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Positron annihilation lifetime measurement has been a destructive analysis method in the sense that it requires cutting the specimen in two pieces, but the anti-coincidence method we developed enables the measurement of positron annihilation lifetime without cutting. In this study, by applying this anti-coincidence method, we developed a small and light portable positron annihilation lifetime measurement equipment for on-site measurements. In order to make the equipment small and light, we used a small photomultiplier tube for the γ-ray detectors, and we determined the detector configuration by simulation and experiment. To evaluate the performance of the developed equipment, we conducted positron annihilation lifetime measurements on shot-peened stainless steel and compared the results to those by the desktop anti-coincidence equipment. Just like the desktop equipment, the developed equipment revealed the increase in the defect density by shot-peening as the change in the positron lifetime, verifying the effectiveness of this equipment.

The macroscopic elastic modulus of a solid-state matter is generally affected by the packing density and average bond strength of the constituent atoms. However, because of the diversity of network connections in oxide glasses, an understanding based on the network structure is also required for precise structural categorisation. Here, we examine the relationship between the elastic modulus and structural parameters, viz., the correlation length of the Boson peak and cavity size calculated from the positron annihilation measurement, of BaO-TiO2-GeO2-SiO2 glasses. The Poisson's ratio correlates with the ratio of the longitudinal and transversal sound velocities, and thermal stability parameter ΔT. The Boson peak frequencies of these glasses at the GeO2-rich region exhibit an apparent plateau behavior, indicating that the rate of change in the sound velocity is similar to that in the correlation length. Although the numerical calculation of the cavity in this glass by positron annihilation spectroscopy is unavailable because of the d -electron of Ti cations, the τ1 value shows a similar compositional dependence as the correlation length of the Boson peak. It is expected that a combination of elastic modulus and inelastic light scattering of glasses will be helpful in understanding glass-forming melts.

Positron annihilation lifetime measurements were performed on polyethylene films [low-density polyethylene and ultra-high molecular weight polyethylene (UHMWPE)] with a thickness of 15–2000 μm using a Na-22 positron source enclosed in a Kapton film. For thin films, some positrons will pass through the film and annihilate behind it. Using a single film in a commercial anti-coincidence system, by placing an annealed stainless steel (SUS304) cover behind the sample, it is possible to sufficiently measure the long-lifetime ortho-positronium (o-Ps) component even in thin films. Additionally, calculated intensities of the o-Ps component determined from the estimated film transmittance agreed well with the measured values. Furthermore, by applying this method to uniaxially stretched UHMWPE, we were able to observe structural changes owing to the stretching consistent with shorter measured o-Ps lifetime and increased o-Ps intensity.

We examined the feasibility of on-site non-destructive defect analysis using positron annihilation lifetime measurement. This analysis requires a short measurement time and lattice defect information has to be extracted from positron lifetime data that involve high statistical uncertainties. In this study, we simulated positron lifetime spectra for a short measurement of approximately 1 min, using experimental positron lifetimes of shot-peened stainless steel, and studied the variations of the center-of-gravity positron lifetime, the “mean” positron lifetime and the shift in the starting time (ΔT 0) with the positron trapping rate into defects, which is a physical quantity proportional to the lattice defect density. As a result, distinguishing the positron lifetime spectra of different trapping rates in a range of up to 1 × 1011 s−1 was possible by creating a 2D plot of the “mean” positron lifetime and ΔT 0.

When analyzing positron annihilation 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 starting time (T 0) in the fitted spectrum. Previously, we applied single-component analysis to the positron lifetime spectrum of a defect-containing metal and confirmed the effectiveness of the shift in T 0 (ΔT 0) for defect analysis. To optimally use the T 0 variation for defect analysis, however, it is necessary to minimize the drift in the positron lifetime spectrum due to the temporal instability of the photomultiplier tube and high-voltage power supply. In this study, we report significant suppression of the drift by using dual start/stop data acquisition (dual acquisition), which employs each of the two γ-ray detectors to acquire start and stop signals.

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.

Sealed radioactive sources of 22Na for positron annihilation lifetime spectroscopy (PALS), free from the legal regulations, are commercially available from an American company. However, thick foils are used to seal 22Na in these sources and large fractions of the positrons annihilate in the sealing materials. Further, it is pointed out that a long lifetime component over 1 ns appears in the positron lifetime spectrum acquired with the Kapton sealed source (POSK-22, IPL Inc.). In this research, attempts were made to develop high quality sealed positron sources, potentially free from regulations, for ubiquitous application of PALS. The sources prepared in the present work are of high quality and applicable to our new PALS, which does not require sample cutting and is potentially applicable to truly nondestructive, onsite inspection of various materials

Positron annihilation lifetime spectroscopy (PALS) has widely been used for probing open volume defects in various materials. PALS is in principle non-destructive, yet conventional PALS is not strictly non-destructive because cutting out of two specimens from the material is required. Recently we developed a novel method of PALS, which is potentially applicable to non-destructive, onsite material inspection. In order to explore the possibility of onsite monitoring of polymer degradation by this novel method of PALS, we studied variations of positron lifetime and mechanical properties of ultra high molecular weight polyethylene (UHMWPE) subjected to γ-irradiation. Correlations were found between the mechanical properties and ortho-positronium lifetimes, suggesting the feasibility of non-destructive, onsite monitoring of polymer degradation by PALS. The effect of γ-irradiation on positronium formation is discussed.

