Simulation evaluation on a compact monitor for gamma-emitting tracers in plant stems

Non-destructive monitoring of radioactivities derived from radioactive tracers at multiple points in plant stems can be used to evaluate the velocity of element transport in living plants. In this study, we calculated absorption-efficiency distributions for several detector geometries to determine appropriate shapes for non-destructive monitoring of radioactivities in the stem. The efficiency distributions were calculated by Monte Carlo simulations, and the flatnesses and spatial resolutions were evaluated. It was found that the placement of four detectors around the stem could limit the percentage of standard deviation to the mean of the pixel values to less than 5%. We could determine a compact detector geometry with a spatial resolution of 1.35 cm using four small detectors. The detection efficiencies were 0.014, 0.0030 and 0.000 63 cm at the initial gamma-ray energies of 0.5, 1 and 2 MeV, which is sufficiently applicable to detect 10 kBq cm−1 of radioactivity.