Neutron Capture Cross Sections and Resonances of Iodine-127 and Iodine-129

Neutron capture by ^127,129I has been measured using the Oak Ridge Electron Linear Accelerator as a pulsed neutron source. Neutron energies were determined by time-of-flight. Resonance peaks were parameterized for radioactive ¹²⁹I up to 3400 eV and for stable ¹²⁷I from 2660 to 4260 eV. Average capture cross sections were derived for ¹²⁹I from 3 to 500 keV and for ¹²⁹I from 3 to 2200 keV. Over the 3- to 100-keV range, the ¹²⁹I cross sections average ∼70% of the corresponding ¹²⁷I cross sections but show much more fluctuation as a function of energy. The greater fluctuation is attributed to the approximately three times wider level spacing.