The abnormal values of background count in liquid scintillation counting are sometimes caused by static electricity charged on a Teflon counting vial. The experiments were carried out by measuring the background sample in the Teflon vial repeatedly under various counting conditions. The spurious counts were observed in almost case at the beginning of measurement of background sample. These spurious counts couldn't be detected even if statistical analysis such as null hypothesis test is employed. Therefore the analytical results of tritium must be evaluated by taking account of the spurious counts. In addition, a substitute for a Teflon counting vial was selected to solve the above problem.
The effects of gamma-ray irradiation to a marine pennate diatom Phaeodactylum tricornutum were investigated. The diatom is rich in carotenoid pigments, fucoxanthin and β-carotene which are known to have antioxidative activity in vitro. The cell growth and the pigment contents were measured under various irradiation conditions. In every run, the algae grew 20 to 30 fold in 5 days after irradiation of up to 193 Gy, which was acutely fatal to animal body or cells. The cell growth and the pigment contents showed little differences between irradiated samples and its control when they were exposed to gamma-ray of up to 100 Gy for 12 min. But 60 min irradiation gave inhibitory effects on the cell growth and the fucoxanthin content decreased when 1.0 Gy dose was given. Conversely, low doses ranging from 0.2 Gy to 0.5 Gy did stimulate the cell growth compared to its control though the doses over 0.5 Gy showed inhibitory effects. In contrast to the cell growth, both the amounts and contents of β-carotene or fucoxanthin, however, considerably decreased under these low doses. Fucoxanthin decreased while β-carotene increased compared to the control when the algae was exposed to gamma-ray for 60 min with over 1.0 Gy. There was no significant correlation between the doses and β-carotene content below 1.0 Gy.
In radiotherapy due to administration of radionuclides, accurate estimates of three-dimensional (3D) absorbed dose distributions of target regions can be performed using a 3D dose matrix convolution method which has already been developed based on a voxel based calculation algorithm by the authors. The purpose of this study is to elucidate the influence of unit voxel sizes of cumulated radioactivity distributions of beta-emitting radionuclides on 3D absorbed dose estimates. Computer simulations were performed using cubic phantoms (24×24×24 mm, 32×32×32 mm, and 48×48×48 mm) and the MIRD thyroid phantom as the target regions assumed distributed uniformly for various beta-emitting radionuclides (32P, 90Y, 131I, 186Re, and188Re) . The maximum, mean and minimum absorbed doses for their phantoms comprised of various unit voxel sizes (1×1×1 mm, 4×4×4 mm, and 8×8×8 mm) were estimated using the 3D dose matrix convolution method developed. In the cases of the 3D cumulated radioactivity distributions of the target regions comprised of various unit voxel sizes were identical with one another, the maximum and mean absorbed doses for the target volumes were independent of the unit voxel sizes. However, as the unit voxel sizes were increased, the minimum absorbed doses were overestimated.
207Bi has been detected in a BGO scintillator by a Ge spectrometer. The concentration of207Bi was found to be 3.1 mBq/Bi-g. Metallic samples of pure bismuth, produced recently and commercially available also contain207Bi of 2 to 9 mBq/Big. A lead concentrate of PbS containing 0.30 % of bismuth and being a raw material of Bi metal has been measured for gamma-emitting radionuclides. An upper limit on the concentration was estimated to be 2 mBq/Bi-g Besides207Bi, the presence of a fission product, 137Cs, in the concentrate was examined. The possible origin and route of the207Bi contamination is discussed.