Thermal-neutron capture cross sections and resonance integrals of the ²⁴³Am(n,γ)^244gAm and ²⁴³Am(n,γ)^244m+gAm reactions

ABSTRACT

The thermal-neutron capture cross sections (σ₀) and resonance integrals (I₀) were measured for the ²⁴³Am(n,γ)^244gAm and ²⁴³Am(n,γ)^244m+gAm reactions by a neutron activation method. Americium-243 samples were irradiated with a pneumatic tube and a hydraulic conveyer installed in the research reactor in Institute for Integral Radiation and Nuclear Science, Kyoto University. Alloy wires of Au/Al, Co/Al or Co foils were used as neutron monitors to measure thermal-neutron fluxes and epi-thermal Westcott’s indexes at irradiation positions. A 25-μm-thick gadolinium foil was used to separate reactions due to thermal- and epi-thermal neutron components, and a value of 0.133 eV was taken as a corresponding cut-off energy. Gamma-ray spectroscopy was applied to measure radioactivity of neutron monitors and the ground state of reaction products, while alpha-ray spectroscopy was applied to measure that of target ²⁴³Am and final reaction product ²⁴⁴Cm through the decay of ^{244m, 244g}Am. By utilizing Westcott’s convention, the σ₀ and I₀ values were derived as 4.73 ± 0.27 barn and 96.5 ± 8.9 barn for the ²⁴³Am(n,γ)^244gAm reaction, and 88.5 ± 4.0 barn and 2.30 ± 0.20 kilobarn for the ²⁴³Am(n,γ)^244m+gAm reaction, respectively. The present result of σ₀ for the production of ^244m+gAm agreed with the reported value of 87.7 ± 5.4 barn measured with a time-of-flight method within the limits of uncertainties.

KEYWORDS:

• Americium-243
• americium-244m
• americium-244g
• curium-244
• thermal-neuron capture cross section resonance integral neutron activation method
• Kyoto university reactor

Acknowledgments

This work has been carried out in part under the Visiting Researcher’s Program of the Institute for Integrated Radiation and Nuclear Science, Kyoto University. The authors would like to appreciate the staff of Kyoto University for their support: Prof. Tsutomu OTSUKI, Prof. Jun-ichi HORI, Messrs Daisuke MAKI, Ryo OKUMURA, Yuto IINUMA and Hisao YOSHINAGA. One of the authors (S.N.) would also like to express my gratitude to Dr. Osamu IWAMOTO and Dr. Hideo HARADA of JAEA for their constructive comments and suggestions. Present study includes the result of ‘Research and Development for accuracy improvement of neutron nuclear data on minor actinides’ entrusted to the Japan Atomic Energy Agency by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT).

Disclosure statement

No potential conflict of interest was reported by the authors.