In the nuclear-related public relation center, a variety of displays such as models of nuclear facility, panel presentations to explain radiation properties, radiation detectors are used for the visitors to help the understanding of nuclear power and radiation. The PR center demonstrates various aspect of the radiation such as the presence of natural background radiations around us in the daily life, shielding effect for the different kind of radiations. Cloud Chambers are often used to demonstrate the presence of natural background radiation, showing tracks caused by the ionizing effect. The shielding effect of radiation is demonstrated by inserting a shield material between a radiation source and the detector such as GM counter. It is usually illustrated in the panel that the penetration properties are different for kinds of radiation but actual demonstration is seldom used.
Then a question arises that people cannot properly understand overall characteristics of the radiation in the above described demonstrations in the PR center. So we have been trying to improve a utilization method of a cloud chamber to help the deep understanding of properties of radiation. The improved cloud chamber has the area size of 225 mm × 225 mm with 100 mm in depth and has the structure for the function of insertion and extraction of both a radiation source and a shield material, independently. When a radiation source such as Cs-137 or Fe-55 is inserted in the chamber, it is clearly shown that high energy electron created by gamma-ray or X-ray emitted from such radioisotope can make track with different length. It is also shown using lantern core with thorium-series isotopes that thick track can be made by alpha particle. Fe-55 radioisotope generates 5.9 keV X-rays, which produces about 1mm track in the chamber through photoelectron.
When a shield material of lead with a thickness of 1mm was inserted in front of the source, the fading out of the tracks is clearly observed. Thus shielding effect can be easily confirmed by eye using cloud chamber. The demonstrations of shielding effect described above can help more clear and essential understanding of the radiations. This was shown by the questionnaire survey done before and after the demonstrations for the 32 participants.
For further improvements of the cloud chamber, we are planning to enlarge the size of cloud chamber and to get much clearer track image by improving track illumination method. Finally we will re-consider more effective explanation to give correct understanding of the radiation and will verify the effectiveness of utilization method of new cloud chamber.