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

ABSTRACT

Reliable neutron capture cross sections of lead isotopes are necessary for the development of lead or lead-bismuth cooled fast reactors. Although ²⁰⁴Pb has the smallest natural abundance in stable Pb isotopes, its neutron capture cross-section data are important because a long-lived radionuclide ²⁰⁵Pb (T_1/2 = 17.3 million years) is produced by a neutron capture reaction on ²⁰⁴Pb. This study applied a mass spectrometry method to measure the neutron capture cross section of ²⁰⁴Pb. An enriched ²⁰⁴Pb sample was irradiated for 24 days with a neutron flux on the order of 10¹³ n/cm²/sec at the Japan Research Reactor-3. The irradiated ²⁰⁴Pb sample was analyzed by thermal ionization mass spectrometry to obtain the isotopic ratio between ²⁰⁵Pb and ²⁰⁴Pb. Consequently, the thermal-neutron capture cross-section of ²⁰⁴Pb was found to be 0.536 ± 0.030 barns.

KEYWORDS:

• Lead-204
• lead-205
• mass spectrometry
• activation method
• JRR-3

Acknowledgments

The authors would like to greatly appreciate the staff working in the JRR-3 for their cooperation and acknowledge Mrs. Atsushi Yamaguchi, Toshiyuki Takahashi, Masayuki Fujita, and Yuji Sekiya of the facility management section, and Katsuhiko Ishizaki of the JRR3 management section. One of the authors (S.N.) would also like to express gratitude to Dr Osamu Iwamoto of JAEA for their constructive comments and for carefully proofreading the manuscript.