Some toy badges that we obtained emitted fluorescence strongly, when there were irradiated by an ultra violet lamp in a darkroom. They were left on X ray negative films for several hours and one of them blackened films. Owing to these facts, we doubted if it is a radioactive material. In order to search if it is a radioactive material or not, a portion of the badge paint was examined by a liquid scintillation analyzer and an ammeter which is connected to a photo diode. Consequently, the badge paint was not identified a radioactive material. Then, to find the reason why some badges emitted under an ultra violet lamp and one badge paint blackened X ray negative films, neutron activation analysis was applied to the badge paint sample. As a result, we finally found that the badge paint was made of phosphorescent phosphor because it contains aluminum.
The effect of the weak leakage magnetic field on the response of a scintillation survey meter for125I is studied. The counting rate and the magnetic flux density are measured on the planes above the surface of an analog meter. The meter produces the weak leakage magnetic field. With the presence of the magnetic field, the counting rate for background radiations increases, whereas that for radiation from125I decreases considerably. The spectra of these radiations are observed to be shifted to the lower energy side. An amplification factor of the photomultiplier tube connected with the scintillator is reduced by the magnetic field. The variation of the counting rate is therefore ascribed to the shift of the spectra. When the main part of the spectrum enters the window set by the single channel pulse height analyzer of the survey meter, the counting rate increases. On the other hand, when the part leaves the window, the counting rate decreases. These results show that when radioactive contamination is checked with the scintillation survey meter, it is necessary to be more careful about the effect of the leakage magnetic field.