Junji Miyahara

A new type of X-ray area detector utilizing laser stimulated luminescence

Abstract A conceptually new integrating area (250 mm×200 mm or larger) detector system, originally developed for diagnostic radiography, has been used for synchrotron radiation experiments. In this detector system, an X-ray image is temporarily stored as a distribution of F-centers in a photostimulable phosphor (BaFBr:Eu 2+ ) screen. The stored image is read out by measuring the intensity of fluorescence ( λ ∼390 nm) stimulated by a Heue5f8Ne laser beam scanned over the surface of the screen. The detector has 100% detective quantum efficiency for 8–17 keV X-rays, a spatial resolution better than 0.2 mm (fwhm) in both directions, a dynamic range of 1:10 5 and no counting rate limitation. Diffraction patterns from muscle and a protein crystal were recorded in several tens times less exposure than that of high-sensitivity X-ray films.

Mechanism of photostimulated luminescence in BaFX:Eu2+ (X=Cl,Br) phosphors

Abstract In BaFX:Eu 2+ , the excitation by X-ray or ultraviolet light and the photostimulation of luminescence by visible light are caused by the processes of Eu 2+ ⇌Eu 3+ and F + -centers⇌F.

An imaging plate neutron detector

Abstract We have developed two kinds of imaging plate neutron detectors (IP-ND), where the neutron converters, 6 Li (tentatively, Nat Li was used) and Gd were mixed with photostimulated luminescence (PSL) materials on a flexible plastic support, and the dynamic range and spatial resolution of our IP-ND were successfully obtained as 1:10 5 and less than 0.2 mm, respectively, which are comparable to the ones of X-ray. The distinctive features of the IP-ND, where the IP-NDs of different neutron detection efficiency and converters were positively used, were found and discussed. The application of the IP-ND for neutron radiography was demonstrated.

Design and performance of an imaging plate system for X-ray diffraction study

A new readout system for a BaFBr: Eu2+ photostimulable phosphor screen (imaging plate) was constructed by modifying a drum scanner, with a design optimized for X-ray diffraction and scattering applications. An effort was made to achieve a high detective quantum efficiency below 20 keV, a small pixel size (25 μm × 25 μm), a low quantization noise (0.22%) using 12-bit A/D converters, and the capability to cover an inherent dynamic range (1:105) of the photostimulated luminescence by using two photomultiplier tubes. This system is being used in several synchrotron radiation experiments: Laue diffraction of protein crystals, small angle diffraction from a single muscle fiber, powder diffraction from crystals in a diamond anvil cell, and time-resolved small-angle X-ray scattering from a synthetic polymer during stretching.

Radioactivity distribution measurement of various natural material surfaces with Imaging Plate

Distribution images of natural radioactivity in natural materials such as vegetables were obtained by using Imaging Plate. In such cases, it is necessary to reduce background radiation intensity by one order or more. Graded shielding is very important. Especially, the innermost surface of a shielding box should be covered with acrylic resin plate. We obtained natural radioactivity distribution images of vegetables, sea food, meat etc. Mostly β-rays emitted from40K print the radioactivity distribution image. Comparison between γ-ray intensity of KCl solution measured with HPGe detector and that of natural material specimen gave the radioactivity around 0.06∼0.4 Bq/g depending on the kind and the part of specimens.

Effect of background radiation shielding on natural radioactivity distribution measurement with imaging plate

Abstract Distribution images of natural radioactivity contained in various natural materials such as vegetable, animal meat and pottery work can be obtained with an imaging plate which has high sensitivity for nuclear radiations. For such very low levels of radioactivity, natural background radiations must be reduced using a shielding box. The lining, on the inside of the box, with low atomic number material such as acrylic resin is very effective in reducing electrons, β-rays and low energy X- and γ-rays emitted from the inner surface of the shielding material. Some images of natural radioactivity distribution were obtained and the radioactivity, mainly 40 K, contained in natural materials was measured by using an HPGe detector and also the imaging plate itself.

CHARACTERISTICS OF PROMPT SCINTILLATION FROM IMAGING PLATE

Abstract Imaging plate emits “prompt luminescence” when a radiation enters. The ratio of photo-stimulated luminescence intensity from latent image to prompt luminescence intensity depends on the type and energy of incident radiations. The ratio is smaller for the radiation with larger stopping power such as α-particle.

Imaging Plate Detector In X-Ray Diffraction Using Synchrotron Radiation

An imaging-plate X-ray area detector which utilizes photostimulable phosphor (Ba FBr: Eu2+) originally developed for diagnostic radiography, has a detective quantum efficiency of more than 80 % for 8 ~ 20 keV X-rays, a 1:105 dynamic range, a spatial resolution of 150 μm full width at half maximum and no instantaneous count-rate limitation. A readout system for imaging plates has been developed for the purpose of X-ray diffraction studies by modifying a drum-type densitometer. Two apparatus for time-resolved measurements have also been developed. The first one is based on a cinema method which permits 40 exposures of a two dimensional X-ray pattern (100 mm x 108 mm) with a 0.3 s time resolution. The second one works as a 200 mm-long linear detector which enables a time resolution of 23 μs for a duration of 46 ms, based on a streak-camera method.

Radioactivity on the Experimental Notebook of Mme. Curie-Collection of Meisei University Library-

明星大学・図書館に所蔵されているキュリー夫人の実験ノートの表紙, 裏表紙, 等に付着している放射性物質の分布状態をイメージングプレートで測定した。また, α線の強度とエネルギースペクトルをシリコン検出器で, γ線スペクトルを高純度ゲルマニウム検出器で測定した。表紙, 裏表紙ともに, 手が触れる部分の放射能強度が強く, ノートの小口 (端) の部分にも付着していた。また, 多くの点状の汚染があり, 夫人の周辺には粉末状の汚染があったことが推察される。α線強度の測定によれば, 最も強く付着している部分においては, 我が国のα核種の表面密度限度 (4Bq/cm2) 以下ではあるが, それに近い値であった。α線及びγ線のエネルギースペクトルの測定では, 核種はウラン系列の226Raとその娘核種の壊変に伴うものであった。15年にわたる記入期間の各月ごとの記入ページ数を, 当時の状況を知る手がかりを得る目的で調べたが, このページ数には大きな変動があった。これらについて, 日本人研究者に関する事柄も記されている夫人の伝記を参考にして若干のコメントをした。

Flowers of Natural Radioactivity Observed with Imaging Plate.

イメージングプレートの放射線に対する高い感度, 潜像の蓄積効果を利用すれば, きわめて低レベルの自然放射能の分布の測定を行うことができる。しかし試料の自然放射能を測定するには, 試料以外からくる自然放射線を有効に遮蔽し, バックグラウンドレベルを減少させる必要がある。有効な遮蔽箱を検討し, その中で野菜等の植物, 動物などの生物体, あるいは陶磁器, 絵画等美術工芸品などに含まれている自然放射能の分布を測定した。このような分布は, 今までにない新しいイメージを与えるのみならず, 鉱物, 植物, 生物, 考古学等の各分野において有用な情報を提供する可能性がある。