K series of X-rays

In these equations the first members consist of several terms. In each case the first term is very much larger than the sum of all the others. For example, in the K series of X-rays, the sum of the es for all the lines in the other series amounts to less than 20% of the value of e for the Ca line. In the case of the Kfi line, the sum of the e s other than the Kfi amounts to only about 3.4% of the Kfi. For the 7 line the sum amounts to a small fraction of 1% of the Ky. We see, therefore, that we may write the approximate equations... 

The value of C, as has been explained, depends upon the nuclear charge less the screening effect of other electrons. For the K series of X-ray frequencies it varies nearly as Z. As the degree of ionization of the atom increases with more intense methods of spectral excitation, for example, passage from flame spectra to spark spectra, G increases. For the spectrum of ionized helium (nuclear charge 2, one electron) it is four times the value for hydrogen (nuclear charge... 

Fig. 18. Production of x-ray fluorescence K and E series from molybdenum atom.

The energy E of the characteristic X-rays within a given series of lines, i.e. Ka, K/J, etc., increases regularly with the atomic number Z. This dependence is called Moseley s law of X-ray emission ... 

Moseley found that each K spectrum of Barkla contains two lines, Ka and K(3, and that the L spectra are more complex. Later important work, especially by Siegbahn,38 has shown that M, N, and O spectra exist and are more complex in their turn. Relatively numerous low-intensity lines are now known to exist in all series. Fortunately, the analytical chemist can afford to ignore most of these low-intensity lines in his practical applications of x-ray methods at present. It generally suffices for him to know that x-ray spectra at their most complex are enormously simpler than emission spectra involving valence electrons, and that most x-ratr lines are satisfactorily accounted for on the basis of the simple selection rules that govern electron transitions between energy states. 

K EDGE ABSORPTION SPEGTRA. The absorption of x-rays in the vicinity of the K absorption edge of transition metals gives information on both oxidation state and coordination geometry of the central absorbing atom. The energy positions of various absorption features have been demonstrated to be correlated to the formal valence of V in an extensive series of oxides, vanadates and intermetallics (13"). 

The line is marked X in plate 4. In this plate the P lines correspond to an exposure of 33 V2 hours, whereas the 8 and y lines correspond to only 10 horns exposure. There is no known x-ray line belonging to any chemical element that could lie in its first-order reflection at the position marked X. In the second-order reflection one of the P lines of cerium might lie at X. The wave-lengths of these cerium lines are not sufficiently well known to enable us to tell whether the X line is a second-order reflection of cerium Pu or not. If it is cerium Pu it should be accompanied, theoretically, by another line close to it, cerium ft. Fiulher, if this is cerium ft the two a lines in the K series of cerium should appear in their second-order reflections close to the Mo K a lines. Experiments are in progress to test the radiation for the K ai and 2 lines of cerium reflected in the second order. If they really exist they should be easily detected, and, if they are not detected, the X line cannot be due to the radiation from cerium, but must be a new line. 

As mentioned in the introductory section, the liquid structure of benzene at 25°C which was very similar to that in solid was demonstrated by means of X-ray diffraction. Moreover, an exciton state in liquid benzene was predicted on the basis of the similarity of the absorption spectrum in liquid phase to that in solid crystal K series on S -Sg... 

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