The main effect that radiation has on matter is its ability to ionize atoms to convert them into ions, a phenomenon known as ionization, which is very similar to the photoelectric effect. Radioactive particles or electromagnetic waves with sufficient energy collide with the electrons in the atom to expel electrons from the atom. The quantum energy of infrared photons is in the range of 0.001 to 1.7 eV, which is in the range of energies that separate quantum states from molecular vibrations. Infrared is absorbed more strongly than microwaves, but less intensely than visible light.
The result of infrared absorption is the heating of the tissue, since it increases molecular vibrational activity. Infrared radiation penetrates the skin more than visible light and can therefore be used to obtain photographic images of subcutaneous blood vessels. The energy levels of all physical processes at the atomic and molecular levels are quantified and, if there are no quantified energy levels available with spacings that match the quantum energy of the incident radiation, the material will be transparent to that radiation and will pass through it. The ozone layer in the upper atmosphere is important to human health because it absorbs most of the sun's harmful ultraviolet radiation before it reaches the surface.
In addition to ionizing radiation, chemical reactions and thermal effects can also cause radical formation. The higher frequencies of ultraviolet radiation are ionizing radiation and can produce harmful physiological effects that range from sunburn to skin cancer. The OH radicals were obtained by removing an α-hydrogen from the isopropanol molecule by UV irradiation. The key is its interaction with matter or, more specifically, whether the energy of the photon is adequate to excite a transition of a charged particle.
Different parts of the electromagnetic spectrum have very different effects on interaction with matter. The radiation weighting factor (wR) is a number that represents the value of the relative biological efficacy (RBE) of radiation. In other words, the more subatomic particles there are in a material (the higher the Z number), the greater the probability that interactions will occur. Similarly, the more material a photon must pass through, the more likely it is to be found.
Among the methods of forming radicals in the structure of matter, ionizing radiation plays an important role. However, it has been shown that the glass needed for UV radiation is also suitable for electronic resonance studies, since small defects that severely disperse UV wavelengths have no effect on microwave radiation. The separation of chemical bonds with radiation is one of the most common and direct methods that can be used to produce molecular fragments and free radicals. It must be assumed that the radiation of interest completely releases the chemical bond and leaves behind two one-electron molecules containing an unpaired electron.
The easiest way to do this is to place a protective shield around the radioactive source; alpha particles can be stopped by a layer as thick as a sheet of paper, beta radiation cannot penetrate more than a few centimeters of aluminum, while gamma rays are almost impossible to stop. Electron spin resonance (paramagnetic) spectra of the radicals resulting from high-energy irradiation function at high signal-to-noise ratios. Understanding how radiation interacts with matter allows us to protect ourselves from harmful effects.
