Production of Cs-129 tracer by using ion beam bombardment for positron imaging applications

Suzui, Nobuo; Yin, Y.-G.; Kawachi, Naoki; Fujimaki, Shu

We are trying to establish new technologies of radiotracer imaging which can visualize and analyze the movement of radiocesium in the soil-plant system by using a positron-emitting tracer imaging system (PETIS). Our objective in the present project is to establish a production method for Cs-129, a positron-emitting radionuclide, by using ion beam bombardment, and to realize positron imaging of radiocesium in intact plants. Target plates with a thickness of 0.55 mm were made by pressing pure chemical reagents of NaI and KI for ion beam bombardment. These targets were irradiated with helium ion beam for 20 minutes, and 12 hours later, solved in pure water and purified with an anion-exchange column for removal of iodide ions. Finally, the collected solution was subjected to nuclide analysis using a Ge semiconductor detector. As a result, Cs-129 was identified as the main product from the both targets, but some by-products were also detected. The harvested amounts of Cs-129 after purification with the anion-exchange column were 1.2-1.6 MBq. We estimate that approximately 13 MBq of Cs-129 in total is required to obtain serial images of sufficient quality by every 1 hour from the PETIS measurements. Therefore, the present results suggest that the positron imaging with Cs-129 tracer and intact plants is feasible by approximately 3 hours of ion beam bombardment.