Ionic nutrition is essential for plant development. Many techniques have been developed to image and (or) measure ionic movement in plants. Nevertheless, most of them are destructive and limit the analysis. Here, we present the development of radioisotope imaging techniques that overcome such restrictions and allow for real-time imaging of ionic movement. The first system, called macroimaging, was developed to visualize and measure ion uptake and translocation between organs at a whole-plant scale. Such a device is fully compatible with illumination of the sample. We also modified fluorescent microscopes to set up various solutions for ion uptake analysis at the microscopic level. Both systems allow numerical analysis of images and possess a wide dynamic range of detection because they are based on radioactivity.

Conventional positron annihilation lifetime measurements have focused on determining the lifetime and relative intensity of each lifetime component deduced by multi-component analysis or the “mean” lifetime deduced by single-component analysis. So far, little attention has been paid towards the starting time (T 0) on the spectrum’s time axis. When analysing lifetime spectra with multiple components using an exponential function with a single-component, there is a difference between the experimental data and the fitted spectrum. Compensating for this difference causes a shift in the T 0 value in the fitted spectrum. This study examines the shifts in T 0 (ΔT 0) in positron lifetime spectrum analyses of metal samples with defects. We conducted simulations of trapping models and experiments with shot-peened stainless steel, verifying that ΔT 0 changed depending on the defect concentration even when almost all positrons were trapped (full trap). Therefore, we propose ΔT 0 as a new parameter for evaluating positron annihilation lifetime measurements.

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A new positron annihilation lifetime spectrometer consisting of a start γ-ray detector, a stop γ-ray detector, a digital oscilloscope, and a positron detector, which is a plastic scintillator coupled to a photomultiplier tube, is described. A 22Na source is placed between the positron detector and a sample to be studied. γ-ray signals related to positrons annihilating in the positron detector are rejected by anti-coincidence processing. Comparison of the positron lifetime spectrum of a steel strip collected with the new system with that collected with a conventional system using two specimens sandwiching the 22Na source shows that accurate positron lifetime measurements are possible with the new system. The new system does not require cutting of the samples and is potentially applicable to truly nondestructive onsite inspection of various materials such as those used in nuclear power plants, aircraft and cars, etc., by positron annihilation lifetime spectroscopy (PALS).