Visual comparisons between Cherenkov radiation from water and fluorescence from a scintillator.

A system for observing blue light of Cherenkov radiation was constructed using a Co-60 gamma-ray irradiation unit. However, there was some doubt that the observed light was not Cherenkov light, but scintillation. Therefore, the radiation from water was compared with that from a scintillator. The difference between both luminosities was examined using photographs taken in a dark irradiation room with mirrors and a camera. The radiation from the scintillator was much stronger than that from water. The differences between luminosities of the light radiated in the beam direction, at right angles to the beam and in the reverse beam direction were examined for both radiations. The luminosity from water showed very definite anisotropy, while that from the scintillator was almost isotropic. Furthermore, the light radiated in the beam direction from water was the strongest, and the strengths of the light radiated in the three directions from the scintillator were almost equivalent to each other. It was confirmed that the radiation from water irradiated by Co-60 gamma-rays was indeed Cherenkov light. The anisotropy of the radiated Cherenkov light and the isotropy of the scintillation were clearly observed in the photographs.

A method for measuring the dose distribution of the radiotherapy domain using the computed radiography system.

Knowing the dose distribution in a tissue is as important as being able to measure exposure or absorbed dose in radiotherapy. Therefore, we have developed a measurement method for the dose distribution (CR dosimetry) in the phantom based on the imaging plate (IP) of the computed radiography (CR). The IP was applied for the dose measurement as a dosimeter instead of the film used for film dosimetry. The data from the irradiated IP were processed by a personal computer with 10 bits and were depicted as absorbed dose distributions in the phantom. The image of the dose distribution was obtained from the CR system using the DICOM form. The CR dosimetry is an application of CR system currently employed in medical examinations to dosimetry in radiotherapy. A dose distribution can be easily shown by the Dose Distribution Depiction System we developed this time. Moreover, the measurement method is simpler and a result is obtained more quickly compared with film dosimetry.

[Observation of Cherenkov Radiation from Aquarium Irradiated with Co-60 Gamma-rays]

Cherenkov radiation in water at a nuclear power plant is caused by a nuclear fuel rod and is well known generally. If students can observe Cherenkov radiation at school easily, they can be impressed by the fascinating radiation. Moreover the observation may bring about interest in radiological physics profoundly. A few years ago, management of the Co-60 gamma-ray irradiation apparatus was transferred to Nagoya university school of health sciences from the related hospital. Therefore we have examined the system to observe the Cherenkov radiation in water from secondary electrons generated by Co-60 gamma-rays. At first, the Cherenkov radiation in the aquarium was led to the corridor outside the irradiation room using a mirror, and observed directly while avoiding exposure. Secondly photographs of the Cherenkov radiation from various angles were taken under conditions which consisted of several irradiation fields and pass lengths of gamma-rays in water, and were compared with each other. Our method for observing the Cherenkov radiation may be useful enough for students to raise their dedication in radiological physics study.

Evaluation of Linearity for the Radiophotoluminescence Glass Dosimeter Based on Monochromatic X-rays.

Although low energy X-rays have been utilized for mammography, their safety in medical use is a matter of concern. Characteristics of the radiophotoluminescence glass dosimeter, GD-403, consisting of a glass element and filters, were investigated with respect to monochromatic X-rays obtained from a synchrotron radiation for personal monitoring of low energy photons. We focused on low energy X-rays ranging from 8 to 20 keV to study the linearity of the GD-403 response between photon fluence and dose equivalent. The GD-403 was placed on a tough water phantom and irradiated using an 11-15 mm x 0.1-7 mm beam for modulation of the photon fluence. The tough water phantom could be moved through a distance of 110-150 mm with a stepping motor. For the dose equivalent at 1cm depth (H1), 3mm (H3) and 70 &mgr;m (H70), the GD-403 showed sufficient linearities against the photon fluences in the energy regions of 8 to 20 keV, 13 to 20 keV and 13 to 20 keV, respectively. However, H3 and H70 did not provide sufficient linearities in the energy region of 8 to 12 keV. Moreover, we compared the result in this experiment with the value calculated from the absorbed dose of air using the mass absorption coefficient for the X-ray energy ranging from 10 to 20 keV.