A compound semiconductor, thallium bromide (TlBr), has been investigated as a radiation detector and photodetector material for use in X- and γ-ray spectroscopy. Single crystals of TlBr have been grown by the traveling molten zone method using zone-purified materials. The TlBr crystals have exhibited large mobility-lifetime products of 1-2 × 10^-4 cm²/V and 4-9 × 10^-5 cm²/V for electrons and holes, respectively. X- and γ-ray detectors have been fabricated from the TlBr crystals. An energy resolution of 30 keV FWHM has been recorded for 511 keV γ-rays with the TlBr detector at room temperature. Photodetectors for scintillation spectroscopy have been fabricated from the TlBr crystals by depositing a thin film of Au as an optically transparent electrode on the surface. Quantum efficiency of the TlBr photodetectors has been high in wavelength region below ～460 nm where scintillation emissions of LSO and GSO occur. The TlBr photodetector coupled to an LSO scintillator has exhibited an energy resolution of 34.5% for 511 keV γ-rays.

  Adler et al. developed an Image-guided frameless radiosurgery system in 1992. The CyberKnife is a X-band linear accelerator mounted on a robot, and is used for stereotactic irradiation. The CyberKnife is equipped with two fluoroscopic cameras, which constitute the Image Processing System (IPS). The patient's location can be determined precisely by comparing the digitally reconstructed radiograms (DRR), prepared from CT scans, with the real-time fluoroscope images. According to the information of the patient's location, the robot chases the moving patient. Therefore, patients can be treated without an invasive frame.

  In April 1998, a CyberKnife was installed at the Osaka University Hospital. We make it a rule at our hospital to perform a practice irradiation on the phantom before performing irradiation on each patient. The median total targeting error was 0.7 mm.

From April 1998 to December 2000, 43 sites in 28 patients with metastatic brain tumors were treated. There were 19 males and 9 females with a median age of 62 years ranged from 50 to 73. During these periods we carefully performed a dose escalation study. We adopted the single session of 9-20 Gy for group A, 24-25 Gy for group B and 27-30 Gy for group C as a standard dose for stereotactic radiosurgery.

There were 9 PR, one NC and 5 PD for group A, 3 CR, 7 PR, 2 NC for group B and 9 CR, 4 PR, 2 NC and one PD for group C. The median survival time was 4 months in group A, while it was 10 months for groups B and C. Dose escalation study using CyberKnife was feasible and effective for stereotactic radiosurgery for metastatic brain tumors.

  From December 1998 to December 2000, 18 patients with head and neck tumors of 19 lesions were treated using CyberKnife. There were 12 males and 6 females with a median age of 60 years ranged from 18 to 81. Primary sites were 7 nasopharynx, 5 oropharynx, 3 intraoral cavity, 2 maxillary sinus, and one middle ear. Most patients underwent 15 Gy/3 fractions for boost therapy to previously untreated lesions and 39 Gy/3 fractions for re-irradiation for recurrent lesions. One-year progression free survival rates was 72%. There were no adverse effects so far.

  The real time tracking system for CyberKnife has been realized with AccuTRack system using LED on the body surface and amorphous silicone detector system for metal marker inserted into the tissue in the vicinity of the tumor. This enables us to treat lung tumors that move with respiration. Tumors in the lower spine, pancreas, and lung have been treated with CyberKnife in the USA.

  We have been developing a high energy resolution x-ray microcalorimeter with an Ir TES film. First we fablicated an Ir-TES of 0.5mm×0.5mm. The measured energy resolution was 194eV (FWHM) for 5.9keV x-rays and this value is extremely worse than the theoretical resolution. We considered the limitation in the energy resolution arises from non-uniformity in the heat diffusion process and temperature distribution inside the TES. To improve the heat diffusion property, we have developed a new pixel geometry that has shorter length of electrodes and some thin slits to separate the heat diffusion area of the Ir TES. This device achieves an improved energy resolution of 47.0eV (FWHM) at 5.9keV. Furthermore the rise time and fall time map has shown the possibility of identifying the pixel position which would be useful for an imaging TES array.

  We suggest a method for the enlargement of the sensitive area of NIS tunnel junction detectors: connecting segmented absorbers to a common sensor via heat switches. Heat switches can control heat flow and can confine the volume of temperature rise.

  An application of a single electron transistor device is proposed to read out signals from super conducting tunnel junction radiation detectors with high sensitivity and good signal to noise ratio. Here are presented preliminary consideration on the device design and fabrication method.

  Bismuth tri-iodide (BiI₃) is an attractive material for fabrication of room temperature radiation detectors because of its wide bandgap energy and high photon stopping power. In this study, BiI₃ crystals have been grown using commercially available powder by the vertical Bridgman technique. The crystals have been characterized in terms of their structural properties and stoichiometry. Room temperature radiation detectors have been fabricated from the crystals and tested by measuring their leakage currents and spectroscopic responses. An energy resolution of 2.2 MeV FWHM for 5.48 MeV α-particles (²⁴¹Am) was obtained from a BiI₃ detector.

