Non-ionizing radiation.pptx

Non-ionizing radiation

1. Non-ionizing radiation Dr. Hiba ZBIB 2015-2016 1

2. Non-Ionizing Vs Ionizing radiation Radiation that has enough energy to move atoms to vibrate, but not enough energy to remove electrons. The process by which a neutral atom acquires a positive or a negative charge is know as Ionization. Removal of an orbital electron leaves the atom positively charged, resulting in an ion pair. Molecule with a net positive charge. Free electron with a negative charge. 2

3. Nonionizing radiation (NIR) The classification of radiation as ionizing is essentially a statement that it has enough energy to eject an electron. This is crucial distinction, since ionizing radiation can produce a number of physiological effects, such mutation or cancer , which non-ionizing radiation cannot directly produce at any intensity. 3

4. Non-ionizing radiation Radiation in the visible or longer wavelength range does not have sufficient energy to ionize an atom, so we classify it as non-ionizing radiation . The threshold for ionization occurs somewhere in the ultraviolet range , with the specific threshold depending upon the type of atom or molecule. 4

5. Interaction of radiation with matter If there are no available quantized energy levels matching the quantum energy of the incident radiation, then the material will be transparent to that radiation Wavelength 5

6. Interaction of radiation with matter The different parts of the electromagnetic spectrum have very different effects upon interaction with matter. Low frequency radio waves : the human body is quite transparent. Microwaves and infrared to visible light : you absorb more and more strongly. Ultraviolet range : all the UV from the sun is absorbed in a thin outer layer of your skin. 6

7. Interaction of radiation with matter X-ray: you become transparent again. You then absorb only a small fraction of the radiation, but that absorption involves the more violent ionization events. Each portion of the electromagnetic spectrum has quantum energies  appropriate for the excitation of certain types of physical processes. If electromagnetic energy is absorbed, but cannot eject electrons from the atoms of the material, then it is classified as non-ionizing radiation , and will typically just heat the material . 7

8. Molecular absorption processes Electronic transitions UV and visible wavelengths Molecular vibrations Thermal infrared wavelengths Molecular rotations Microwave and far-IR wavelengths Each of these processes is quantized Increasing energy 8

9. Microwave interactions Quantum energy of microwave photons (0.00001-0.001 eV ) matches the ranges of energies separating quantum states of molecular rotations. Note that rotational motion of molecules is quantized , like electronic and vibrational transitions. Absorption of microwave radiation causes heating due to increased molecular rotational activity. Since the quantum energies are a million times lower than those of x-rays, they cannot produce ionization. 9

10. Infrared Interactions The term "infrared" refers to a broad range of frequencies, beginning at the top end of the microwaves and extending up to the low frequency (red) end of the visible spectrum. The range adjacent to the visible spectrum is called the "near infrared" and the longer wavelength part is called "far infrared". 10

11. Infrared Interactions Infrared is absorbed more strongly than microwaves, but less strongly than visible light. The result of infrared absorption is heating of the tissue since it increases molecular vibrational activity. 11

12. Infrared (IR) interactions Quantum energy of IR photons (0.001-1.7 eV ) matches the ranges of energies separating quantum states of molecular vibrations. Vibrations arise as molecular bonds are not rigid but behave like springs. A single molecule can vibrate in various ways; each of these different motions is called a vibration "mode".  12

13. Visible Light Interactions The primary mechanism for the absorption of  visible light photons is the elevation of electrons to higher energy levels. There are many available states, so visible light is absorbed strongly. 13

14. Ultraviolet interactions Near UV radiation (just shorter than visible wavelengths) is absorbed very strongly in the surface layer of the skin by electron transitions. At higher energies, ionization energies for many molecules are reached and the more dangerous photoionization processes occur. Sunburn is primarily an effect of UV radiation, and ionization produces the risk of skin cancer.

15. Ultraviolet Interactions The ozone layer is important for human health because it absorbs most of the harmful ultraviolet radiation from the sun before it reaches the surface. The higher frequencies in the ultraviolet are  ionizing radiation  and can produce harmful physiological effects ranging from sunburn to skin cancer. 15

16. UV LIGHT Light with wavelengths between 100 nm and 400 nm. The UV spectrum is divided into three regions: UVA, 320–400 nm; UVB, 280–320 nm; and UVC, 100–280 nm. 16

17. Sources of UV radiation The sun is the largest source of UV radiation; the sunlight that reaches the earth’s surface consists mainly of UVA radiation, with a smaller component of UVB. All of the UVC is filtered by the ozone layer, and thus no UVC reaches the earth’s surface. Man-made sources of UV radiation: black light lamps 17

18. X-ray interactions (IR) Quantum energies of x-ray photons are too high to be absorbed by electronic transitions in most atoms - only possible result is complete removal of an electron from an atom Hence all x-rays are ionizing radiation If all the x-ray energy is given to an electron, it is called photoionization If part of the energy is given to an electron and the remainder to a lower energy photon, it is called Compton scattering

19. Absorption of radiation by molecules Atoms and molecules can absorb electromagnetic radiation, but only at certain energies (wavelengths). The three groups of lines correspond to different electronic configurations. Certain energies in the visible and UV regions of the spectrum can cause electrons to be excited into higher energy orbitals ; 19

20. Absorption of radiation by molecules Photons in the infrared region of the spectrum can excite  vibrations  in molecules. There are many possible vibrational levels within each electronic state. Transitions between the vibrational levels are indicated by the vertical arrows on the left side of the diagram. 20