Neutron capture cross-section measurement by mass spectrometry for Pb-204 irradiated in JRR-3

Reliable neutron capture cross sections of lead isotopes are necessary for the development of lead or lead-bismuth cooled fast reactors. Although Pb-204 has the smallest natural abundance in stable Pb isotopes, its neutron capture cross-section data are important because a long-lived radionuclide Pb-205 (T-1/2 = 17.3 million years) is produced by a neutron capture reaction on Pb-204. This study applied a mass spectrometry method to measure the neutron capture cross section of Pb-204. An enriched Pb-204 sample was irradiated for 24 days with a neutron flux on the order of 10(13) n/cm(2)/sec at the Japan Research Reactor-3. The irradiated Pb-204 sample was analyzed by thermal ionization mass spectrometry to obtain the isotopic ratio between Pb-205 and Pb-204. Consequently, the thermal-neutron capture cross-section of Pb-204 was found to be 0.536 +/- 0.030 barns.