Measurement of (γ, n) Reaction Cross Section for Long-lived β-emitting Radionuclide¹²⁹I by using Bremsstrahlung Photons

Abstract

Many long-lived non-gamma emitting radioactive nuclei such as 129 I, 14 C and 93 Zr are produced as wastes from nuclear fuel cycle facilities. They are called "difficult-to-measure" radio nuclei. Among them 129 I is a long-livedemitting isotope with a half-life of 1.57 x 10 7 years. Iodine compounds are mobile in the vadose zone and groundwater and increase a significant long-term risk. Transmutation of 129 I is a challenging issue in nuclear waste management and disposal. If 129 I is transmuted into 128 I (half life; 25 minutes), it can easily be measured by a Ge detector. However, the 129 I( , n) reaction cross section has not been measured so far. In this study we have measured the inclusive 129 I( , n) 128 I cross section by using bremsstrahlung photons. The bremsstrahlung photons were produced from a 30-MeV electron linac. Measured average activation cross section agrees with 12% deviation from the evaluated one in the IAEA photonuclear data library. Gamma and neutron fluxes for the ( , n) and the (n, ) reaction were also calculated by the EGS and the MCNP codes.