Measurement of (γ, n) reaction cross section for long-lived β-emitting radionuclide¹²⁹I by using bremsstrahlung photons

Many long-lived non-gamma emitting radioactive nuclei such as ¹²⁹I, ¹⁴C and ⁹³Zr are produced as wastes from nuclear fuel cycle facilities. They are called "difficult-to-measure" radio nuclei. Among them ¹²⁹I is a long-lived β-emitting isotope with a half-life of 1.57 × 10⁷ years. Iodine compounds are mobile in the vadose zone and groundwater and increase a significant long-term risk. Transmutation of ¹²⁹I is a challenging issue in nuclear waste management and disposal. If ¹²⁹I is transmuted into ¹²⁸I (half life; 25 minutes), it can easily be measured by a Ge detector. However, the ¹²⁹I(γ, n) reaction cross section has not been measured so far. In this study we have measured the inclusive ¹²⁹I(γ, n)¹²⁸I 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 (γ, n) and the (n, γ) reaction were also calculated by the EGS and the MCNP codes.