Dose reduction using bismuth shielding during paediatric CT examinations in Slovakia

Considering the massive increase of computer tomography (CT) examinations in Slovakia during the last 10 y, it can be expected that a higher radiation load may be observed in the Slovak population. Since child population is more sensitive to radiation than adult population, a monitoring has started to see how high the radiation dose is for paediatric patients during CT examinations in chosen departments in Slovakia. The CT examination of the head is one of the most frequently done examinations in Slovakian departments and that is why measurements were done to clarify how usage of bismuth shields for eyes and thyroid can affect the eye and thyroid doses. For simulation, 215 thermoluminescent dosimeters were exposed on anthropomorphic phantom of a child with and without usage of bismuth shields. The result was that only two of the three chosen departments confirmed a reduction. On the other hand, one of the departments confirmed that the reduction can be up to 56-65 %, which is significant.     

Simulation of memory behaviour of a non-volatile Si3N4 structure containing si nanocrystals

Memory hysteresis, memory window and charge retention behaviour of an Al/Si3N4/Si structure with Si nanocrystals embedded in the Si3N4 layer are studied by fitting the results of a computer simulation to the experimental ones using simple analytical expressions. It is concluded that the current through the control nitride layer during a charging voltage pulse is higher than the steady-state current. At high voltage pulses other effects, as transients, additional current mechanisms or charge injection and trapping from the metal side, has to be considered. It is also obtained that the retention behaviour of the structure were determined by the Fowler-Nordheim tunneling.     

Electrical and memory properties of Si3N4 MIS structures with embedded Si nanocrystals

Memory structures with an embedded sheet of separated Si nanocrystals were prepared by low pressure chemical vapour deposition using a Si3N4 control layer and different Si2O2 or Si3N4 tunnel layers. It was obtained that Si nanocrystals improve the charging behaviour of the MNOS structures. Memory window width of 1.3 V and 2.0 V were obtained for pulse amplitudes of +/-9 V and +/-10 V, 100 ms, respectively. The extrapolated memory window after 10 years is about 15% of its initial value.     

Determination of carbon monoxide concentration and total pressure in gas cavities in the silica glass body of light bulbs by FT-IR spectrometry

Fourier transform infrared (FT-IR) spectroscopy has been adapted to control the quality of light bulbs made from silica glass. Such light bulbs contain a molybdenum accessory which, if contaminated with carbon, during the melting procedure of bulb fabrication, can cause the production of carbon monoxide. This CO can be trapped in small gas cavities in the silica glass body of the bulb. A method has been developed for the detection of CO and the total pressure within these gas cavities by traditional FT-IR spectrometry using a spectral resolution of 0.5 cm(-1). The concentration of CO was determined by using a classical least-squares (CLS) method, and the accuracy of concentration determination is reported for the case with sample and reference spectra recorded at different pressures. The total pressure in the cavities was established by two different methods: either by CLS fitting of reference spectra to sample spectra or fitting a Voigt line shape function to the spectral lines within the CO fundamental stretching band. In the latter method, the width of the lines was determined and pressure-broadening coefficients are given and compared with high-resolution data from the literature. According to the measurements, 0.55-0.80 atm total pressure and 0.8-4.0% (v/v) CO was determined in the gas cavities. This method can also be applied to determine the total pressure in similar enclosed spaces in which an appropriate indicator gas component exists.