INTERACTION OF RADIATION WITH MATTER – PART 2 FINAL

PHOTOELECTRIC EFFECT

Below 100 kev •It is the emission  of electrons or other free carrier  when electromagnetic  Radiation  like visible light, x rays, y rays hits a material, electrons emits electrons. •Photon transfer all its energy to one of orbital electron of the atom. •Absorption of electron by atom leads to ionization by emission of electron  •Electron acquire kinetic energy of amount equal to that of photon  energy •Electron released in this called photoelectron.

3.1 CHARACTERSTIC RADIATION

•Produced by transition of electron from the outer to inner orbit of the atom (k&m shell)

For transition

•For transition of electron, it is necessary to create vacancy or a hole in inner orbit. •Once vacancy is created in inner shell of atom, electron from the outer shell falls to fill the vacancy. •Potential difference between potential energies of shell in transition is emitted as electromagnetic radiation called characteristic radiation of atom.

•Vacancy in k shell = K x ray •Vacancy in L shell = L x ray •If vacancy  created in k shell- filled by L shell •Difference between two energy eL –eK =  [-63-(-1072)] •Energy emitted as k x ray =1009 ev.

3.2 BREHMSSTRAHLUNG RADIATION

•Radiative collision between electron and nucleus •when electron passing near nucleus suffer a sudden deflection and acceleration by a coloumb force of attraction. By the electron lose their K.E in the form of bremstrahlung x ray.

   also called braking radiation. •Amount of radiation production determined by distance between bombarding electron and nucleus Production increase with accelerating voltage and atomic no. of target material.

4 PAIR PRODUCTION

•Photon energy >1.02 mev passes close to the nucleus of an atom. •It interacts with the nucleus and emission of the positron (e+) and electron is ejected. k/a pair production. •The positron loose its energy after interacting with the electron and liberate annihilated photon of energy 0.51 mev in opposite direction. It is called annihilation process •Reason behind photon move in opposite direction is conserve momentum as they move at 1800

5. NUCLEAR DISINTEGRATION

•Nuclear process, energy of incident photon is more than >7mev •Photon enters to the nucleus and the particle (n+, p+, alpha particle) are emitted.

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