Measurement of the Photonuclear (,n) Reaction Cross Section for ¹²⁹I Using Bremsstrahlung Photons

Nuclear waste contains a significant amount of long-lived non-gamma-emitting nuclei such as ¹²⁹I and ¹⁴C. A method of nondestructive detection for monitoring long-lived waste products is proposed as an application of the (,n) reaction. This method is useful for surveying long-lived "difficult-to-measure" nuclides, e.g., ¹²⁹I. Iodine-128 produced from the reaction of ¹²⁹I(,n)¹²⁸I emits gamma rays that can easily be measured by a gamma-ray counter. We measured the inclusive photonuclear ¹²⁹I(,n)¹²⁸I reaction cross section induced by bremsstrahlung photons. The photons were produced at a Ta target bombarded by 30-MeV electrons from a linear accelerator. The intensity of the slow neutrons was considered in the reactions of ¹²⁷I(n, )¹²⁸I and ¹²⁹I(n, )¹³⁰I. The activity of ¹²⁸I was measured by a high-purity germanium spectrometer. The gamma-ray flux and the neutron flux were calculated using the EGS and MCNP codes, respectively. The average activation cross section of the ¹²⁹I(,n)¹²⁸I reaction had a 12% deviation from the evaluated International Atomic Energy Agency photonuclear data.