The measurement of absorbed dose is vital technique for the quality assurance in gamma-ray and electron beam irradiation facilities. An exact dose evaluation is essential for optimization of the radiation effect. This report outlines various applications for dose ranges, the kind of dosimeters for the measurement of absorbed dose more than 1 Gy in radiation facilities and the dosimeter’s application. The international trends and the future subjects in high dose measurement are also described in this report.

Members of the International Plant Protection Convention, including Japan, carry out plant quarantine under international rules in order to protect the agriculture and forestry of their own countries and other countries, and to prevent the invasion and dispersion of quarantine pests that adversely affect them. This paper outlines the mechanism of plant quarantine and the phytosanitary actions in Japan and the method of disinfecting pests adhering to imported and exported agricultural products, that is, the irradiation treatment schedules among the international standards for phytosanitary measures.

In Japan, food irradiation is generally banned under the “Food Sanitation Law.” On the other hand, food irradiation is approved for use in various countries for the purpose of microbial decontamination, phytosanitary treatments, sprouting inhibition etc. Since imported irradiated food violates the law, detection methods for irradiated food have been needed in monitoring inspections for imported food in Japan. This section describes outlines of detection methods introduced in Japan and the monitoring inspections for irradiated food using these detection methods in Japan.

Visualization of beams in particle therapy is useful to eliminate deviations of the irradiation area and to improve treatment outcome. In this study, we propose a beam imaging method using bremsstrahlung as an indicator and imaging plates (IP), which are widely used in the field of radiological diagnosis. We succeeded in obtaining high-resolution beam images through the IPs and indicated that the estimation of the carbon beam range was possible with the accuracy of the standard deviation of 2.5 mm.

External exposure to veterinary staff and pet owners from ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG, dose 170±33 MBq/head) in veterinary nuclear medicine was measured by monitoring the surface (SDR) and ambient dose rates (ADR) from animal patients (dogs and cats). The patients’ weights ranged from 4.2 to 32.3 kg (11±9.4 kg). The highest SDR was at the ventral abdomen, and its SDR time course was within the degradation curve with a physical half-life (109.8 min). ADR demonstrated a significant decrease up to approximately 30-to 80-fold by keeping a 100-cm distance from the patient. The estimated occupational radiation dose from the FDG injection before sedation was higher than the dose received from the FDG injection after general anesthesia. All patients showed acceptable SDRs, which was less than 3.8 µSv/h at 24 h post-injection, where cumulative SDR until infinity was less than 1/100 of the limit of the yearly external public exposure (1 mSv/year) which recommended in ICRP publication 103. According to the current legislation in Japan, these results represent an overregulation of detention 24 h after FDG injection in the case of an adequate lower maximum SDR.

Tracer experiments using radioisotopes (RI) are highly quantitative, sensitive, and have the advantage that the elements themselves are tracers. Our recent works on ⁴²K and ¹³⁷Cs tracer experiments have characterized the root uptake and translocation of radiocesium in plants in comparison with potassium. In the ²²Na tracer experiment, we are continuing to develop new methods to analyze the function of sodium transporters. In recent years, the number of experimental materials has been increasing at an accelerating rate along with the progress of genome science, and it is important to develop RI-tracer experimental methods that can meet the needs for analysis of these materials.

[¹⁷⁷Lu]Lu-oxodotreotide is a peptide receptor radionuclide therapy (PRRT) agent. The concentration of radioactive materials in the air was measured on patients during treatment with this drug. The concentration of lutetium (¹⁷⁷Lu) in the air was below the detection limit in the administration room and the waiting room, while it was detected in some cases in the special measures patient room. However, the detected levels were well below the concentration limits on radioisotopes specified in the second column of Appendix 3 of the Ordinance for Enforcement of the Medical Service Act.

Targeted alpha therapy is attracting significant attention for the treatment of intractable tumors and the development of efficient gamma cameras to evaluate the biodistribution of alpha emitters is expected. ²¹¹At, which is a commonly used alpha emitter in Japan, emits characteristic X-rays whose energy is distributed between 77 and 92 keV. We evaluated the biodistribution of this alpha emitter by effectively acquiring these photons. Because the performance of a gamma camera strongly depends on that of collimators, we designed and manufactured high-performance collimators by processing pure tungsten, which can shield radiation more effectively than lead, using state-of-the-art three-dimensional (3D) printing technology. We successfully fabricated a parallel-hole collimator with a honeycomb structure with a hole size of 1.0 mm and septal thickness as thin as 0.07 mm. When a point source of ¹³³Ba that emits photons with the energy of 81 keV, similar to that of characteristic X-rays emitted from ²¹¹At, was imaged using this collimator, spatial resolution of this collimator was as short as 5.7 mm and its efficiency was as good as 1.42×10⁻⁴; these results are superior to those of commercially available clinical scanners. We also demonstrated that our collimator could successfully depict a shape of the object by imaging a mouse thyroid gland after the injection of the ²¹¹At solution. These results suggest that excellent collimators made of pure tungsten could be used to monitor targeted alpha therapy using ²¹¹At.

We have conducted a radioactive survey of sake for tritium, which is the isotope of hydrogen with low β-ray energy and is considered difficult to detect and remove. Using a differential-type magnetically levitated electrode ionization chamber (MALIC) developed by Kyushu Sangyo University, we had previously measured gaseous radiation dose (ionization current) for tritium vapor. Based on the result, we analyzed Fukushima specialty sake to determine the radioactive materials and estimated the radioactivity concentration of tritium in sake. As a consequence, our device enabled direct detection at the Japanese drinking water standards level. Besides, we confirmed that the radioactivity concentration of this sake was quite far below the lower limit of the Japan and WHO drinking water standards.

Radioisotopes have been widely used in various life science researches such as medicine and agriculture. We have produced useful radioisotopes for the abovementioned purposes, including positron-emitting copper-64 and bromine-76, and alpha-emitting astatine-211, by using an AVF cyclotron in QST-Takasaki. The author describes the outline of research on production (irradiation and isolation), labeling method, and imaging or therapeutic studies of these useful radionuclides.

Tin nanoparticles were synthesized by chemical reactions induced by irradiation. γ-ray irradiation of aqueous solution of SnCl₂ resulted in the formation of metallic Sn nanoparticles. It was indicated that Sn²⁺ions are reduced to zero valence by radiochemical species generated by the irradiation. On the other hand, SnO₂ nanoparticles were obtained when irradiated in the presence of carbon support. Small metallic Sn nanoparticles were well dispersed on the surface of carbon support which are assumed to be easily oxidized to form SnO₂ nanoparticles. It was indicated that nanoparticle synthesis techniques using radiation is applicable to form tin.