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RADIATION EFFECTS ON MATTER (Radiation Dose & Yield (Exposure …
RADIATION EFFECTS
ON MATTER
Energy Transfer
Charged Particles
(Electron, Positrons, Alpha etc.)
The energy of charged particles is absorbed mainly through ionization and atomic excitation.
The average energy, w, for the formation of ion pair in gaseous material is 25 - 40eV.
Since the excitation energies per atom are 5eV, several excited atoms are formed for each ion pair formed.
Uncharged Particles
( Neutrons & Gamma Rays)
The different Ex in these two energy terms is related to the energy loss by electromagnetic radiation (Bremsstrahlung)
Radiation Tracks
energy lost when a high energy charged particle is slowed in a matter gives rise to a trail of ionized and excited molecules along the path of the particle.
A photon imparts a large fraction of its enegy to a single electron, which the ionizes and excites other molecules along its path.
The absorption of any type of ionizing radiation by matter leads to the formation tracks.
Electrons liberated in the ionization process have varies of KE
If the energy of secondary electrons <100eV there is short and ionization and excitations take place close to the primary ionization leading to the formation of small spurs.
Secondary electrons with high KE form tracks of their own branching from the primary tracks.
Radiation Dose & Yield
Exposure
Energy flux of the unperturbed photon radiation when hitting the matter
Unit: Roentgen (R)
IR: Produces ion pairs with total charge per unit mass of 2.58x10^-4 C/kg
Absorbed Dose (D)
Amount of radiation energy absorbed per unit mass
Unit: 1 Grey (Gy) = J/kg = 100 rad
Dose Rate
Absorbed dose per unit time
Unit: Gray per second (Gy/s)
Specific Gamma-ray Dose Rate
Practical measure for estimation of the radiation hazard to people from gamma-emitting radionuclide
Radiation Chemical Yield
Number of molecules of x transformed per 100 MeV absorbed energy.
Unit: mol/J
Large Scale Non-Biological
Applications
The reactive formed on dissociation of molecules by ionizing radiation (radiolysis) can be going further reaction by reduction, oxidation, polymerization, cross-linking, and others.
Radiation Sources
Radioactive Isotopes
Employing Beam Accelerators (EBA)
Dose rate and penetration depth are easily controlled by changing the value of the beam current and acceleration voltage.
Process Criteria
A small amount of chemical change causes a marked change in physical properties.
The radiation induced reaction has a high yield
The radiation has a specific effect or process technical advantages which not easily can be obtained by other methods.
Radiation Induced Synthesis
Synthesis is defined as the production of chemical compounds by reaction from simpler materials.
Ex: sulfoxidation and sulfochlorination by hydrocarbons for detergent production and polymerization of ethene.
Industrial Radiation Processing
Sterilization
Wire & Cable
Shrinkable film & tubing
Curing of surface coating and inks
Potential application
Immbolization or trapping of bioactive material
Radiation treatment