Thin glass windows

In recent years the need has arisen for very thin glass windows capable of withstanding a vacuum yet thin enough to transmit a and jS particles. S. Rosenblum and R. Walen (1945) have described the following method for putting very thin windows into capillary tubing of up to 2 mm bore. The process is very simple but may require some practice before the precise conditions necessary for a satisfactory window are achieved. 

The K Series of Molybdenum.—The authors have also measured the emission and absorption spectra for the K series of molybdenum. The apparatus and method used are described in previous papers.7 A Coolidge tube equipped with a molybdenum target and an extra arm at the end of which happened to be a thin glass window served as the source of radiation. 

The end of the capillary tube is heated until the glass is soft, then before it has time to cool it is touched on to the surface of a thin bubble of glass and a slight suction applied. This forms the window into a concave shape and draws it slightly down into the capillary, whose ends then protect it from damage. The bubble of thin glass should be thin enough to show interference colours. These windows will stand a vacuum provided atmospheric pressure is on the concave side of the window. If they are subjected to a pressure difference in the other direction, failure occurs due to the reversal of curvature. 

Foil Foil is a thin, fragile, lead-based metallic tape that is applied to glass windows and doors. The tape is applied to the window or door, and electric wiring connects this tape to a control panel. The tape functions as a conductor and completes the electric circuit with the control panel. When an intruder breaks the door or window, the fragile foil breaks, opening the circuit and triggering an alarm condition. 

For measurements at temperatures other than ambient, cells with double walls, which can be thermostatted, are also available commercially. If measurements are required at temperatures between ca. —5°C and room temperature, the sample compartment of the spectrometer can be flushed with dry air or nitrogen to reduce condensation on the cell windows. Below ca. — 5 °C the windows can be covered with a thin polythene film, but measurements below —25 °C are very troublesome. The problems associated with low temperature spectroscopic measurements were solved by enclosing the cell in an air-tight box fitted with glass windows (Dadley and Evans, 1967). The box was so designed that it fitted into the spectrophotometer and the air inside the box was dried with phosphoric oxide which, it is claimed, stopped condensation even at temperatures as low as — 60 °C glass windows could be used because only absorptions above 380 nm were of interest. 

I adopted the first method using cylindrical gels with a few mm diameter and 10 30 mm long, which were attached to the end of a thin glass capillary and set in a rectangular culture tube filled with pure water. The axis of the cylindrical gel was kept nearly vertical. The culture tube had a pair of flat glass windows, through which the diameter of gel was measured in situ with a microscope as a function of temperature. 

A xenon lamp was used as light source that irradiated the thin falling films flowing through a quartz glass window in the reactor [317]. Thiourea in methanol was used to reduce the labile endoperoxide directly to the stable diol product. The yield of cis-2-... 

The crystal scintillator is usually made from cleaved, optically clear sodium iodide (Nal) activated with 1% of Tl. The crystals are hydroscopic and thus, they are usually sealed in a vacuum tight enclosure with a thin Be window in the front (x-rays entry window) and high quality optical glass in the back (blue light photons exit window). The crystal is usually mounted on the photomultiplier tube using a viscous fluid that minimizes the refraction of blue light on the interface between the crystal and the photomultiplier. 

Figure 8. In special RCA-thinned devices the silicon is etched to 10-pm thick and a 500-pm glass window is placed on the back side.

Radiolysis and Photolysis Techniques. The source of ionizing radiation was a 50-Kev. x-ray unit, operated at peak energy and 50-ma. current. The radiolysis vessels were spherical borosilicate glass flasks (1000 cc.) into which thin bubble windows were blown of thickness on the order of 20 mg./sq. cm. These vessels were fitted with calibrated volumes to facilitate determination of absolute yields. The majority of irradiations were conducted at a gas pressure of 357 mm. Hg, although several experiments at a pressure of 40 mm. Hg are also reported. Using a nitrous oxide dosimeter (15, 38) the dose rate for ethyl chloride at 357 mm. Hg pressure was determined to be 1.2 X 1018 e.v./min. 

The ferrous-exchanged zeoHte was transferred as a slurry in distilled water into a Pyrex glass Mossbauer sample cell under oxygen-free, nitrogen gas. The ceU had two very thin Pyrex windows separated by a 1 mm gap. The sample filled this gap after the excess water had been removed under vacuum. It is essential to keep the dry zeoHte free from contact with air or oxygen as some immediate oxidation to the Fe + state can occur. The thin windows of the cell aUowed some 40% transmission of the 14.4 keV y-rays to occur. The Mbssbauer spectrometer used and the complete experimental details are described in detail elsewhere [7]. 

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