Aerodynamic diameter and radioactivity distributions of radioactive aerosols from activated metals cutting for nuclear power plant decommissioning.

Radioactive aerosols from nuclear power plant decommissioning have not been actively studied compared to those from severe accidents. However, it will be more critical issues in the future. The radioactive aerosols will deposit on the surfaces of matter and disperse in the working space. Hence, the workers in nuclear power plant decommissioning may inhale some of the aerosols during the normal operation or accident. The health effects of aerosols depend not only on the particle size but also on the aerodynamic and thermodynamic characteristics. Therefore, it is crucial to understand the distribution of radioactive aerosols regarding their aerodynamic diameters, radioactive isotopes, and chemical forms to ascertain the respirable fraction. We analyze the effect of the cutting method, cutting material, and cutting conditions on the mass and radioactivity distributions of radioactive aerosols and identify the dominant factor for the safety of workers in the nuclear power plant decommissioning process. We confirm that the chemical composition and radioactive contamination in cutting material affect the aerodynamic diameter distribution and the amount of aerosol. Finally, we suggest the underwater plasma arc cutting process that could minimize the internal dose of workers at the nuclear power plant decommissioning sites.

Integral T-shaped phantom-dosimeter system to measure transverse and longitudinal dose distributions simultaneously for stereotactic radiosurgery dosimetry.

A T-shaped fiber-optic phantom-dosimeter system was developed using square scintillating optical fibers, a lens system, and a CMOS image camera. Images of scintillating light were used to simultaneously measure the transverse and longitudinal distributions of absorbed dose of a 6 MV photon beam with field sizes of 1 × 1 and 3 × 3 cm(2). Each optical fiber has a very small sensitive volume and the sensitive material is water equivalent. This allows the measurements of cross-beam profile as well as the percentage depth dose of small field sizes. In the case of transverse dose distribution, the measured beam profiles were gradually become uneven and the beam edge had a gentle slope with increasing depth of the PMMA phantom. In addition, the maximum dose values of longitudinal dose distribution for 6 MV photon beam with field sizes of 1 × 1 and 3 × 3 cm(2) were found to be at a depth of approximately 15 mm and the percentage depth dose of both field sizes were nearly in agreement at the skin dose level. Based on the results of this study, it is anticipated that an all-in-one phantom-dosimeter can be developed to accurately measure beam profiles and dose distribution in a small irradiation fields prior to carrying out stereotactic radiosurgery.

Development of a 2-channel embedded infrared fiber-optic temperature sensor using silver halide optical fibers.

A 2-channel embedded infrared fiber-optic temperature sensor was fabricated using two identical silver halide optical fibers for accurate thermometry without complicated calibration processes. In this study, we measured the output voltages of signal and reference probes according to temperature variation over a temperature range from 25 to 225 °C. To decide the temperature of the water, the difference between the amounts of infrared radiation emitted from the two temperature sensing probes was measured. The response time and the reproducibility of the fiber-optic temperature sensor were also obtained. Thermometry with the proposed sensor is immune to changes if parameters such as offset voltage, ambient temperature, and emissivity of any warm object. In particular, the temperature sensing probe with silver halide optical fibers can withstand a high temperature/pressure and water-chemistry environment. It is expected that the proposed sensor can be further developed to accurately monitor temperature in harsh environments.

A study on the cerebral sizes of Koreans in their 20S and 40S.

The purpose of this study was to measure the cerebral sizes of Korean adults in their third (20s) and fifth decades (40s) of life using Talairach-Nowinski reference points to determine the effect of sex and age on cerebral size and asymmetry. Magnetic resonance images of the brain of 94 adults between 20 and 29 years of age (43 males and 51 females) and 99 adults between 40 and 49 years of age (38 males and 61 females) were measured. The distance between reference points and cerebral size of males was greater than those of females. Cerebral width and the size of the left cerebrum of those in their 40s decreased more than those in their 20s. The effect of age on left cerebral atrophy of males was greater than that of females. Left cerebral size was greater than right cerebral size. There was no difference in cerebral asymmetry between the genders. Cerebral asymmetry of those in their 40s was smaller than of those in their 20s and the decrease of cerebral asymmetry of males due to age was greater than that of females. A positive relationship existed between cerebral height, and body height and weight for males in their 20s.