The L spectra of iron, cobalt, nickel, and copper

Abstract

The elements iron, cobalt, nickel, and copper in the solid state are interesting in a number of ways. They are adjacent elements at the end of the group for which the M IV, V level is incomplete; the first three are ferromagnetic; their X-ray present abnormalities; and the critical potentials of their soft X-ray emission are strangely numerous and difficult to interpret. These properties are to be associated with the electrons at or near the surfaces of the atoms, and the study of the outer electronic energy levels is therefore of importance. For such a study soft X-ray spectroscopy is especially suited. In the experiments to be described a plane grating has been used in the grazing incidence position. This method of diffraction, whilst giving a dispersion inferior to that of the crystal, yields good intensity and seems preferable for the examination of weak diffuse radiations. The immediate objects of experiments were (i) to find whether the M levels and the abnormally separated L II and L III levels are dependent upon the ferromagnetic condition of the metals; (ii)to observe whether the anti-cathodes when heated and free from oxidation give the same results as previous workers have obtained when using cold anti-cathodes; and (iii) to ascertain whether, as suggested by the critical potentials, there exist radiations other than the normal L lines and satellites already observed. 2—Description of Apparatus The spectrograph which has been used is fully described elsewhere. The soft X-ray beam from a slit of mean width 0·065 mm passed through a second slit of the same width and fell on a plane glass grating at a grazing angle of about 1°. The grating was from the Siegbahn engine. The rulings, 1·2 cm long, extended for only 3 mm. The X-ray beam, after diffraction at the grating, fell almost normally on a plate 50 cm away. The optical system, mounted on a rigid bench, was housed in a steel cylinder evacuated by a Gaede diffusion pump. The X-ray tube was directly connected to the end of the spectrograph chamber, and was evacuated by a separate diffusion pump. It was separated from the spectrograph by a slit about 1 mm wide. This slit, while not interfering with the optical arrangement, considerably reduced the rate of diffusion of gases into the X-ray tube. The tube, made of quartz, was of the hot cathode type, the filament being in the form of a spiral about ½ cm long. The voltage was supplied by a D. C. generator capable of yielding 5000 volts.