Hiroko Ohuchi

Measurement of Highly Tritiated Water by Imaging Plate

Abstract Concentration of tritium in highly tritiated water was measured by exposing imaging plates (IPs) to water vapor. Tritium penetrated into photostimulated luminescence (PSL) phosphor through polyethylene terephthalate protection layer, and well detectable signal of PSL was induced at tritium concentration of 16 kBq cm-3. In addition, tritium was reversibly desorbed by keeping IPs in air, and signal from IPs returned to background level. In other words, IPs exposed to tritiated water vapor were reusable; tritium concentration in water could be measured without any waste. In addition, no handling of tritiated water such as sampling and dilution was necessary.

Compton spectroscopy for rotation-mode computed tomography

In computed tomography (CT) systems, it is desirable to know the X-ray energy spectra for various applications, including medical CT imaging, and diagnostic field and heavy ion therapy. However, because of the restricted space, the only practical solution is to use Compton spectroscopy, where the incident spectrum is inferred from the scattered spectrum. The geometry of the scatterer and its position within the CT can affect the spectrum of the secondary beam, making it difficult to determine the primary spectrum during operation of the CT system. A modified Compton spectrometer is described that allows measurement of the X-ray energy spectra during operation, and most importantly, in rotation mode. The geometry of the scatterer was optimized to reduce the energy broadening of the secondary beam. The performance of the system was evaluated by comparing the reconstructed exposure to that measured directly using an ion chamber.

Tritium Measurement in High Gamma-Ray Radiation Fields by Using an Imaging Plate

Abstract An imaging plate (IP) was applied to measure tritium in high 60Co gamma-ray radiation fields. The IP made of europium-doped BaFBr(I), a photostimulated luminescence (PSL) material, is a two-dimensional radiation sensor. The PSL response of the IP has a peak at 20-50 keV and steeply decreases towards higher energy, falling by one hundredth at around 1 MeV. By utilizing a large difference in the PSL response to photon energy between 60Co (1.173 and 1.333 MeV) and tritium (maximum energy of 18.6 keV), the bremsstrahlung X-ray induced by tritium beta ray was detected in mixed radiation fields with tritium and 60Co, varying 60Co dose rate in the range 0.0013 to 9.22 μGy/min. It was found that the effect of 60Co irradiation to PSL value, obtained by irradiated with tritium of 12.5 MBq, was negligible by dose rate of 4.38 μGy/min and there was only 7.0% difference of PSL value, obtained by irradiated with tritium of 100 MBq, between dose rate of 0.0013 and 9.22 μGy/min. The IP tritium measurement method can be a promising candidate to measure tritium in high gamma-ray radiation fields.

Complete erasing of ghost images caused by deeply trapped electrons on computed radiography plates

The ghost images, i.e., latent image that is unerasable with visible light (LIunVL) and reappearing image appeared on computed radiography (CR) plates were completely erased by simultaneous exposing them to filtered ultraviolet light and visible light. Three different types of CR plates (Agfa, Kodak, and Fuji) were irradiated with 50 kV X-ray beams in the dose range 8.1 mGy to 8.0 Gy, and then conventionally erased for 2 h with visible light. The remaining LIunVL could be erased by repeating 6 h simultaneous exposures to filtered ultraviolet light and visible light. After the sixth round of exposure, all the LIunVL in the three types of CR plates were erased to the same level as in an unirradiated plate and no latent images reappeared after storage at 0°C for 14 days. The absorption spectra of deep centers were specified using polychromatic ultraviolet light from a deep-ultraviolet lamp. It was found that deep centers showed a dominant peak in the absorption spectra at around 324 nm for the Agfa and Kodak plates, and at around 320 nm for the Fuji plate, in each case followed by a few small peaks. After completely erasing CR plates, these peaks were no longer observed.

Tritium measurement using a photo-stimulable phosphor BaFBr(I):Eu2+ plate

Abstract Tritium measurement is indispensable for the fuel- processing systems of deuterium-tritium (DT)-fusion facilities. A new approach to detect tritium in regions deeper than the escape depth of beta-rays from tritium is being developed using an imaging plate (IP). The measurement principle of this approach is to observe bremsstrahlung X-rays induced by the tritium beta-rays. An IP made of europium-doped BaFBr(I), a photostimulated luminescence (PSL) material, is a two-dimensional radiation sensor. In the present study, the characteristics of this IP for measuring tritium by detecting bremsstrahlung X-rays, in particular a fading effect and the energy dependence of PSL sensitivities, are examined.

Adapted erase method using ultraviolet light and the influence of ghosting image on a clinical CR image

In Storage Phosphor (SP) used for Computed Radiography (CR), the quite stable latent image remains due to impurities and the lattice imperfections by the existence of trapped electron and hole. The quite stable latent image appears again (Ghosting image) by the passage of time etc, is recognized as image, and becomes an artifact in a clinical CR image. This study verified the influence of Ghosting image on a clinical image by a physical characteristic and the subjective evaluation, and examined the method to delete this artifact by the exposure of ultraviolet light as a method of improving image. As a result, Ghosting image can be confirmed by the dose used by the clinical diagnosis study, and it is taken as deterioration of the granularity on a physical characteristic. The decrease of the granularity of about 15% (by winner spectrum) was admitted by the frequency band of 2cycle/mm in SP that had been used for a long term. As the method of improving these, Ghosting image was erased with the ultraviolet light lamp with the peak wavelength at 310nm, and has band from 290 nm to 320 nm, and is useful for the improvement of the image quality. In this study, we examine the influence of Ghosting image on a clinical image, and report on the method to delete them by the exposure to ultraviolet light radiation for the image quality improvement plan that uses the x-ray used for usual clinical diagnosis study.