  Fiber Bragg grating (FBG) is a kind of an optical device developing rapidly in these years. FBGs have capability of multiparameter sensing at many points along a fiber. To assess the applicability of FBGs to nuclear plants, influences of jackets' degradation and temperature sensitivity in gamma-ray environment were investigated. It was shown that Bragg peaks were not shifted by gamma-ray and have no dependence on the existence of jackets. Moreover, temperature sensitivities of FBGs were not influenced by gamma-ray irradiation.

  Optic Data Link (ODL) is a device to convert electric and optic signals to each other, which is used for the field of optical communications. We examined the possibility to apply ODLs to radiation measurements. The effect of ODLs on energy and timing resolution has been investigated. From the results, fundamental applicability of ODLs to radiation measurements has been demonstrated.

  In resonance ionization mass spectrometry (RIMS) with a time-of-flight mass spectrometer (TOF-MS), some difficulties arise in an analysis of a very small amount of isotopes of interest through interference of secondary ions produced by collision of a large amount of resonant ions with reflectron and extraction electrodes and sometimes cluster ions produced under intense laser ablation of target materials, which have many kinds of mass/charge ratios. In this study, we have tried to overcome the above problem by replacing the TOF-MS to a quadrupole mass spectrometer (QMS). Here are presented the preliminary results obtained from basic experiments with a prototype QMS-RIMS.

  In this study, a CdZnTe (CZT) detector was employed as an x-ray spectrometer in the mammographic energy range. The major problems in x-ray spectrometry with CZT detectors have been spectral distortion due to transmission of primary x-rays, the escape of Cd-K and Te-K x-rays, and tailing. The distortion, however, proved to be minimal in mammographic x-ray spectrometry. The reasons for this were that the energy of x-rays used in mammography was quite low (～30 keV), and the average atomic number of CZT crystals was high (approximately 50). Therefore, correction for spectral distortion was not necessary when using CZT detectors in mammographic x-ray spectrometry. In addition, CZT detectors are compact because the detectors can be operated at room temperature: large detectors such as germanium detectors cannot be employed in mammographic x-ray units. We conclude that CZT detectors are suitable for x-ray spectrometry in mammographic x-ray units under clinical conditions.

  Recently, the researches on radiation hormesis toward the animals and plants are made abundantly. The radiation hormesis effect is that subharmful doses of radiation may evoke a stimulatory response in any organism. We did irradiation experiments of fusion (DD and DT) neutron, thermal and fast neutron, and 60-cobalt gamma-ray to the dry seeds of Raphanus stivus, and examined whether radiation hormesis effects appeared by measuring germination rate, the length of a hypocotyl and a root and the total weight on the 7th day from starting cultivation. The evaluation of radiation hormesis effects was done by using relative effectiveness which is the ratio of the mean of the measurement objects of the irradiation group to that of non-irradiation group. In the Raphanus stivus the radiation hormesis effects of the measured objects were only turned up in seed groups irradiated by the fusion (D-T) neutron. We have confirmed that absorbed dose range where the effects are revealed is from 1 cGy to 10 Gy and there the relative effectiveness is from 1.05 to 1.25. In this research the model about radiation hormesis effect on Raphanus sativus confirmed in irradiation of D-T neutrons is proposed. And it is apparent that radiation from radio activated seeds influences hormesis effect on Raphanus sativus.

  Pulsed X-ray irradiations on a mineral-insulated (MI) cable were carried out to investigate its electrical properties under irradiations. The transient reduction of the electric resistance induced by the pulsed X-rays was well observed by use of the pulsed-charge measuring system. The amount of charge induced in the central wire was approximately proportional to the bias voltage and the X-ray dose per pulse, which suggests that the production rate of charge carriers and their drift dominate the resistivity degradation of the MI cable. Numerical calculations on charge induced in the central wire were performed to examine characteristics of the drift of electrons in the insulator. Also, the relation between the leakage current and temperature was measured with a ⁶⁰Co gamma-ray source to examine the influence of temperature.

  An intense X-ray source using a laser light that was inversely Compton-backscattered with relativistic electrons has been used for nuclear physics study and for some industrial applications. Current status of the facility and some of the applications are briefly described.

  A laser-produced plasma (LPX) is a compact and brilliant x-ray source. Our study reported in this paper on x-ray microscopy, reduction lithography, and photoelectron spectroscopy shows that full utilization of LPX's advantages can realize performances never achieved by other x-ray sources. Extensive efforts of exploring x-ray applications and future further developments of laser technologies will open-up a new era of x-ray sciences.