Physics of Atom Lecture No. 3 PDF

Al-Salam University College Department of Radiology Techniques Physics of atom Lecture No:3 Prepared by : Assist.Lect. Safa Sami Dr. saad Thabet Classification of Radiation : -Radiation: It is...

Al-Salam University College Department of Radiology Techniques Physics of atom Lecture No:3 Prepared by : Assist.Lect. Safa Sami Dr. saad Thabet Classification of Radiation : -Radiation: It is defining as the transfer of energy or the emission of energy as either waves (electromagnetic radiation) or particles. It comes from a source and travels through some material or through space. It is produced by radioactive decay, nuclear fission and nuclear fusion, chemical reactions, hot objects. Radiation occurs when energy is emitted by a source, then travels through a medium, such as air, until it is absorbed by matter. Radiation can separate into two categories according to it energy and danger; ionizing and non- ionizing. 1) Ionizing radiations: Ionizing radiation is a special type of radiation (in the form of either particles or waves) that has enough energy to remove tightly bound electrons out of their orbits around atoms, thus creating ions. In other words, ionizing radiation is any kind of radiation capable of removing an orbital electron from an atom with which it interacts, the atom is said to be ionized. This process is called ionization. Ionizing radiation includes the radiation that comes from both natural and manmade radioactive materials. Examples of this kind of radiation of interest for the purpose of this chapter are gamma (γ) and x-rays. Gamma radiation consists of photons that originate from within the nucleus, and X-ray radiation consists of photons that originate from outside the nucleus, and are typically lower in energy than gamma radiation. We take advantage of its properties in diagnostic imaging, to kill cancer cells, and in many manufacturing processes. Ionization is the process by which a stable atom or a molecule loses or gains an electron(s). In the human body, these effects may lead to changes in the structure or behavior of cells. Therefore, ionizing radiation has sufficient energy to be able to displace an electron from its orbit around an atom and, conversely, non-ionizing radiation does not have sufficient energy to displace electrons. Ionizing radiation can occur in one of two forms: particulate or electromagnetic. ionizing radiation: It is the radiations that excite and ionize atoms of matter with which they interact, since the energy need to escape a valence electron from atom is (4-25 eV). That mean it is have a high energy to interact with human cells and ionizing them. It includes: a) Particulate Ionizing radiation. b) Electromagnetic Ionizing radiation (photon radiation) a) Particulate Ionizing radiation: Particle radiation consists of a stream of charged or neutral particles, both charged ions and subatomic elementary particles. This includes solar wind, cosmic radiation, and neutron flux in nuclear reactors. Charged particles: it's directly ionized matter, such as; 1) Fast electron (beta, positron). 2) Heavy Charged Particle: a) Proton-the hydrogen nucleus. b) Deuteron-the deuterium nucleus, consisting of a proton and neutron. c) Triton-a proton and two neutrons, tritium nucleus. d) Alpha - helium nucleus, (two protons and two neutrons). e) Nuclear fragments Uncharged particles: Its indirect ionizes matter such as neutron.  Uncharged particles: Its indirect ionizes matter such as neutron. b) Electromagnetic Ionizing radiation: In general, electromagnetic radiation consists of emissions of electromagnetic waves, the properties of which depend on the wavelength. Ionizing radiation has more energy than nonionizing radiation such that it can cause chemical changes by interacting with an atom to remove tightly bound electrons from the orbit of the atom, causing the atom to become charged or ionized. The types of ionizing electromagnetic radiation are categorized according to their wavelength. Ionizing electromagnetic radiation includes U.V., gamma and X- ray. All forms of electromagnetic radiation (which includes radio waves, light, cosmic rays, etc.) moves through empty space with the same velocity at the speed of 299,792 km per second (very close to 3×108 m.s -1) and not significantly less in air. They include 2) Non-Ionizing Radiation: is the radiation that has enough energy to move atoms in a molecule around or cause them to vibrate, but not enough to remove electrons. That mean it does not possess enough energy to produce ions (that do not have a sufficient energy to remove electrons from atoms, and hence can't interact with matters or ionizing them). Non-ionizing radiation consists of parts of the electromagnetic- spectrum (Figure 2), which includes radio waves, microwaves, infra-red, visible and ultraviolet light, together with sound and ultrasound. Cellular telephones, television stations, FM and AM radio, and cordless phones use non-ionizing radiation.