Imaging of radiocesium uptake dynamics in a plant body by using a newly developed high-resolution gamma camera

We developed a new gamma camera specifically for plant nutritional research and successfully performed live imaging of the uptake and partitioning of ¹³⁷Cs in intact plants. The gamma camera was specially designed for high-energy gamma photons from ¹³⁷Cs (662 keV). To obtain reliable images, a pinhole collimator made of tungsten heavy alloy was used to reduce penetration and scattering of gamma photons. A single-crystal scintillator, Ce-doped Gd₃Al₂Ga₃O₁₂, with high sensitivity, no natural radioactivity, and no hygroscopicity was used. The array block of the scintillator was coupled to a high-quantum efficiency position sensitive photomultiplier tube to obtain accurate images. The completed gamma camera had a sensitivity of 0.83 count s^-1 MBq^-1 for ¹³⁷Cs with an energy window from 600 keV to 730 keV, and a spatial resolution of 23.5 mm. We used this gamma camera to study soybean plants that were hydroponically grown and fed with 2.0 MBq of ¹³⁷Cs for 6 days to visualize and investigate the transport dynamics in aerial plant parts. ¹³⁷Cs gradually appeared in the shoot several hours after feeding, and then accumulated preferentially and intensively in growing pods and seeds; very little accumulation was observed in mature leaves. Our results also suggested that this gamma-camera method may serve as a practical analyzing tool for breeding crops and improving cultivation techniques resulting in low accumulation of radiocesium into the consumable parts of plants.