No abstract

Tellurium suboxide thin films TeOx were found to change in refractive index and extinction coefficient on thermal or optical heating, with accompanying changes in the reflectivity and transmission. The preparation method and thermal or optical properties of the TeOx thin films were investigated to obtain a stable and highly sensitive optical disc memory. A two-source evaporation method using Te and TeO2 provided uniform and any desired composition. The properties of the film depended on the x value; increasing x to as large as x=1.2, which represents a Te-poor composition, produced an excellent humidity and heat stability, and decreasing x to 0.8 made the film more sensitive to a laser diode, but susceptible to humidity. The TeO1.1 thin film was found to sufficiently satisfy all requirements for practical disc applications. A reflective optical disc was prepared using the TeO1.1 thin film deposited on a polymethylmethacrylate substrate with grooves for optical tracking. This disc is capable of recording video signals at real time by laser diodes. It showed no reflectivity changes on recorded or unrecorded areas and no sensitivity change to laser light after long term storage in high humidity and temperature.

The phosphor Li2B4O7: Cu (0.03% by weight) has an effective atomic number of 7.3, which is very similar to that of tissue (7.4). This suggests that the phosphor should have excellent properties for thermoluminescent dosimetry. The phosphor prepared by a sintering method shows two glow peaks composed of a dosimetric peak at 205 degrees C and a shoulder at 120 degrees C, and a broad emission band peaking at 368 nm. The material based on the stoichiometric compound of Li2O . 2B2O3 has a good moisture resistant property. The dosimetric characteristics are as follows: (1) The sensitivity of gamma rays is about 20 times higher than that of Li2B4O2: Mn prepared by the conventional melting method. (2) The dosimetry peak of 205 degrees C fades less than 9% in intensity at 25 degrees C after 60 days in dark. (3) The TL output is linear with exposure to about 10(5) R, becoming sublinear above it. (4) The sensitivity loss caused by humidity is about 10-25% after 2-6 months of storage in air of 90% relative humidity at 25 degrees C. (5) The energy dependence of TL output for photons is flat within the limit of 10% from 40 keV to 7 MeV. (6) The light induced fading is 10% after 3 h room lighting at 1000 lux.

AbstracCA composite thermoluminescent dosimeter (TLD), composed of four, thin TL elements with a high-speed reader, has been developed by employing an optical-heating method. Each TL element, which is 15mg/cm2 thick with a 3 m m dia., is prepared by applying Li2B407:Cu or CaS04:Tm to a plastic substrate 14 mg/cm2 thick. Each element can be heated to 350°C within 0.8sec. by IR radiation from a tungsten lamp. The characteristics of this TLD system include the following: (1) the detection limit of the Li2B407:Cu is 3 mR and the limit for CaS04:Tm is 0.1 mR; (2) the energy-dependence curves are similar to the doseequivalent curve, showing slight under-responses by 15% near 70 keV for Li2B407:Cu, and over-responses by 50% at high energies for CaS04:Tm; (3) despite quick heating, the residual dose is as low as 0.1% of the last exposure signal; (4) responses are very stable for more than 1 ,OOO cycles of repeated exposure readings; (5) no false signal could be detected, even in the cases of sweat or soil contamination; (6) the thin Li2B,07:Cu element can be used for skin dose monitoring; and (7) the processing time of the automatic reader for the composite dosimeter is 3 hr/SOO dosimeters. This TLD system can be applied to personnel dosimetry, gate monitoring and environmental monitoring.

Suboxide thin films of SbOx, TeOx, MoOx, and GeOx (x is smaller than the stoichiometric value for each component) were found to have the property of showing a critical change in their absorption coefficients and refractive indices at elevated temperatures. The thin-film samples were prepared by evaporating a mixture of the stoichiometric oxide powder and a deoxidization metal powder such as tungsten. The critical temperatures of these thin films are 150, 120, 150, and 280 °C, respectively. The absorption coefficients before and after the heat treatment are 2.5×104 (before) and 6.1×104 (after), 8×104 and 1.0×105, 5.6×103 and 1.1×104, and 4.9×104 and 1.8×105 cm−1, respectively. Their refractive indices are 1.8 (before) and 1.9 (after), 3.1 and 3.5, 1.8 and 2.1, and 2.5 and 2.8, respectively. As determined by x-ray diffraction analysis, these thin films are composed of very small metal grains and stoichiometric oxide grains. The thermal changes accompanied by the optical constant changes are mainly due to structural changes in the metal grains. These thin films are concluded to have the feasibility of application to optical disk memories of the laser heat-mode type.