Determining the Wavelengths of -Rays Moseleys Law

When the wavelengths of the characteristic x-rays from sources consisting of various elements were compared, it became evident that the heaviest elements yielded x-rays of the shortest wavelengths. In particular, H. Moseley found that plotting the atomic numbers (Z values) of a number of elements against the square roots of the frequencies of a given type characteristic x-radiation (for example, Ka radiation) from each of these elements yielded a straight line. Moseley s relationship may thus be expressed  

The separations of the recently discovered elements hafnium (Z = 72) and rhenium (Z = 75) from immense quantities of ores were guided by x-ray spectra. Care must obviously be taken in such cases so that the investigator does not mistake a wavelength characteristic of a known element for one presumably arising from the new element. (The premature announcements of the discovery of elements 43 and 61 in nature were very possibly the results of incorrect assignments of lines in the x-ray spectra.) 

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