Measurement of the neutron capture cross section for 209 Bi(n,γ) 210g Bi in the epithermal energy range

摘要: The epithermal neutron capture cross section of 209 Bi(n,γ) 210g Bi was measured by the activation method at the Xi'an Pulsed Reactor, and the associated uncertainties were discussed in detail. A 1 mm-thick cadmium box was used in the experiment to shield thermal neutrons for obtaining an epithermal neutron field, and the neutron fluence rate was determined using gold and manganese monitors. After irradiation, the bismuth samples were chemically processed, and the activity of 210 Po was measured via spontaneous deposition α-spectrometry. Interferences were eliminated by subtracting the background radioactivity from unirradiated samples. Based on the measured activity, the capture cross section of this reaction in the epithermal neutron energy region was calculated to be (80.23+4.84) mb, and the corresponding average epithermal neutron capture cross section was (6.62+0.40) mb. This result is in good agreement with the JENDL/AD-2017 evaluated nuclear data library. It can provide a reference for further constraining the resonance parameters of the 209 Bi neutron capture reaction and reducing discrepancies among different evaluated libraries. Moreover, the technical route established in this work can be applied to the experimental measurement of the 209 Bi(n,γ )210g Bi capture cross section, which enables accurate evaluation of 210 Po production yield and radiation safety analysis for lead-bismuth fast reactors.