International Journal of PIXE

The amount of contaminated soil with radioactive cesium (Cs) is more than 22 million cubic meters as a result of the Fukushima Daiichi nuclear power plant accident. In order to save the cost for keeping the soil covered, it is necessary to reduce its volume. To seek methods of efficient volume reduction, we investigated the cross-sections of contaminated soil particles using autoradiography (ARG), SEM, particle-induced X-ray emission (PIXE) analysis. The results of ARG showed that the radioactive Cs atoms were distributed on the surface of contaminated soil particle. PIXE analysis showed that K, Fe and Ti were distributed also on the surface of contaminated soil particle. Therefore, it is considered that the radioactive Cs contamination correlated with the distribution of K, Fe, and Ti. Moreover, the result suggests that it is possible to reduce the volume of contaminated soil by peeling off the radioactive Cs contaminated surface of soil.

We succeeded in observation of ferrokinetics in a plant (20 days radish) using the micron RI imaging which was previously developed in our laboratory, by improving two criteria: (i) adjustment of the iron solution for the plant’s intake; and (ii) measurement of the radioisotope, ⁵⁵Fe in the course to take up solution in the plant. The accumulation of iron atoms in the plant was confirmed by the micro-PIXE and an appropriate density of iron was determined. Under an optimal condition of iron solution containing ⁵⁵Fe, the ferrokinetics in the plant was investigated by use of the micron RI imaging system.

We developed a standard-free method for untreated hairs and the method has been applied to quantitative analysis of more than 30,000 hairs taken from the people concerned in order to evaluate exposure to some toxic elements and intakes of essential elements. Besides these analyses, we have measured nearly 2000 hairs collected from healthy people in Japan over the past 20 years. It was found that concentrations of some elements, such as vanadium, chromium, manganese, copper and mercury, keep increasing up to the present. Such tendencies were particularly notable for female, while not clearly observed for male. Concentrations of some essential elements, such as calcium, magnesium and zinc, show no obvious long-term variations. On the other hand, iron and selenium show slightly decreasing tendencies. With regard to toxic elements, it was found that arsenic, chromium and mercury are tending to increase year by year.

A standard-free method for untreated hairs has been applied to quantitative analysis of the hairs taken from 1256 healthy people living in the Iwate prefecture, Japan. It was found that there are clear sex-specific differences in the concentration of some elements. Concentrations of many essential elements, such as calcium, magnesium, iron, copper, zinc and bromine, are clearly higher for female. In particular, calcium concentration is 2.6 times higher for female in comparison with that for male. Contrarily, concentrations of some toxic elements such as chromium, arsenic and mercury are higher for male. On the other hand, concentrations of many elements vary with age. Those of calcium, magnesium and zinc start to increase in the middle of teens and reach maximum in the middle of twenties for female. Mercury concentration increases as the ages advance, while those of chromium, arsenic and lead show no clear changes with age.

The nanoparticles, which releases anticancer drug with response to radiation, were developed. Also, two categories were tested: (i) their ability to release anticancer drug in vitro; and (ii) their kinetics in the body, when they were injected through tail vein of BALB/c mice in vivo. To prepare the particles, hyaluronic acid and protamine were mixed into carboplatin solution, and reacted for 30 min in room temperature. Those particles were exposed to a single dose of 10 Gy of 140 KeV X-ray. Their ability to release carboplatin with response to radiation was expressed as the percentage of ruptured particles, basing on images of particles, using micro PIXE camera. The amount of released carboplatin was measured by quantitative PIXE method. The kinetics of particles in body was assessed by counting the number of particles, which were trapped in lungs, using micro PIXE camera. The mean diameter of particles was 743 ± 34 nm. By irradiation, 59.3 ± 7.23% of particles ruptured, and 95.9 ± 2.3% carboplatin was released from particles. The trapped particles in lungs were significantly reduced, when compared with previous alginate-hyaluronic particles.

This paper discusses a method to directly observe the dose distribution around a syringe-needle-type proton-induced monochromatic X-ray source proposed to avoid the risk that could exist in conventional brachytherapy. Images taken by using liquid scintillator and a high sensitivity CCD camera are presented and the dose distribution is qualitatively evaluated by comparing it with a Geant4 Monte Carlo simulation result.

We studied feasibility of detection of a gap which is located across a beam track by measuring low-energy (63–68 keV) photons generated by beam irradiation. An experiment was performed with the Heavy Ion Medical Accelerator in Chiba (HIMAC). A ¹²C beam having 290 MeV/u was injected on a target consisting of two acrylic blocks. These two blocks were placed with a 10 mm gap along the beam axis. A detection system consisting of a semiconductor detector, a lead collimator having a slit, and borated polyethylene blocks was placed on a movable stage to detect low-energy photons emitted perpendicularly to the beam axis. The position of the detection system was moved at 2 mm intervals along the beam axis. It was found that the yield of 63–68 keV photons was clearly correlated with the position of the detection system. The position at which the yield curve had the lowest value agreed with the gap position. We also confirmed that the experimental result was well reproduced by a Monte Carlo simulation that includes generation of secondary electron bremsstrahlung.