A new real-time radioisotope imaging system (RRIS) to study the kinetics of nutrient uptake and transfer of photosynthetic products in a living plant was developed and evaluated through a test run. 14C is a common radioisotope of carbon and useful to trace the photosynthetic products as well as a low energy beta emitter. The rationale of this study was to develop a RRIS that has the ability to detect low energy beta emitters, such as 14C, 35S, and 45Ca. To achieve compatibility between the detection of low energy beta emitters and irradiation of the test plant, an intermittent lighting system was added to the RRIS. Furthermore, a commercially available digital camera was added to the RRIS for acquisition of photographic images of the test plants. The capabilities of the new RRIS were evaluated through a test run by using seedlings of rice plants and 35S-labeled sulfate. It was shown that the new RRIS was able to detect 35S absorbed by rice plant seedlings, and it was able to acquire photon-counting images and photographic images of the test plants simultaneously. Despite some limitations, the new RRIS provides a means to study the kinetics of elements in plants by utilizing low energy beta emitters.

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.

It is very important to visualize the process of nutrient absorption and distribution to study the physiological activity of the plant. We developed a real-time radioisotope (RI) imaging system, where RI tracers were applied to the plant sample. This system allowed the quantitative measurement concerning the uptake of nutrients labeled with radioisotopes, such as 45Ca, 35S, 32P and 14C as long as several days. The β-rays emitted from the sample were converted to light by a CsI(Tl) scintillator and were guided to a highly sensitive CCD camera. The scintillator surface was covered with an Al plate to avoid LED light penetration but allow selected β-ray penetration. We employed Lotus japonicus for the plant sample and observed the 32P-phosphate absorption in roots and the accumulation to the aboveground part of the plant. The environment condition of daytime and night was simulated by the ON/OFF of LED timer and the accumulation manner of the 32P-phosphate in roots and leaves during daytime and night was analyzed. The accumulation of 32P-phosphate in leaves was highly dependant on light irradiation and higher when the LEDs was turned on, whereas the absorption of 32P-phosphate in root was higher when the LEDs was turned off. The transfer function concerning the transportation of phosphate within the plant during the developmental stage was obtained from the analysis of 32P uptake images. We are now trying to get specific moving images of each radioisotope when two kinds of isotopes, such as 32P and 35S, were applied at the same time to the plant, through an image analysis.

We present real-time images of 35S-sulfate uptake in a rapeseed plant visualized by the system we developed. In the leaves of rapeseed plants, 35S accumulated in higher amounts and more rapidly in the more developed leaves. This real-time imaging system can be used to visualize the movement of both 35S and 32P in the same plant. In the pods of rapeseed, images of 35S show that 35S accumulated mostly in the terminal parts; on the other hand 32P, when applied as 32P-phosphoric acid, accumulated in the middle part of the pods.

We present double-tracer autoradiography with 35S and 32P using imaging plates and an aluminum plate to visualize the individual distribution of sulfur and phosphorus in Brassica napus L.. Because of the different attenuation efficiencies of β-rays emitted from 35S and 32P, the specific image of 32P was taken when an aluminum plate was placed between the sample and the imaging plate. The specific image of 35S was obtained by subtracting the 32P image from the 35S and 32P image. It was observed that high amount of 35S was distributed at the edge of the leaves and in root tips. The 32P was distributed throughout the whole plant and it was found that the phosphorous amount was higher at the shoot apical meristems than those in leaves.

In this study, real-time imaging using γ-emitting nuclide, 109Cd, was studied and sensitivity and resolution of the system we developed was evaluated. When RI was applied to the plant, the radiation from the RI distributed throughout the plant was converted to visible light by a scintillator. Then, this weak light was multiplied by a micro-channel plate(MCP)and photographed by a charge-coupled device(CCD)camera. 109Cd emits 88keV γ-rays together with 22keV X-rays, and therefore it is necessary to investigate effective condition for designing an observation system for the measurement of radiation from 109Cd. Analysis was performed to determine which rays, γ-rays or X-rays, were mainly detected by this system and the optimal scintillator thickness for imaging 109Cd was investigated. Then the sensitivity and resolution of the system was evaluated.

We present the real-time RI imaging and analyzing system to study the kinetics of nutrient uptake manner in a living plant. The system allowed light condition for the up-ground part of the plant and continuous dark condition for the root part, therefore, light/dark cycles was set as 16/8 h. There was 9,000 lx of LED lights in an aluminum container where the plant was set. The container was shielded well so that there was no light leakage to damage highly sensitive CCD camera which detected beta-rays from the sample. With this system, RI imaging was able to perform for 6 days without damaging the activity of the plant.

