2 Physical principles of radiat.pdf

Stay Home-Stay Safe Introduction to Radiography & Medical Imaging Lecture 2: Physical principles of radiation science Introduction to Radiography & Medical Imaging Slide 1 fchs.ac.ae Radiation fchs.ac.ae Definition of Radiation “Radiation is an energy in the form of electro-magnetic waves or particu...

Stay Home-Stay Safe Introduction to Radiography & Medical Imaging Lecture 2: Physical principles of radiation science Introduction to Radiography & Medical Imaging Slide 1 fchs.ac.ae Radiation fchs.ac.ae Definition of Radiation “Radiation is an energy in the form of electro-magnetic waves or particulate matter, traveling in the air.” fchs.ac.ae Radioactivity: Elements & Atoms Atoms are composed of smaller particles referred to as: – Protons – Neutrons – Electrons fchs.ac.ae Basic Model of a Neutral Atom. Electrons (-) orbiting nucleus of protons (+) and neutrons. Same number of electrons as protons; net charge = 0. Atomic number (number of protons) determines element. Mass number (protons + neutrons) fchs.ac.ae fchs.ac.ae Radioactivity If a nucleus is unstable for any reason, it will emit and absorb particles. There are many types of radiation and they are all pertinent to everyday life and health as well as available nuclear physical applications. fchs.ac.ae Ionization Ionizing radiation is produced by unstable atoms. Unstable atoms differ from stable atoms because they have an excess of energy or mass or both. Unstable atoms are said to be radioactive. In order to reach stability, these atoms give off, or emit, the excess energy or mass. These emissions are called radiation. fchs.ac.ae Types or Products of Ionizing Radiation  neutron  or X-ray fchs.ac.ae Radioactive Atom Ionizing Radiation alpha particle X-ray beta particle gamma ray fchs.ac.ae The electro-magnetic waves vary in their length and frequency along a very wide spectrum. fchs.ac.ae Forms of Electromagnetic Radiation fchs.ac.ae fchs.ac.ae Types of Radiation Radiation is classified into: – Ionizing radiation – Non-ionizing radiation fchs.ac.ae Ionizing Versus Non-ionizing Radiation Ionizing Radiation – Higher energy electromagnetic waves (gamma) or heavy particles (beta and alpha). – High enough energy to pull electron from orbit. Non-ionizing Radiation – Lower energy electromagnetic waves. – Not enough energy to pull electron from orbit, but can excite the electron. fchs.ac.ae Ionizing Radiation X-ray radiation contains more energy than ultraviolet, infrared, radio waves, microwaves or visible light. X-ray radiation has sufficient energy (>30 eV) to cause ionizations. An ionization is a process whereby the radiation removes an outer shell electron from an atom fchs.ac.ae Non-ionizing radiation does not contain sufficient energy (30 eV) to cause ionizations fchs.ac.ae Ionizing Radiation Definition: “ It is a type of radiation that is able to disrupt atoms and molecules on which they pass through, giving rise to ions and free radicals”. fchs.ac.ae Another Definition Ionizing radiation A radiation is said to be ionizing when it has enough energy to eject one or more electrons from the atoms or molecules in the irradiated medium. This is the case of a and b radiations, as well as of electromagnetic radiations such as gamma radiations, X-rays and some ultra-violet rays. Visible or infrared light are not, nor are microwaves or radio waves. fchs.ac.ae Primary Types of Ionizing Radiation Alpha particles Beta particles Gamma rays (or photons) X-Rays (or photons) Neutrons fchs.ac.ae Types and Characteristics of Ionizing Radiation Alpha Particles: 2 neutrons and 2 protons They travel short distances, have large mass Only a hazard when inhaled to realse stable radioactive fchs.ac.ae Beta Particles Beta Particles: Electrons or positrons having small mass and variable energy. Electrons form when a neutron transforms into a proton and an electron or: poistrons when proton transform to nuetrons and poistrons fchs.ac.ae Gamma Rays Gamma Rays (or photons): Result when the nucleus releases energy, usually after an alpha, beta or positron transition fchs.ac.ae X-Rays X-Rays: Occur whenever an inner shell orbital electron is removed and rearrangement of the atomic electrons results with the release of the elements characteristic X-Ray energy fchs.ac.ae X- and Gamma Rays: X-rays are photons (Electromagnetic radiations) emitted from electron orbits. Gamma rays are photons emitted from the nucleus, often as part of radioactive decay. Gamma rays typically have higher energy (Mev's) than X-rays (KeV's), but both are unlimited. fchs.ac.ae Neutrons Neutrons: Have the same mass as protons but are uncharged fchs.ac.ae X-RAY PRODUCTION fchs.ac.ae X-RAY TUBE The X-ray tube is an evacuated glass cylinder containing cathode and anode. The cathode is heated and emits electrons. The high voltage between cathode and anode accelerates the electrons towards the anode. The high energy electrons collide with the anode and interact with the anode material by creating the typical radiation of the anode element ( W: tungsten) fchs.ac.ae fchs.ac.ae X-ray Machine Parameters ‫كم مقدار االشعه طالعه‬ The quantity of electron flow (current) in the X-ray tube is described in units of milliamperes (mA). The rate of X-ray production is directly proportional to the X-ray tube current. The voltage (kVp) primarily determines the maximum Xray energy (quality) produced but also influences the number of X-rays produced. Total number of X-rays produced at a set kVp depends directly on the product of the mA and exposure time and is typically described in terms of mAs. fchs.ac.ae X-Ray X-ray is one of the main diagnostic tools in medicine and is a form of electro-magnetic waves. They are shorter in wavelength than UV rays, longer in wavelength than gamma rays. fchs.ac.ae 1- Travel in straight lines. 2- Have a high penetrating power. 3- Photographic film is blackened by X-rays. 4- Not deflected by electric or magnetic fields. 5- Wavelength range of 0.01 to 10 nanometers. fchs.ac.ae fchs.ac.ae X-rays are produced when rapidly moving electrons that have been accelerated through a potential difference within an evacuated glass tube of order 1 kV to 1 MV strikes a metal target. fchs.ac.ae fchs.ac.ae X-Ray tube components 1- Glass envelope 2- Cathode 3- Anode 4- Protective housing fchs.ac.ae Anode parts 1- Router 2- Stator windings 3- Rotated disc fchs.ac.ae Cathode parts 1- Filament 2- Focusing cup fchs.ac.ae Steps of production of X-rays: 1- The source of electrons is the filament , heated by electric current 2- A high potential energy is applied, anode becomes strongly positive, cathode becomes strongly negative fchs.ac.ae 3- The electrons are forced to form a narrowing beam ( focusing cup) to the target. 4- Electrons are attracted towards the target and then the x-rays are produced when they hit the target. fchs.ac.ae The energy of the x-rays is dependent on the kinetic energy of the electrons. The kinetic energy of the electrons is converted into electromagnetic energy( x-ray) & heat in ratio of 1:99 correspondingly. (99% heat &1% x-ray) fchs.ac.ae SEE YOU NEXT CLASS Slide 42 fchs.ac.ae