Ionizing and Non-Ionizing Radiation

Radiation HazardsDamage

1. The production of lesions in solute molecules directly (e.g. by rupturing of covalent bonds);

2. Indirect action between molecules and the free radicals e.g. (a hydroxyl free radical):

H2O + radiation à H2O+ + eH2O+ + decomposes -> H+ + OH-

Linear energy transfer: the sum of the energy deposited in tissue per unit path length (e.g., J/cm)e.g. electrons produce ionization over a distance that is large compared with cellular dimensions (low-LET); alpha particle – travel shorter distances and thus are much more closely spaced energy deposition (high-LET); cellular overkill

Radiation HazardsFreeradicals:anatom,molecule,orionthathasunpairedvalenceelectronsoranopenelectronshell

deterministiceffects increasesasthedoseofexposureincreases.Becauseofanidentifiablethresholdlevel,andIrreversible-hasathresholdofdose-severityoftheeffectisdose-related

Stochasticeffectsbychanceprobabilityofaneffectincreaseswithdose-nodosethreshold-severityoftheeffectisnotdoserelatedAchangeincellscanleadto:- Cancermaineffect- GeneticeffectsCanhappenindependentofdose,butprobabilityincreasewithdose

Radiation HazardsStochastic (Genetic, Hereditable) Effects of Radiation

Stochastic effects appear in the future generations of the exposed person as a result of radiation damage to the reproductive cells

most vulnerable to radiological damage is DNA

ThecellismostsensitivetoirradiationdamageattheMitosis(M)phase

deceaseswithage

Radiation DosimetryAbsorbed Dose

• The effect of ionizing radiation is correlated with the energy deposited as ionization (excitation) of atoms;

• The absorbed dose equals the energy deposited per unit mass of the material

1 Gy (Gray) = 1 J/kgOld (CGS) unit (rad): 1Gy = 100 rad;

• It depends on radiation and the absorbing material, i.e, no proper for health measurement effects on human.

• 1 Gy alpha radiation is more hazerdous than 1 Gy of photon radiation.

• At low energiesAbsorbed dose =Gy Ionization energy + Gy for Kerma (kinetic energy released to matter)• At high energiesKerma > Absorbed dose du to energy escaping in the form of Bremsstralung

Radiation HazardsDeterministic Effects of Radiation

Gonads sexual glands, Intestinal epithelial cells (Colon) , lung ….. The most sensitive cell to radiation

Radiation Dosimetry

Dosimeters

Lithium fluoride thermoluminescence dosimeters;

The photographic effect in silver bromide (film badges), photochemical process;

Photoconductivity in silicon diodes used in direct reading electronic personal dosimeters;

Assumethatthesamedoseofradiationisgiven,thenthehighestcarcinogenic(potentialtocausecancer)effectisexpectedfrom

protonsα particleradiationβ radiation (electrons/positron)X-rayγ rayproductionIonizationNeutrons50keV

Directactionofradiationisthedominantprocessfor:

X-raysα radiationScatteredphotonsγ- raysPhotoelectrons

Themostsensitivecelltoradiationisthe:

RedbloodCellNeuronFibroblastBonemarrowcellsdermalcellsMusclecells

Radiation HazardsDose and Units