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Luminescence of water during irradiation with particles having energies below the Cerenkov-light threshold was recently found for various types of radiations. However, the relation between the intensities of Cerenkov light and of the luminescence of water at the beam energy below the Cherenkov threshold is not well known. To clarify this point, we measured the produced light irradiating a water sample with electron beams having maximum energies above and below the Cerenkov-light threshold. The intensities of light during irradiation of electron beams with different energies increased rapidly at higher energy than ~260 keV while very small intensity was observed at the beam energy below the Cerenkov-light threshold. We conclude that the intensities of light produced in water during irradiation of electron beams with energies below the Cherenkov threshold from the luminescence of water are much lower than those of Cerenkov light.

Although light emission from an acrylic block during irradiations of carbon-ions lower energy than the Cerenkov-light threshold was found recently, the origins and fractions of the light in the images were not yet obvious. Since light spectra may provide information to estimate the origins and fractions of the light emission, we conducted the optical imaging of acrylic block during irradiations of carbon-ions using charge coupled device (CCD) camera with optical filters. We measured the light images of acrylic block with optical filters of different wavelengths using an ultraviolet (UV) sensitive CCD camera during carbon-ion irradiations with the energy slightly higher energy to produce secondary electrons to emit Cerenkov-light (241-MeV/u). From the images, we derived the depth profiles with different wavelengths and calculated the spectra of the emitted light from acrylic block. The depth profiles showed higher intensity due to Cerenkov-light at the shallow area distributed in the images of longer wavelengths. By the calculations between depth profiles of different wavelengths, we could derive the depth profiles for possible origins of the produced light: luminescence, Cerenkov light and scintillation of acrylic block. Using the derived fractions of these components, we could estimate the depth profiles of these three components with different wavelengths.

Astatine-211 is one of the promising radioisotopes for targeted alpha therapy. Optimising treatment strategies as well as determining the suitability of a given agent for a particular patient requires to image the time-dependent distribution of the targeted radiotherapeutic agent both in tumours and in normal tissues. Since the biodistribution of astatine is different from that of iodine, imaging astatine-211 directly is essential. In the previous study of astatine-211 Compton imaging, random coincidence events due to polonium K-shell X-rays were dominant and seemed to cause saturation of counts. Thus optimisation of the coincidence time windows is important to reduce random coincidence events. In this study, we have optimised the coincidence time windows of a Compton camera and improved the sensitivity, noise and spatial resolution of astatine-211 imaging.

Thesis (Ph. D. in Science)--University of Tsukuba, (A), no. 3011, 2002.11.30, Includes bibliographical references, "[208]" and "[209]" are superscript

Taking full account of nonparabolicity of a conduction-band dispersion, we investigate those electronic excitations in the conduction band of an n-type narrow-gap semiconductor which are coupled with polar phonons. By incorporating the nonparabolic dispersion obtained by a k⋅p method in a complete manner into the random-phase approximation, we calculate the energy dispersion and the energy-loss intensity of two coupled plasmon-phonon modes and a longitudinal optical-phonon mode partially screened by carriers. The results are compared with those of two simplified treatments, namely, one with the spin-orbit splitting neglected and the other assuming a parabolic dispersion of the conduction band with its effective mass modified. This comparison asserts that complete treatment of the nonparabolic dispersion is indispensible to quantitative analysis of the plasmonlike mode at higher carrier concentrations. Simultaneously, it elucidates limitations and shortcomings of the simplified schemes. The complete treatment of the nonparabolicity leads to an excellent agreement with the experiment on the carrier-concentration dependence of an intensity-vanishing point in the infrared-reflection spectrum.