γ-Ray measurement techniques are used in positron emission tomography and positron annihilation lifetime measurement, and require a high time resolution. In this study, we investigated the design conditions for scintillation detectors to improve the time resolution of time-of-flight measurement using a Monte Carlo simulation. The time resolution is strongly affected by the scintillator shape and reflector properties. The result shows that, for thin scintillators, specular reflectors are effective for obtaining a good time resolution, while for thick scintillators, diffuse reflectors are effective. It also shows that, for thin scintillators, the time resolution can be improved by combining specular and diffuse reflectors on the side and bottom surfaces, respectively.

The measurement method and system architecture of a new time-of-flight positron emission tomography (TOF-PET) system are proposed. This system collects scintillation light using optical fibers connected directly to scintillators and measures the position of positron annihilation. Many scintillators are placed cylindrically whereby a pair of scintillators detects a pair of γ-rays generated at the positron annihilation point. Optical fiber circuits, most of which are bundles of optical fibers bound clockwise or counterclockwise around the cylinder of scintillators, collect light signals generated by γ-rays. These light signals are amplified by several photomultiplier tubes and processed using a single digital oscilloscope to determine the TOF of the positron annihilation γ-rays. One of the most important factors in the performance of the TOF-PET system is the TOF resolution. When fiber circuits are used for transmitting light signals, the dispersion of light signals and the decrease in light intensity are the major factors in the deterioration of the TOF resolution. The result of the preliminary experiment leads to the conclusion that the use of optical fibers degrades the intensity of light but does not severely degrade the TOF resolution.

The commonly used γ-ray measurement method employs a technique of transmitting scintillation light to a photomultiplier tube (PMT) via an optical fiber. However, it is said that the light transmission efficiency in this technique reduces significantly depending on the transmission properties, particularly on the critical angle of the optical fiber. We performed experiments and Monte Carlo simulations to examine the extent of the decrease in the light transmission efficiency of a discrete γ-ray detector, which uses optical fibers for the connection of the PMT to a scintillator, relative to that of an integrated γ-ray detector, which connects the PMT directly to a scintillator. We also examined the effects of the reflection and connection materials on the light transmission efficiency. The results show that to improve the light transmission efficiency, it is useful to apply specular or diffuse reflectors appropriately to the side and bottom surfaces of the scintillator, and also to provide space (air layer) between the output surface of the scintillator and the input surface of the optical fiber without using grease.

The 6061-0 aluminum alloy sheet with two millimeter thick was welded by friction-stir-welding (FSW) at various welding conditions. Microstructure of the welds was investigated by optical microscopy in order to characterize the plastic flow pattern in the weld and change in size and morphology of the matrix grain structure from the original pancake-like structure in the parent sheet. The transverse cross section in the weld revealed that the boundary between the stir zone and the TMAZ (thermo-mechanically-affected-zone) exhibited a linear shape from the top to the bottom through the sheet thickness. An onion-ring pattern, which was common in the friction-stir-welded thick plate, was not detectable in the present stir zone. The wavy striations were observed in the transverse- and longitudinal-cross section of the weld. These were traces of the oxide films on the butt surface of the parent sheet and these provided the base for the evaluation of characteristic plastic flow in the friction-stir welded thin sheet. Yield strength and UTS of the weld were almost equivalent to those of the parent sheet. On the other hand, the reduced elongation was obtained. The weld was shown to break in the HAZ (heat-affected-zone).

We examined the effect of constraining the positron source lifetime parameter during a least-square fitting (LSF) of positron annihilation lifetime (PAL) data on the resultant lifetimes, as determined from the fit result. The effect was assessed using calculated PAL spectra and also experimentallyobtained spectra for single-crystal silicon with different measurement statistics, in order to discuss the uncertainty of the resultant lifetime for a sample having a relatively short lifetime of around 220 ps. The obtained results suggest that constraining the positron source lifetime during the LSF analysis results in a relatively minor uncertainty of the sample lifetime in comparison with that due to the measurement statistics.

In order to realize a commercial system with a user-friendly interface for positron annihilation lifetime (PAL) measurements, we have applied our previously developed anti-coincidence method to a compact system, controlled by dedicated software with a data analysis module. The functionality of the data-analysis code was confirmed by examining the reproducibility of input average lifetimes for calculated PAL histograms. A prototype for the commercial system was constructed and the validity of the analysis using the system was ensured by measuring a reference material.

Optimization of the measurement condition for positron annihilation lifetime spectroscopy (PALS) is discussed from the viewpoint of non-destructive "on-site" material inspection. Numerical analysis based on a least-squares estimation and experiments with various sizes of BaF2 scintillators by conventional PALS suggested that the use of relatively large BaF2 scintillators enables on-site material inspection by PALS with reasonable accumulation time and time resolution.

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).