Modern Physics> X-rays...

Write about characteristic & continuous x rays

Zubair Younis Ringshawl , 15 Years ago

Grade 12

3 Answers

Askiitians Expert Bharath-IITD

Last Activity: 14 Years ago

Dear Zubair,

In an X ray setup we have a source(cathode) of electrons which are acclerated by electric field and a target anode.

The electrons achieve high velocities due to electric field. Now these elctrons undergo deceleration when they bombard on the target. This deceleration occurs continuosly after the elctron travells deep into the target and corresponnding energy is emitted as X ray spectrum. All velocity values are possible for these elctrons starting from zero to the maximum possible velocity obtained by equating the kinetic energy and product of voltage & charge of electron which is nothing but the energy provided by electric field for the elctron. This is for this reason that the spectrum obtained is continuous and is same for all materials.

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Adapa Bharath

Askiitians Expert Bharath-IITD

Last Activity: 14 Years ago

Dear Zubair,

Sorry that i forgot to mention about the characteristic x rays in the previous reply.

As we already known how continuous spectrum is obtained, the charecteristic x rays are obtained by a special process.

In this process the elctrons effect the target at atomic level. When an elctron hits an atom it pulls out its elcrtron in the inner shell or orbit thus leaving it empty.

But the electrons in the other orbits will jump to that orbit thus projducing a vaccancy again and this process continues untill the last orbit electron jumps to that of before it.

Thus we would get spectrum which is discontinuous becaude the energy difference between the adjacent orbits in an atom are not continuous but rather some fixed and discontinous.

The spectrum thus obtained is callled charateristic xrays because every element has its own energy value thus not same for all elements, so the same characteristic.

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Adapa Bharath

gaurav

Last Activity: 9 Years ago

Sometimes a high velocity electron passes close to the nucleus of an atom within the target of the X-ray tube.During the process the electron experiences a strong Coulomb force of attraction due to the nucleus and is suddenly slowed down, at the same time suffering a deflection in its path.
During its retardation the electron emits a pulse of e.m. radiation of energy hf. Since the electron suffers all sorts of collisions the retardation suffered is also different. Hence the energy of the emitted X-rays also vary . Hence the X-ray spectra shows all possible wavelengths within a certain range . This gives rise to a continuous spectra (a continuous curve).

2) In some collisions an electron coming with high velocity penetrate through the outer shells of the electrons and strike against an electron in the inner shell, and knockout an electron from the inner shell of the atom . The incident and the dislodged electrons both escape from the atom causing a vacancy in the innermost K shell. An electron from the outer shell (say L shell) in higher energy state jump to the K shell to fill the vacancy . This gives rise to an X-ray photon of energy hf. This causes a vacancy in the L shell , which is again filled up by another electron jumping from one of the outer shells along with the emission of another X-ray photon of different energy.. This process continues till the outer-most shell is reached, thus resulting in the emission of a series of characteristic X- ray photons. This gives rise to sharp lines or peaks superimposed on the continuous line.