the hole created by L and M shell is ocuppied by
Answers
When the speed of bombarding electrons are extremely high (about One-tenth of the velocity of light) some of these electrons may penetrate deep into the atoms of the target and collide with tightly bound electrons of the inner shells of the atoms. It may be possible that m collision the bombarding electron transfers all its energy to an electron bound in one of the inner shells, such as K or L, of the target atom, and the same bound electron is ejected from its orbit. The removal of an electron from the inner shell creates a vacancy (or hole) in the shell or in its low energy level. TO fill this low energy vacancy, an electron from a higher energy level jumps in, and the excess energy is radiated in the form of X-ray photons. Thus, the energy of X-ray photons is determined by the difference between the energies of two levels. The X-rays emitted in this way are called the characteristic X-rays because their frequencies are the characteristic of the atoms of the material of the target from which they are ejected. Suppose high speed bombarding electron knock off one electron from the K-shell, as shown in Fig. (a), so that a vacancy (or hole) is created in the shell. The electron from nearby L-shell jumps to occupy the hole in the K-shell [(Fig. (b)]thereby emitting X-ray photon of Energy hvkahvka and is given by
hvka=EK−KLhvka=EK-KL
This corresponds to KaKa line of K-series or called KaKa X-ray.
If however, the vacancy in K-shell is filled up by an electron jump from the M-shell, or N-shell, the x-rays emitted would be still more energetic (or still of higher frequency) and are called KβKβ and KrKr x-rays with energies
hvkβ=EK−KMhvkβ=EK-KM
hvkr=EK−KNhvkr=EK-KN
and so on.
Such x-rays arising from millions of atoms produced K-lines as shown in figure below. The holes so created in the L-and M-shells are filled by transitions of electrons from higher states, producing more X-rays. The process is continued until the vacancy reaches the outermost shell series is always accompanied by the emission of L-, M-, N-... series.
Suppose the high speed bombarding electrons carry a lesser amount of energy, which is sufficient to knock off an electron from the L-shell. In this case an electron from outer-shells (e.g. M or N or...) jumps to the L-shell to fill the vacancy and excess energy is emitted as X-ray photons. These X-rays are less energetic than that of K-series and are called to from L-series of X-rays emission spectrum. L-series of characteristic X-ray spectrum consists of LdLβLγLdLβLγ ... lines etc. lines caused by the jumping of electrons to fill the vacancy in L-shell from M, N, 0,... etc. shell respectively with energies