The cross-section is usually given for a temperature of 20 ° C, which corresponds to a neutron speed of 2200 m / s. The reason for this value is explained by the fact that the radiation tubes are usually thermally decoupled from the reactor and their temperature is therefore around ambient temperature. Since the most varied, mostly higher temperatures prevail in reactors, the cross-section for thermal neutrons is often not sufficient for calculations of the physics of the reactor.

Therefore, CH Westcott developed a method to convert the cross section at room temperature σ₀ into the cross section at the desired temperature. For the calculation, the neutron spectrum is described as a superposition of two different neutron spectra. The first component is formed by the temperature-dependent Maxwellian velocity distribution of the neutrons, while the second component consists of epithermal neutrons , whose frequency distribution shows a decrease with increasing neutron velocity .

If the epithermal component in the neutron spectrum is neglected, the Westcott factor (g) is the quotient of the average cross-section at Maxwell's velocity distribution and the cross-section at a neutron speed of 2200 m / s.

If the cross-section decreases reciprocally with the speed, the Westcott factor is exactly 1.0.

Web links

  • B. Pritychenko, SF Mughabghab: Neutron Thermal Cross Sections, Westcott Factors, Resonance Integrals, Maxwellian Averaged Cross Sections and Astrophysical Reaction Rates Calculated from the ENDF / B-VII.1, JEFF-3.1.2, JENDL-4.0, ROSFOND-2010 , CEND L-3.1 and EAF-2010 Evaluated Data Libraries . In: Nuclear Data Sheets . tape 113 , no. December 12 , 2012, p. 3120-3144 , doi : 10.1016 / j.nds.2012.11.007 , arxiv : 1208.2879 .

Individual evidence

  1. ^ Carl H. Westcott: The specification of neutron flux and nuclear cross-sections in reactor calculations . In: Journal of Nuclear Energy . tape 2 , no. 1-2 , 1955, pp. 59-75 , doi : 10.1016 / 0891-3919 (55) 90017-6 .
  2. ^ A b Nuclear Data for Safeguards. Retrieved January 23, 2017 .