The soft X-ray absorption limits of certain elements

Abstract

According to Bohr’s theory of atomic structure, in the normal configuration of the electrons round the nucleus in any atom, each electron is bound so that its final orbit is that which is in most stable equilibrium with the nucleus and with the other electrons already bound, and the building up of a heavy atom is marked by periods at the end of which an electron group is completed. The orbits of the electrons in the different groups in the atom are characterized by different values of the principal quantum number n , and within each group the electrons are divided into sub-groups corresponding to different types of orbit characterized by different values of the azimuthal quantum number k . The more recent developments of Bohr’s theory attribute the long periods in the periodic classification of the elements, and certain outstanding features in the physical properties of some of the elements in these periods, to the fact that at certain stages the electrons which are added to the extra-nuclear configuration, as we pass from element to element in the order of increasing atomic number, go to the enlargement of an inner electron group instead of assisting towards the completion of the only partially filled outermost group. The characteristic X-ray spectra of the elements arise from the creation of a gap in an inner group of electrons and the subsequent readjustment of the atom. The well-known researches of Moseley established the fact that these characteristic X-ray spectra change in an orderly manner, as we pass from element to element down the Periodic Table, the relation between the atomic number and the value of √ ( v /R) for corresponding X-ray lines of different elements being linear [ v denotes the wave-number of the fine, and R, Rydberg’s constant].