We have investigated the performance characteristic of the heavy metal filters with higher atomic numbers by comparing their patient exposures, tube loadings, radiographic contrasts, and noise Wiener spectra with those of a combination of copper and aluminum filter which has been used widely in chest radiography.
Seven heavy metal filters were used for this study. As for a tungsten filter, two filters different in thickness were used. One is 0.05 mm thick, and the other 0.10 mm. The other metal filters were respectively combined with a tungsten filter with a thickness of 0.05 mm.
Among the all filters investigated, tube loading of tungsten filter with 0.05 mm thick is minimum. Tungsten with 0.1 mm thick and tungsten with 0.05 mm + barium show the larger advantages in patient exposure than those of the other filters.
It was found that the magnitude of patient exposure varied slightly wit h the difference of image receptor used. The use of heavy metal filters showed the small advantages in the patient exposure reduction (-20%) compared with that of conventional copper filter. The use of heavy metal filters showed increasing tube loading (-5times) compared with that of conventional copper filter. Noise Wiener spectra of heavy metal filters showed comparable with those of conventional copper filter.
In conclusion, the use of heavy metal filter combinations offer no significant advantages over optimal conventional filters.

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The basic primary and scatter dose-spread kernels used for convolution methods are usually produced by Monte Carlo simulations with the interaction point forced to the center of a large water phantom. This paper proposes another type of basic kernel, with which perfectly accurate primary and scatter absorbed dose calculations can be performed within a semi-infinite water phantom under certain irradiation conditions.

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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.

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