High-radiation-exposure tasks in Korean pressurized heavy-water reactors.

This study analysed the occupational dose in Korean pressurized heavy-water reactors (PHWRs) and identified tasks involving high radiation exposure. The average individual dose was sufficiently low to be below the annual effective dose limit for radiation workers and is even lower than the dose limit for the general public. However, some workers received relatively higher doses than others. Furthermore, most PHWR workers are exposed to radiation during planned maintenance periods. In this study, the radiation dose was normalized (radiation dose per unit time) to determine the high-radiation-exposure tasks in Korean PHWRs. Consequently, end-fitting lapping, delayed neutron tube work and fuel channel fixed-end change tasks were identified as high-radiation-exposure tasks in Korean PHWRs. If appropriate radiation protection measures are prioritized for the identified high-dose exposure tasks, optimization of radiological protection will be effectively achieved by reducing the dose that is relatively higher than the average.

Quasi-phase-matched third harmonic generation in organic multilayers.

We report the first realization of quasi-phase-matched (QPM) third harmonic generation in isotropic polymer films. Spin-coated thin films of ethyl-violet molecules dispersed in a polymer host (EV) were used as cubic nonlinear optical media because of their transparency at both the fundamental (1230 nm) and the third harmonic (410 nm) wavelengths. A passive layer of a UV-curable material was formed to compensate the phase shift between the two light waves after propagating through each EV layer. We fabricated a series of samples with 1~4 EV layers (0~3 alternatingly coated passive layers). The third harmonic output power showed a quadratic increase with the number of layers, providing a strong evidence for successful quasi-phase-matching. A conversion efficiency of 0.15% was observed with a 190 fs pulse input.

Wavelength measurement by Fourier analysis of interference fringes through a plane parallel plate.

When a diverging laser beam passed through a plane parallel glass plate, interference fringes were observed; analysis of these fringes provided accurate estimation of the source wavelength. The fringes had a unique angular range of uniform fringe density. Fourier transform of the fringes in this range directly provided wavelength information. Reference lasers were used to establish a calibration between the fringe density and wavenumber, with which we estimated the wavelength of a test laser. An accuracy of 4.5×10-5 was obtained, which is better than that of conventional grating spectrometers, while providing a much broader free spectral range. Our method has unique features, such as extreme simplicity of the setup, fast analysis, and low cost, which are great advantages in practical wavelength meter applications.

Measurement of thickness profiles of glass plates by analyzing Haidinger fringes.

We report what we believe is a novel method for measuring the thickness profiles of plane parallel plates by analyzing their Haidinger fringes. When an extended monochromatic source is viewed through a ∼1-mm-thick plate, concentric transmission-type Haidinger fringes can easily be observed. Small variations in the plate thickness result in changes in the radii of the ring fringes. In this study, we scanned 20-mm-diameter fused silica and BK7 plates while tracing a specific ring in each fringe pattern to measure the thickness profiles of the plates, achieving an uncertainty of 2 nm in the measurements of the thickness differences between two locations on each plate.

Surgical removal of endovascular stent after migration to the right ventricle following right subclavian vein deployment for treatment of central venous stenosis.

Central venous stenosis or occlusion occurs in 11-50% of hemodialysis patients with prior subclavian vein cannulation and ipsilateral fistula or shunt. Most patients are asymptomatic but some require treatment to reduce the risk of thrombosis and improve inadequate hemodialysis pressure. In these cases, endovascular intervention, including ballooning and stenting, is a feasible strategy for selected patents. We report an unusual case of a 40-year-old man on hemodialysis that underwent endovascular stenting to treat right subclavian vein stenosis and experienced stent migration to the right ventricle, requiring surgical removal.