Abstract
IN previous papers (Comptes rendus, 182, 1083, and 183, 193, May and. July 1926) a method was given, suitable for spectrographic work in the unknown region between 20 and 150 Ångström units. In the meantime, some Kα lines belonging to light elements (oxygen, carbon, boron), and a few N barium lines, have been measured. It was interesting to apply the new method to the detection of lowest frequency N and O series of a heavy element. Thanks to the kind help of Dr. Holst, Director of the Philips Laboratory, I obtained a sample of thorium wire, prepared by Dr. de Boer, and I used it as a hot cathode in the X-ray tube of my vacuum spectrograph. With an exposure of 4 hours, with a current of 29 milliamperes under 2.8 kilowatts peak value, I obtained good thorium spectra. The middle part of each plate is covered by a filter consisting of goldbeater's foil, 7 × 106 cm. thick, used to estimate penetrating power and order of spectra. All the lines detected are new N and O thorium lines of very low frequency. A very strong 45.3 Å.U. line coincides with the Kα line of carbon, but is a different one. This is proved by three facts : that tantalum, molybdenum or zir conium hot-wire cathodes, used in the same conditions, do not show the carbon line; that the thorium deposit on the target was very important and visible to the naked eye; that measurements of critical potentials, made with another apparatus, by the ionisation method, do not show at all the carbon K critical potential (287 volts) but the two well-defined N3 (355 volts) and N12 (312 volts) thorium critical voltages, corresponding to the respective emission of 45.3 and 51.5 ÅU. lines.
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DAUVILLIER, A. Spectrographic Junction between the X-ray Region and the Extreme Ultra-Violet. Nature 118, 551 (1926). https://doi.org/10.1038/118551a0
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DOI: https://doi.org/10.1038/118551a0
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