Genichiro Wakabayashi

X-ray imaging using the thermoluminescent properties of commercial Al2O3 ceramic plates

This research demonstrated that commercially available alumina is well-suited for use in large area X-ray detectors. We discovered a new radiation imaging device that has a high spatial resolution, high sensitivity, wide dynamic range, large imaging area, repeatable results, and low operating costs. The high thermoluminescent (TL) properties of Al2O3 ceramic plates make them useful for X-ray imaging devices.

Absorbed dose estimation using LET dependence in glow curve of thermoluminescent phosphor Li3B7O12:Cu in therapeutic carbon beams

ABSTRACT A high temperature ratio (HTR) method has been proposed to correct the linear energy transfer (LET) dependence of thermoluminescent (TL) efficiency. To realize the use of the slab-type thermoluminescence detector (TLD) that based on the phosphor Li3B7O12:Cu for heavy charged particle beam, the HTR method has been considered. To improve the reproducibility of HTR, the slow heating rate method is introduced in this report and the coefficient variations of HTR decreased from 10%–20% to 8%. The relation between TL-efficiency, HTR, and LET for Li3B7O12:Cu was manifested and the TL-efficiency as a function of HTR was derived in an attempt to measure the absorbed dose without LET information. The feasibility of the HTR method in therapeutic carbon beams was evaluated by comparing the dose estimated by Li3B7O12:Cu and by an ionization chamber. The accuracy of dose estimation in carbon beams was improved by using the HTR method, but there is room for further improvement. The use of Li3B7O12:Cu in heavy charged particle beams can be materialized with further improvement of HTR sensitivity.

Thermoluminescent responses of Li3B7O12:Cu to proton beam

A thermoluminescent (TL) phosphor Li3B7O12:Cu was irradiated by a proton beam at NIRS-HIMAC in Japan. Irradiation was performed at different water-equivalent depths using range shifters made of polymethyl methacrylate. The thermoluminescent responses of Li3B7O12:Cu were analysed, focusing on the TL efficiency and glow curve. The irradiated samples were heated from room temperature to 200°C at 0.16°C s(-1). The high-temperature area of the glow curve under proton irradiation changed in comparison with that under (60)Co gamma-ray irradiation. The relative TL efficiency of the main peak slightly varied between 0.8 and 1.1. The relationship between the relative TL efficiency of the main peak and the high-temperature area ratio (HTR) value, the relative TL ratio of the main peak to the high-temperature area, showed approximate linearity for proton dosimetry. Using correction based on the HTR method, the TL phosphor Li3B7O12:Cu can become a useful dosimetric tool for therapeutic proton beams.

Time Trend Change of Air Dose Rate on Paved Areas in Fukushima City After the Fukushima Daiichi NPP Accident

The Kinki University Atomic Energy Research Institute investigated radioactive contamination resulting from the Fukushima Daiichi Nuclear Power Plant accident in urban areas of Fukushima City, Fukushima Prefecture, Japan. Activity measurement of the surface soil and a survey of the dose rate distribution in urban areas were performed. From the results of this research, dose rate changes in paved areas became clear, and gradients of the dose rate decrease for different paving materials were measured and analyzed.

Recent activities in the field of radiation measurement and nuclear data

The Journal of Nuclear Science and Technology covers a variety of subjects in the field of radiation measurement and nuclear data. This summary introduces recent activities and unique works presented in recent years. Following the Fukushima Daiichi nuclear power plant accident, a lot of efforts have been continuously put in the development of radiation detectors and simulations for use in environmental monitoring and decontamination. The efficient method for the Monte Carlo simulation to calculate the dose rate from a uniformly contaminated ground [1] and the simplifiedmethodwith imaging plates to measure radioactive caesium concentrations in contaminated soil [2] were presented as rapid communications in the journal. In the field of radiation applications, the increase of radiation exposure to a patient in diagnostic technology has become one of themajor concerns. For example, computed tomography (CT) is widely utilized as a powerful diagnostic tool all over the world and the number of examinations with CT is continuously increasing. The radiation dose to visual organs by a head CT scan was evaluated with a mathematical head phantom and the efficient way to reduce the dose by using an eye shield was analyzed [3], because a head CT scan gives a relatively high radiation dose to visual organs despite their high radiation susceptibility. A unique idea to reduce the radiation dose as well as the risk of a side-effect by the use of an iodine contrast agent in contrast enhanced CT was presented in the series of intensive works [4–7], in which a set of several segmented detectors aligned with the direction of the incident X-rays, tansXend detector, is used for themeasurement of theX-ray energy distribution. Another unique application in the field of radiation measurement presented in the journal is a land mine detector system using capture γ -ray detections by neutron capture reactions with nitrogen and hydrogen [8].

Preliminary design study of a simple neutron energy spectrometer using a CsI self-activation method for daily QA of accelerator-based BNCT

ABSTRACT For recent boron neutron capture therapy (BNCT), accelerator-based neutron sources have been actively developed in place of reactor-based neutron sources. In this study, a novel neutron energy spectrometer for the daily quality assurance (QA) of BNCT was designed on the basis of a CsI self-activation method for accelerator-based neutron sources. The spectrometer design was optimized in terms of its energy resolution. To verify its applicability to high-intensity BNCT neutron fields, some practical simulations were performed. It was shown that the designed spectrometer was able to evaluate a neutron energy spectrum in approximately 900 s after an instantaneous neutron irradiation. In addition, its energy resolution was sufficient for detecting an unexpected distortion in the spectrum. The results confirm that the designed spectrometer can be employed for the daily QA of BNCT to check that the expected spectrum remains unchanged.

