Lecture 34

Health Effects - I

 
Exposure and Absorption
  • There is a subtle difference between exposure to radiation and absorbed dose.
  • Whenever there is a radioactive source emitting radiation, it will irradiate all the material that is exposed to it.
  • However, if the material is transparent to it, then, no energy would be deposited on the material and hence there will not be any radiation damage.
  • As damage due to radiation will be proportional to the energy deposited on the material, it has more importance.
Unit of Exposure

Roentgen
  • Roentgen (denoted by R) is used to quantify the X-ray or γ-ray radiation exposure.
  • It is detected by ionization produced in a gas filled detector.
  • 1 Roentgen is equivalent to generation of 1 ESU of charge in 1 cm3 of air at 0 oC.
  • This is equivalent to 2.58 x 10-4 Coulombs/kg-air or 5.47 x 1010 MeV/kg-air or 87.7 ergs/g-air (Note that 1 electron charge = 1.602 x 10-19 Coulomb and 34 eV is required to create an electron-ion pair).
  • The SI Unit of Exposure is X-unit.
  • 1 X-unit = 1C/kg-air.
  • 1 X-unit = 3881 R.
  • 1 R = 2.58 x 10-4  X-unit.
  • It should be noted that 1R is equivalent to the 87.7 erg/g of absorbed energy in air.