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Aggregate centers in reactor irradiated single crystal a-,41,0, are investigated using the thermochemical and photochemical methods. Isochronal and isothermal annealing5 of the bands at 302, 356, 450, and 570 nm are performed in detail to study the thermal stability and to obtain the activation energy ( E ) for the decay of their corresponding centers. After X-ray irradiation at room temperature, a new band at 384 n m appears in the crystal irradiated previously by reactor radiation. From the thermochemical and photochemical properties as well ns from correlations of these several bands, i t is proposed tentatively that the 450 and 570 nm bands are attributed to the Fi type center, and the 302 nm band to the F, center.Mittels thermochemischer und photochemischer Methoden werden Aggregatzentren in Reaktorbestrahlten cc-Al,O,-Einkristallen untersucht. Isochrone und isotherme Temperungen der Banden bei 302, 356,450 und 570 nm werden durchgefiihrt, um die thermische Stabilitat zu untersuchen und die Aktivierungsenergie ( E ) fur den Zerfall ihrer entsprechenden Zentren zu erhnlten. Xach Rontgenbestrahlung bei Zimmertemperatur tritt eine neue Bande bei 384 nm in den vorher im Reaktor bestrahlten Kristallen auf. Aus den thermochemischen und photochemischen Eigenschaften sowie aus den Korrelationen dieser verschiedenen Canden wird vorlaufig angenommen, daB die 450 und 570 nm-Randen dem FS-Zentrum und die 302 nm-Bande dem F,-Zentrum zugeordnet sind.

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Chemiluminescence measurement is a very useful method for detecting molecules. This method has high sensitivity, good reproducibility and selectivity, quick response and good linearity over a wide concentration region. However, it is not convenient for continuous and long-term detection, because a supply of reactants to produce luminescent species through a chemical reaction is required. Although many investigations have attempted to improve these disadvantages since 1960 1-4 , a long-term stability of the sensitivity has hardly been attained. A new possibility of a CL-based sensor which does not require a supply of reactants was proposed by Breysse et al. in 1976. 5 They observed CL during the catalytic oxidation of carbon monoxide on a thoria surface. In 1990, we found that CL is observed during the catalytic oxidation of organic vapors on an alumina surface. 7 These phenomena can be applied to CL-based sensors. Various methods to detect organic vapors in air have been reported elsewhere. [8][9][10][11] In this paper, we deal with a method used to detect organic molecules, e.g. acetone and ethanol, dissolved in water using this sensor. We will describe the elementary working mechanism of the sensor and its working condition under which the response is quick and stable. Figure 1 shows a schematic diagram of the measuring system for a CL-based sensor. The CL-based sensor is made of a sintered layer of γ-Al 2 O 3 powder with a thickness of 0.5 mm. The pasty mixture of the powder and aluminum nitrate solution of 2 M was laid on a ceramic substrate (3 mm×1.5 mm), and then heated at 900˚C for 2 h. The sensor was heated by an electric heater made of Pt film laid on the reverse side of the substrate. The sensor was placed in a quartz tube having two bundles of Teflon tubes of 1 mm in diameter at both ends of the tube in order to keep the movement of the gas around the sensor in a laminar flow. A sample solution containing organic molecules was placed in a vaporizer kept at a constant temperature. The vapor was mixed with synthesized air (a mixture of 21% oxygen and 79% nitrogen). The mixed gas at atmospheric pressure flowed through the quartz tube and was removed by a diaphragm pump. The mean-flow velocity of the sample gas in the tube (v) was controlled by a mass-flow controller. The chemiluminescence from the sensor was measured by a photomultiplier through optical filters using a photon-counting technique. For the CL spectrum measurements, a spectrometer was used instead of these filters. The CL intensity at each wavelength was measured at a resolution of 10 nm. The concentration of the organic molecules in the mixed gas was monitored by a mass spectrometer through a differential evacuating system. The results of a catalytic reaction on the sensor were also detected by the mass spectrometer. A new method is proposed for recognizing organic molecules dissolved in water using a chemiluminescence-based sensor made with a γ-Al2O3 catalyst. When a mixture of air and organic molecules, e.g. ethanol and acetone vaporize...