A New Precision X-ray Spectrometer

Abstract

Multiple-deep-slit x-ray spectrometer.—A Bragg spectrometer was provided with two collimators, each consisting of a number of thin parallel strips of lead, separated a distance 1/166 times their length so as to produce many deep parallel slits. By this construction, radiation from a considerable area of the target passes through one or other of the slits of the first collimator, a large area of the specimen is thus irradiated, and also reflected radiation passing through one or other of the deep slits of the collimator fastened to the ionization chamber reaches a large area of cross section of that chamber; therefore the intensity of the ionization is relatively much greater than for the ordinary spectrometer. Any type of flat specimen can be studied, since in the large area irradiated properly oriented crystals are sure to be present, for some angles at least. The intensity curves obtained show sharp peaks, therefore lines can be accurately measured even when only 2′ of arc apart. Moreover, the large intensity available enables such peaks to be located for large angles between the axis of the collimators, increasing the accuracy. A test with a small sheet of steel gave accurate measurements of the $\mathrm{MoK}{\alpha }_1$ and $\mathrm{K}{\alpha }_2$ peaks, the wave-length ratio coming out 1.00604 in agreement with Duane's value 1.00605. Also the expansion of the steel to 475°C was readily observed, the shift of 9′ giving a coefficient of 12 × ${10}^{-6\mathrm{}}$. The change in atomic distance produced by stretching a steel strip beyond its elastic limit was also measured, the contraction at an angle of 82° to the stress being 0.265 per cent. This instrument should prove useful in studying the effect of any agency tending to change the interatomic distances.