Experiment and Analysis of Induced Activities in Concrete Irradiated by 14-MeV Neutrons

Irradiation of concrete aggregates by 14 MeV neutrons was performed to investigate the activation characteristics of concrete, and to verify the calculation code system THIDA using the FNS facility. From the result it was proven that ⁴²K, ²⁴Na, ⁴³K, ⁴⁸Sc, ⁴⁷Ca, ⁴⁶Sc, and ⁵⁴Mn, in half life order, make an important contribution to the total activity. In addition, a comparison between experiment and calculation was made. For ²⁴Na and ⁵⁴Mn, whose cross sections were well estimated, good agreement between experiment and calculation was obtained, which proved the validity of the calculational code. For reaction rates caused by calcium and titanium isotopes, however, calculational results that differed from experimental ones between −20 % to +40 % were obtained. This inconsistency was caused by the uncertainty of the cross section around 14 MeV, because the incident neutron energy was almost 14 MeV. Cross section measurements around 14 MeV of these reactions were performed systematically. Since all samples, except ⁴⁸Ca, were separated isotopes and were irradiated in the same irradiation field, highly precise data with small relative error could be obtained. Consequently, calculations were performed again using measured cross section values, and then agreement between experiment and calculation was improved with ± 10 %.