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Third lecture. Interactions of radiation with matter. (1)-Interaction of with matter:- i-T he particle follows a straight, short path in the material it penetrates. ii-It causes very dense ionization & excitation events along the track.
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Interactions of radiation with matter (1)-Interaction of with matter:- i-The particle follows a straight, short path in the material it penetrates. ii-It causes very dense ionization & excitation events along the track. iii-the most ranges are less than 5-6 cm in air.
Interactions of radiation with matter (2)-Interaction of with matter:- i-The particle scatters frequently, causing what is often described as a drunken man’s path. ii-the range of is considerably greater than an . iii-ionization & excitation events along the path are much less than that due to
Interactions of radiation with matter (3)-Interaction of with matter:- • It depends on the photon energy & the atomic number of the material. • Photon can be absorbed by photoelectric effect; it can be scattered by Compton scattering; and it can be converted to particles of mass by pair production.
(3)-Interaction of with matter:- • photoelectric effect: • The incoming photon is absorbed to a k orbital electron. • Then the electron is ejected from the atom. • This electron causes further ionization. • X-ray is often emitted when the vacancy is filled.
(3)-Interaction of with matter:- Compton scattering: • Is scattering of or x-ray by an outermost electron in an atom. • The photon changes direction, looses partial energy. • The electron is kicked out of the atom. • The electron & the scattered photon cause further ionization.
(3)-Interaction of with matter:- pair production: i-It is possible when the incoming photon energy is above 1.02 MeV. ii-The photon disappeared in the field of the nucleus & replaced by an electron-positron pair. iii-The positron is a positively charged particle with a mass of normal electron. iv-When it reaches its final track, it combines with a normal negative electron in a process known as annihilation.