Migration of Radioactive Cesium to Water from Grass and Fallen Leaves

The TEPCO Fukushima Daiichi Nuclear Power Plant accident in March 2011 led to high amounts of emitted radioactive Cs being deposited on land by both rainwater and snowfall. In addition, a significant amount of Cs was deposited on the surface of leaves, and after the accident, both trees and grasses absorbed radioactive Cs through their roots. In order to assess the effect on water sources, it is therefore important to evaluate the amount of radioactive Cs migrating to the water from both grass and fallen leaves.

Study on Radioactive Cesium in Wild Mushroom

2011年 3月 11日の東日本大震災に伴う東京電力福島第 1 原子力発電所の事故によって、大量の放射性セシウムが大 気中に放出された、その一部は現在も福島県の浪江町、飯 舘村、南相馬市、川俣町などの地面に沈着しており、近畿 大学は震災直後から原子力研究所を中心として、川俣町に おける環境放射線の調査を川俣町と共同で行い、実態の把 握と対策の提言に資するデータの収集を行っている 。一 方、2012年 12月の朝日新聞の記事によると、青森県で採 取したきのこからも放射性セシウムが検出されたとしてい るが、検出された放射性セシウムは Cs-137のみで Cs-134 はなかったとしており 、事故後においても東北地方北部 で採取される野生きのこには、福島第一原発事故ではなく、 チェルノブイリ事故によってもたらされた放射性セシウム が検出されている可能性が高い。しかし、これまでに川俣 町の環境調査で測定された放射性セシウムとしては、Cs134も含まれていたことより 、検出された放射性セシウム は福島第一原発の事故により放出され、環境中に残留して いるものであることが強く示唆されている。 福島第一原発の事故以来、きのこは放射性物質の移行係 数が高い食品であるとの風評が流れたこともあり、特に野 生きのこや野外で栽培されているきのこは放射性物質濃度 が高い食品であるとされ、採取や販売が規制されてきた。 しかし、実際にはきのこの種類によっては放射性物質の濃 度は異なってくるといった研究報告 や、栽培方法の検 討により、野外で栽培されるきのこでも基準値以下に放射 セシウム濃度を低減した栽培法が開発されてきている に もかかわらず、いまだにきのこは放射性物質濃度、移行係 数ともに高い食品であると認識されている。また、マツタ ケやホンシメジのように植物の根に共生し、土から発生す る菌根性のきのこ (ectomycorrhizal mushroom; EM)は、シ イタケやエノキタケなどのように枯木や落葉から発生する タイプの腐生性きのこ (saprobic mushroom; SA)に比べて移 行係数が高く、高濃度の放射性物質を含むとため、食用に 供することができないとされている。 本研究では、福島県川俣町の計画的避難区域に指定され ている山木屋地区に自生しているきのこの放射能レベルの 研究論文

Evaluation of base materials of TL slab dosimeter for heavy-ion radiotherapy

In order to measure a three-dimensional dose distribution in X-ray radiotherapy, we developed TL slab dosimeter with new TL phosphor Li3B7O12(Cu), which has Zeff = 7.42 and a density of 1.01 g/cm3 and synthetic resin as binder [ 1]. We can measure a three-dimensional dose distribution easily and reliably using this detector. This detector showed a promising tool for QA/QC in advanced X-ray radiotherapies such as IMRT, etc. In heavy-ion radiotherapies which shape precipitous dose distributions, it is also necessary to measure three-dimensional dose distribution easily. To use TL slab dosimeter in heavy-ion dosimetry, it is essential to measure its LET dependence sufficiently. And it is necessary to evaluate the dosimetric water equivalence of this dosimeter for heavy ions. Previous studies showed that the relative TL efficiency of this TL phosphor decreased to ∼20% at the Bragg-peak of carbon 290 MeV/u beams and the stopping-power ratio of this dosimeter to water for carbon ions was 0.87 [ 2]. These results were not good for application in heavy-ion radiotherapy. It was often reported that there is a relationship between the glow curve shape of general TLDs (such as LiF and BeO) and LET. Using this relationship of glow curve and LET, the relative TL efficiency can be corrected and we could apply TLDs to dose measurement in heavy-ion radiotherapies. In this study, in order to develop better TL slab dosimeter for heavy-ion radiotherapy using TL phosphors with the above characteristics, we evaluated the dosimetric water equivalence of several base materials for TL slab dosimeter. We chose several kinds of ceramics with heating resistance as the base material; ISOPLATON E3, P1, M2, A98 S1 and Machinable Ceramics, TBS N64, N66, N1, N3 (ISOLITE Co., Ltd). We focused attention on stopping power, scattering power and nuclear cross-section of these materials for heavy ions. We calculated these interactions using the Bethe formula, the Gottschalk formula and the Sihver formula. Figure 1 shows the result of theoretical calculation of the water-equivalence ratio, stopping power ratio S/Sw, scattering power ratio T/Tw and nuclear cross-section ratio σ/σw for carbon-ion beam. In these ceramics, ISOPLANTON S1 was the best of base material for TL slab dosimeter for carbon-ion beam. On the basis of this evaluation, we will develop the TL slab dosimeter for heavy-ion radiotherapy. Fig. 1. Water-equivalence ratio of the base materials for TL slab dosimeter.

TheMo96(p⃗,d)Mo95reaction at50MeV

The {sup 96}Mo(p,d){sup 95}Mo reaction has been studied with a 50 MeV polarized beam. Differential cross sections and analyzing powers have been measured for investigating the level structure in {sup 95}Mo up to the excitation energy of 5.8 MeV. The standard distorted-wave Born approximation theory provides transfer angular momentum values and spectroscopic factors for the excited states. Furthermore, the theoretical analysis is extended also for the continuum region with a direct reaction model. Experimental double differential cross sections for continuum spectra are predicted well by adopting an asymmetric Lorentzian form for the response function in the distorted wave Born approximation based cross section calculations.