Fathi

Types of Ionizing Radiation Absorption of energy from radiation in biological material may lead to excitation or to ionization. Excitation – electron from atom or molecule raised to a higher energy level but not ejected. Ionization – ejection of one or more electrons. IONIZING RADIATION

Electromagnetic Radiation X-rays or gamma-rays – do not differ in nature or properties but are produced in different ways. X-rays are produced extranuclearly (from orbital electrons) Gamma-rays are produced intranuclearly (from decay of an unstable nucleus – radioactive element)

X-rays are waves of electrical and magnetic energy Wave moves with velocity (c). [3x1010 cm/s] Distance between peaks is wavelength ( ) # waves passing a fixed point is frequency ( ) =c

X-rays can be thought of as photons, or packets of energy Each packet has energy = h h=Plank’s Constant

= frequency

Photon Energy (in kiloelectron volts) keV is the energy possessed by an electron that has been acelerated through 1000 volts. Photon energy in excess of 124 eV is considered ionizing

Absorption of X-rays Directly Ionizing (Particulate Radiations – Electrons, Protons, alpha-particles, Neutrons Indirectly Ionizing (X-rays and gamma-rays) The way photons are absorbed depends on the energy of the photon and the chemical composition of the absorbing material.