L. S. Birks

A Geiger Counter Spectrometer for X‐Ray Fluorescence Analysis

A Geiger counter spectrometer was constructed for analysis of x‐ray fluorescence spectra. The instrument is capable of measuring the K series lines of the elements beginning at about atomic number 22, up to about atomic number 50. In the middle portion of this range, spectro‐chemical analyses can be performed rapidly with a sensitivity of 1 part in 10,000. Although the intensities are considerably reduced, analyses may still be carried out, using the L series spectra of the elements above atomic number 55.

Convex Curved Crystal X‐Ray Spectrograph

The convex side of a curved crystal will diffract a continuous range of x‐ray wavelengths simultaneously. Thus, it is useful for spectral analysis of flash x‐ray tubes or plasmas where there is not sufficient time to scan through the spectrum with a spectrometer. It is also convenient for detecting impurities in x‐ray targets and could be used for x‐ray spectrochemical analysis. The choice of analyzing crystal, the particular diffracting planes, and the orientation of the bending axis allows a considerable versatility in intensity and dispersion including the recording of two or three separate spectra in a single exposure.

Electron Probe X‐Ray Microanalyzer

A 1–3 micron electron probe of simplified design has been constructed for x‐ray spectrochemical analysis of metallic and nonmetallic specimens. At operating conditions of 20–30 kv and less than 0.1 microampere beam current, counting rates of about 3000 counts per second are obtained from pure elements such as iron; thus compositions as low as a few tenths percent are detectable. At increased voltage and current and with a beam size of 10–20 micron, counting rates may be increased to 50 000 counts per second. Applications include analysis of inclusions in metals and minerals, mass transfer material from liquid‐metal cooling systems, phase composition, and intermetallic diffusion studies.

Apparatus for Vacuum X‐Ray Fluorescence Analysis of Light Elements

Air absorption in the conventional x‐ray fluorescence analysis equipment limits detection to elements heavier than calcium. To avoid absorption of the longer‐wavelength x‐rays from lighter elements, a vacuum system, or one filled with H2 or He, is required. A vacuum apparatus has been developed for the analysis of elements from magnesium to titanium. It contains the x‐ray tube for exciting fluorescence; a specimen holder for six specimens; a collimator to limit the fluorescent radiation to a parallel beam; and a single‐crystal, Geiger counter spectrometer to analyze the radiation. A pressurized, double‐film, nitrocellulose window is used for the Geiger counter because the usual mica windows are opaque to radiation from elements lighter than sulfur. For calcium Kα, the increase in intensity resulting from evacuating the chamber is 100‐fold, with far greater increases for the lighter elements. Alkali halides and gypsum were tested as analyzing crystals. An application of the equipment to the measurement of ...

A High Temperature X‐Ray Diffraction Apparatus

An apparatus is described for heating an x‐ray specimen to 1200°C in vacuum while its diffraction pattern is being recorded continuously on a Geiger counter spectrometer. The heater consists of a length of 0.030‐inch tungsten wire embedded in beryllium oxide, the whole enclosed in a polished tantalum case. Either a flat metal sheet, or powder packed in platinum gauze mounted on sheet metal is suitable as a specimen. An area about one centimeter square in the center of the specimen is irradiated by the x‐ray beam in the focusing type of spectrometer. The temperature is uniform over this area to ±5 degrees centigrade. Two concentric radiation shields reduce heat loss. The outer shield also acts as the vacuum‐tight body of the oven and has beryllium windows to pass the x‐rays. Results indicate that rapid structure changes may be observed as they occur with this apparatus.

Thickness Measurement of Thin Coatings by X—Ray Absorption

A method is described for determining the thickness of thin coatings on crystalline bases by means of an x‐ray source and a Geiger counter, both situated on the same side of the coating. The x‐rays pass through the coating and are reflected at a Bragg diffraction angle from the base, back to the counter, their intensity being reduced by absorption due to the double transmission through the coating. The thickness of the coating is computed from the measured absorption. The method is applicable to coating thicknesses in the range 10−5 to 10−2 centimeter.

Calibration of rare‐earth x‐ray intensifying screens in the 15–70 keV energy range for use on pulsed x‐ray sources

Rare‐earth screens (Rarex types B and BG) were calibrated against Kodak No‐Screen x‐ray film using pulsed x radiation. Type B screen, which contains only an yttrium compound, is over 50 times more sensitive than No‐Screen film in the energy range above 17 keV and is the preferred screen, of the two tested, in the energy range below 50 keV. Type BG screen, which contains yttrium and gadolinium compounds, is 1.5 times less sensitive than type B below 50 keV (the Gd absorption edge) but 3.5 times more sensitive above 50 keV. All of the calibrations were accomplished with monochromatic x rays from secondary fluorescers. The results should be accurate for pulses of shorter duration than 1 msec, which is the decay time of the screens.

Compact Curved-Crystal X-Ray Spectrometer

A curved‐crystal spectrometer has been designed with all the mechanism except the crystal and detector arms contained in a box 6×7×3½ inches. Three sets of arms are provided for focusing circles of 10‐, 20‐, and 40‐cm radius. Either automatic drive at from ½ to 8 degrees 2θ per minute or manual scanning may be used. Precision‐cut commercial gears result in accurate positioning and less than 0.01° 2θ backlash in the drive mechanism. Thus the spectrometer is satisfactory for use with rather perfect crystals such as quartz as well as with the alkali halides. Interchange of crystals and alignment of new crystals is simple and rapid.

APPARATUS FOR X-RAY DIFFRACTION STUDIES OF METALS UNDER CONTROLLED STRESS AT ELEVATED TEMPERATURE

A Geiger‐counter x‐ray spectrometer was constructed for the dynamic study of phase changes and other phenomena in metals under controlled stress conditions at elevated temperatures. Temperature could be controlled from room temperature to the melting point of steel, and stress was independently varied from zero stress to the breaking stress of stainless steel. Applications included isothermal and athermal transformation studies under tensile stress in pearlite, bainite, and martensite.