[en] Industrial radiography is known to be one of the most vulnerable lines of work among the range of different radiation work. According to the relevant law in Korea, every worker registered in this work should check their blood cell counts every year in addition to their thermoluminescent dosimeter (TLD) doses. Cytogenetic dosimetry has been employed for several decades as a method for estimating the dose of ionizing radiation (IR) received by an individual. In cases of recent acute exposure, the most reliable method is to score dicentric chromosomes in solid-stained metaphase cells. Dicentric aberrations are unstable because their frequency decrease with time after IR exposure. The purpose of the present study was to review the effectiveness of the current regulation that requires all registered radiation workers to check their blood counts every year in order to screen for exposed workers. In addition, the clinical usefulness of cytogenetic dosimetry as a retrospective tool for dose estimation has been evaluated. From this study, we hope to make practical recommendations for improving the current radiation protection regulation. We ascertain that reviewing consecutive results of blood cell counts and retrospective biodosimetry are useful complementary tools to TLD doses for health protection regulation. Several confounding factors including work duration and previous medical history need to be considered for the interpretation of cytogenetic dosimetry results.

[en] The effects of inflow pulsation on the flow characteristics and mixing properties of turbulent confined coaxial jet flows have been studied. Large eddy simulations were performed at Re = 9000 and the mean velocity ratio of the central to annular jet, U_i/U_o, was 0.6. Pulsation was generated in the inflow jet by varying the flow rates. First, inflow pulsation was applied at frequencies in the range 0.1 < St < 0.9 while other parameters were fixed. The pulsation frequency responses were scrutinized by examining the phase- and time-averaged turbulence statistics. The pulsation frequencies St = 0.180 and 0.327 were found to produce the largest enhancement in mixing and the largest reduction in the reattachment length, respectively. The effects of the phase difference between the two inflow jets at these two optimal frequencies were then investigated. The optimal phase difference conditions for mixing enhancement and the reduction in the reattachment length were obtained when the strength of the outer vortices was high. Further, we found that the strength of the inner vortices was reduced by varying the phase difference, and the reattachment length was minimized, and that if the strength of the inner vortices was increased, mixing was enhanced.

[en] Two cases of hematological malignancies were reported in an industrial radiography company over a year, which were reasonably suspected of being consequences of prolonged exposure to ionizing radiation because of the higher incidence than expected in the general population. We analyzed chromosomal aberrations in the peripheral blood lymphocytes from the other workers who had been working under similar circumstances as the patients in the company. Among the subjects tested, 10 workers who belonged to the highest band were followed up periodically for 1.5 years since the first analysis. The aim of this study was to clarify pertinence of translocation analysis to an industrial set-up where chronic exposure was commonly expected. To be a useful tool for a retrospective biodosimetry, the aberrations need to be persistent for a decade or longer. Therefore we calculated the decline rates and half-lives of frequency for both a reciprocal translocation and a dicentric chromosome and compared them. In this study, while the frequency of reciprocal translocations was maintained at the initial level, dicentric chromosomes were decreased to 46.9% (31.0–76.5) of the initial frequency over the follow-up period. Our results support the long-term stability of reciprocal translocation through the cell cycle and validate the usefulness of translocation analysis as a retrospective biodosimetry for cases of occupational exposure. (author)