Thermal-Neutron Capture Cross Sections and Resonance Integrals of the ⁸⁰Se(n,γ)^81m,81gSe Reactions

Abstract

The thermal-neutron capture cross sections (σ_0,m and σ_0,g) and resonance integrals (I _0,m and I _0,g) leading to the isomeric and ground states of ⁸¹Se were measured by the activation method. Samples of high-purity (99.99%) selenium oxide were irradiated in a rotary specimen rack of the research reactor of Rikkyo University. Wires of Co/Al and Au/Al alloys, which have different sensitivities to neutrons in the thermal and epithermal energy regions, were irradiated to monitor the thermal neutron fluxes and the epithermal components at the same position of the rotary specimen rack. The cadmium-shielded samples were also irradiated to obtain the cadmium ratio and the resonance integrals (I _0,m and I _0,g). A high-purity Ge detector was used to measure the γ-rays emitted from the irradiated samples and wires, and reaction rates were calculated from γ-ray yields. On the basis of Westcott's convention, the cross sections were obtained as follows: σ_0,m = 0.057 ± 0.003 b and I _0,m = 0.186 ± 0.014 b leading to ^81mSe, and σ_0,g = 0.536 ± 0.046 b and I _0,g = 0.867 ± 0.102 b leading to ^81gSe.

KEYWORDS:

• selenium-80
• selenium-81
• isomer
• thermal-neutron capture cross section
• resonance
• integral
• activation method
• gamma ray spectroscopy
• measurement