Nuclear data for reactor production of ¹³¹Ba and ¹³³Ba

The newest radioisotope for brachytherapy treatment of prostate cancer is ¹³¹Cs (t_1/2 = 9.69 d, 100% EC). Generated via electron capture decay of ¹³¹Ba (t_1/2 = 11.6 d, 100% EC), ¹³¹Cs has been used in brachytherapy for prostate cancer since 2004. The ¹³¹Ba parent is produced through neutron capture of enriched ¹³⁰Ba in a nuclear reactor. For large-scale production of ¹³¹Ba, an accurate knowledge of production and burnup cross sections of ¹³¹Ba are essential. In this paper, we report two group cross sections (thermal and resonance integrals) for ¹³⁰Ba and ¹³¹Ba and a new measure of the half-life of ¹³¹Ba. Targets consisting of milligram quantities of enriched ¹³⁰Ba (∼35%) were irradiated in Oak Ridge National Laboratory's High Flux Isotope Reactor at thermal and resonance neutron fluxes of (1.9-2.1) × 10¹⁵ and (5.8-7.0) × 10¹³ neutrons·cm^-2 s^-1, respectively, for durations ranging from 3 to 26 days. In addition, cadmium covered samples of ¹³⁰Ba were irradiated for 1 hour at 12.6% full reactor power (10.7 MW). The yield of ¹³¹Ba approaches a saturation value of ∼60 GBq (∼1.6 Ci) per mg of ¹³⁰Ba for 20 days irradiation at a thermal neutron flux of 1.8 × 10¹⁵ n·s^-1·cm^-2, with a thermal/epithermal ratio of ∼30. Under the above experimental conditions, the two group cross sections of ¹³⁰Ba are 6.9 ± 0.5 b (thermal, σ⁰) and 173 ± 7 b (resonance, I⁰). These values represent the sum of cross sections to metastable and ground states of ¹³¹Ba. For ¹³¹Ba, the empirically measured thermal cross section is 200 ± 50 b assuming an I⁰/σ⁰ of 10. This cross section is reported for the first time. Further, the half-life of ¹³¹Ba was remeasured to be 11.657 ± 0.008 d. Lastly, this study also resulted in the co-production of ¹³³Ba (t_1/2 = 10.52 y, 100% EC). The experimental yield of ¹³³Ba is ∼370 MBq (∼10 mCi) per mg of ¹³²Ba (thin target) for one cycle irradiation in the High Flux Isotope Reactor, and measured two-group ¹³²Ba cross sections are 7.2 ± 0.2 b and 39.9 ± 1.3 b. These values also represent the sum of cross sections to metastable and ground states of ¹³³Ba.