The reaction cross sections averaged over a 235U fission neutron spectrum have been measured for the 45Sc(n,)42K, 45Sc(n,2n)44Scg, and 45Sc(n,2n)44Scm threshold reactions. The values found for these cross sections are, respectively: 308 ± 16 b, 27.3 ± 1.3 b, and 22.0 ± 2.7 b, using 111 ± 3 mb as the averaged cross section for the 58Ni(n,p)58Com+g reaction that was used as a standard. To the authors' knowledge, these are the first experimental determinations of the 45Sc(n,2n)44Scg and 45Sc(n,2n)44Scm spectrum-averaged cross sections, which were measured using a new method for the case when both the ground and an isomeric state are generated.

By fitting with a suitable function the experimental differential cross sections found in the EXFOR data file for each of these reactions, the corresponding spectrum-averaged cross sections have been calculated for nine different analytical representations of the 235U fission neutron spectrum. This calculation was also performed for the representation based on the Madland-Nix model of prompt fission neutrons. The agreement between calculated and measured values is in general excellent for the 45Sc(n,)42K low-threshold reaction. However, the agreement is rather poor for the 45Sc(n,2n) high-threshold reactions, except for two, Maxwellian-type, representations tried. Since it is well known that Watt-type representations, rather than the Maxwellian type, produce an overall better description of the 235U fission spectrum, the recommended analytical representations to be used are the Watt type. Taking into account their poor performance for high-threshold reactions and recognizing the practical importance of having an analytical representation that agrees with experimental data in the whole energy range, two new representations are presented, based on the one recommended for the ENDF/B-V file, for the 235U fission neutron spectrum, whose main merit is better agreement with experimental results.