Table of Nuclides Frequently Asked Questions 2.2: Integral Cross Section Definition of 2200 m/s cross section and resonance integrals I have a question regarding the resonance integral. As you know I do web service based on your summary of jendl file. Which contains average cross sections such as thermal value, resonance integral, etc. I found a strange value for Ni-58(n,p). The resonance integral was 8.58666e-1. ( The peak value of actual (n,p) cross section is less than 0.5 barn ! ) My question is:  What is definition of resonance integral ?  What is correct value of resonance integral for Ni-58(n,p) 2200-m/s cross section: calculated from resonance parameters at 0.0253 eV if the resonance parameters are given, or interpolated at 0.0253 eV if no resonance parameters. Resonance integral: integral of sig(E)/E from 0.5 eV to 20 MeV, where E is the neutron energy and sig(E) the cross section. the energy of 0.5 eV is called "cut-off energy". In the case of Ni-58(n,p), the cross section is given in the energy range >from 1.0E-5 eV to 20 MeV, since it Q value is positive. 2200-m/s cross section was obtained by the interpolation. The resonance integral was calculated with the above-mentioned integral.  The result is 0.8587 b. The Ni-58(n,p) cross section given in JENDL-3.2 was obtained by calculation. Therefore very small values are given in the low energy region. Usually, in such cases, we put an effective threshold energy around 100 keV, and replace the cross section with 0.0 below the effective threshold energy. In the case of Ni-58(n,p), we did not do this modification by mistake !                                     - Tsuneo Nakagawa -

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