Radiation processing technology - from fundamentals to application

Full text : The radiation technology process is based on the physics and chemistry of radiation interactions in matter and the quantities that are used for monitoring radiation energy depositions. The modifications in a material exposed to ionizing radiation are caused by deposition of energy like thermal or chemical processes. However in any thermal or chemical process the energy transfer is relatively small (from a tiny fraction of an eV to less than 10 eV) comparing with ionizing radiation energy that is imparted in quanta of 10 eV. Taking in account that the binding energies are generally bellow of 12 eV any chemical bond may be broken and/or potential chemical reactions happen during the exposure to ionizing radiation. In the article there is a figure (In IAEA, 1973 Technical Report series 149) from which it can be seen a resume of interaction processes of ionizing photons and electron energy less than 10 MeV. The impact of primary radiation energies (≥ 10 keV ≤ 10MeV) could lead to the degradation and complex interactions with matter which produced a cascade reactions of secondary lower energies. Ionizing radiation with wavelengths less than 10-10 m, such as γ-rays, x-rays and electron beams have a higher energy, causing electron transitions and atom ionization, but the energy imparted in the system is not enough to change the nucleus into a radioactive isotope. The primary radiation energies are produced by electron beams accelerators and electromagnetic radiation (X and gamma rays) produced by machines or by radioisotopes such as cobalt-60 or Cesium-137. The mean energy, dε, imparted by ionizing radiation to an incremental quantity of matter, divided by the mass of that matter, dm, is called the absorbed dose. The definition is given strictly for absorbed dose at a point. In radiation processing, it means the averaged over a finite mass of a given material and is read by a calibrated dosimeter in terms of energy imparted per unit of mass. The unit of absorbed dose is joules per kilogram (J/kg) and is expressed in grays Gy) or multiples of grays (previously rad: 1 Gy = 100 rad). Therefore ionizing radiation is a clean and environmental friendly energy and could be applied to a large range of applications on biology and chemistry fields. The next figure in this article shows some applications and their ranges of absorbed doses usually applied.