Feasibility study of radioisotope¹³²Cs production using accelerator-based neutrons

We propose that¹³²Cs (E_γ = 668 keV and T_1/2 = 6.5 d) can replace¹³⁷Cs (E_γ = 662 keV and T_1/2 = 30 y) as a new environmental tracer of cesium. The alternative tracer,¹³²Cs, can potentially reveal the short-time dynamics in an environment, which are considered to dominate radioactive cesium absorption after nuclear accidents. We first investigate the production yield and radioactive purity of¹³²Cs in a production experiment at the Cyclotron and Radioisotope Center of Tohoku University. The¹³²Cs was produced via the¹³³Cs(n,2n) reaction with neutrons generated by bombarding accelerated deuterons onto a 4 mm-thick neutron converter made of carbon. The generated neutrons were then irradiated onto a Cs₂CO₃ sample. The experiment yielded 102.2 kBq/g of¹³²Cs, sufficient for tracing environmental cesium. The radioactive purity reached 98%, indicating negligible amounts of by-products. Next, a¹³²Cs tracer experiment was performed on three different soil samples: an andosol soil, a haplic fluvisol soil, and a gleyic fluvisol soil. This feasibility study confirmed that the new tracer can measure soil cesium distributions as adequately as the¹³⁷Cs tracer. Thus, we conclude that¹³²Cs is a promising alternative environmental tracer of 13₇ Cs.