MRD441: Radiation Biology & Safety PDF

MRD441: RADIATION BIOLOGY & SAFETY  COURSE OBJECTIVE Upon completion of this lecture, the student should be able to: 1. Describe the basic structure of an atom 2. List the types of radiation. 3. Describe types of radiation. 4. Differentiate types of radiation.  Describe the radiation eff...

MRD441: RADIATION BIOLOGY & SAFETY  COURSE OBJECTIVE Upon completion of this lecture, the student should be able to: 1. Describe the basic structure of an atom 2. List the types of radiation. 3. Describe types of radiation. 4. Differentiate types of radiation.  Describe the radiation effects on prenatal and postnatal life Describe the stochastic and deterministic effects of low level radiation over and extended period of time Explain radiographic equipment specifications for radiation protection purposes Explain methods of radiation detection and its measurement INTRODUCTION  Atomic Structure 1870 - Mendeleef 1913 - Danish physicist - Niels Bohr Central positive Elements arranged nucleus with according to their surrounding in the orbits negatively atomic weight charged electrons Atomic Structure (cont.) In Nucleus ▪ Neutrons (neutral) and Protons (+) Elementary ▪ Electrons (-)  Atomic Structure (cont.) Atomic Number (Z) Neutral atom: number of electrons is equal to protons A where: Z X ▪ X - chemical symbol of element ▪ A - mass number (= number of protons + number of neutrons) ▪ Z - atomic number (= number of protons)  Atomic Structure (cont.) Isotopes and Nuclides Isotopes ▪ Atoms of the same atomic number but different mass number. ▪ Equal number of protons but different number of neutrons. ▪ E.g. 1H, 2H, 3H. o Isotopes refer to the same element. o Isotopes of any element may also be called nuclides.  WHAT IS RADIATION Propagation of energy through space or matter Man made o Nuclear reactors o Artificially produced radioactive materials Natural background o Cosmic rays o Earth sources  WHY RADIATION PROTECTION IS SO IMPORTANT?  Biological Response to Ionizing Radiation X-ray interactions with matter (human tissue) can cause biological changes. Technologists must understand cellular biology and how radiation interacts with cells in order to protect oneself and the patient. THE EARLY YEARS  HISTORY OF RADIATION Early radiation workers Radium miners Luminous dial painters Atomic warfare Power plant accidents Types of Ionizing Radiation cosmic X-rays  4He 2 neutron -rays  Electron - + (negatron) (positron)  Four Primary Types of Ionizing Radiation Alpha particles Beta particles Gamma rays (or photons) X-Rays (or photons) Neutrons  Types of Ionizing Radiation (cont.) Alpha Particle Helium nucleus: 2 protons and 2 neutrons tightly bound together. Emitted from naturally occurring radio nuclides such as uranium and thorium. Lose energy by collisions with atomic electrons - cause ionizations to occur. Directly ionizing particles - cause ionization of an atom without any intermediate interaction taking place.  Types of Ionizing Radiation (cont.) Alpha Particle Cause large specific ionization (number of ion pairs formed per unit energy) because of their double positive charge and large mass. Lose their energy in short distance hence range in media is short (less of external hazard but present an internal hazard). Alpha decay Alpha energy spectrum  Types of Ionizing Radiation (cont.) Beta Particles High speed electrons emitted by a radionuclide. Either be positive (positron) or negative (electrons). Not emitted with discrete energies but show a continuous energy spectrum (unlike alphas). Lose energy more frequently through ionization and excitation.  Types of Ionizing Radiation (cont.) Beta Particles Directly ionizing particles - cause ionization of an atom without any intermediate interaction taking place. For high speed electron (more than 1 MeV) more energy may be lost in the form of X- rays due to interaction with the nuclear field in dense material (bremsstrahlung).  Types of Ionizing Radiation (cont.) Beta Particles Produce less ionization per unit length than alpha particles because of its smaller mass and charge. Have greater range than alpha hence, depending on its energy constitute an external hazard. Not as great an internal hazard as alpha particles. Beta decay  Types of Ionizing Radiation (cont.) Neutrons No electrical charge Mass slightly higher that proton Nucleons = protons + neutrons Important in atomic nucleus as they bind with protons via strong force  Types of Ionizing Radiation (cont.) X- and Gamma-Rays Electromagnetic waves or photons. Ionization produced is almost all secondary. Most concern as potential external hazards. Great range in air and other media. High Z shielding material is needed to prevent or minimize the intensity of radiation hazard.  Gamma-ray X-ray Emitted by radioactive Produce when highly isotopes accelerated electrons are bombard a target Produce intranuclearly Produce extranuclearly  Radioactive Atom Ionizing Radiation alpha particle X-ray beta particle gamma ray  Wave-particle duality - Photons EM energy displays particle-like behavior, and sometimes it acts like a wave; it all depends on what sort of experiment you're doing. This is known as wave/particle duality  Characteristics of Radiation Visible light Light interacting with matter oReflected oTransmitted oAttenuated oAbsorbed  Characteristics of Radiation X-rays X-rays interacting with matter oScatter oTransmitted oAttenuated oAbsorbed oRadiopaque oRadiolucent  Patient Interactions **Photoelectric** Classic Coherent Scatter **Compton Scattering** Pair Production Photodisintegration Interaction in The body begin at the atomic level Atoms Molecules Cells Tissues Organ structures X-ray photons can change cells  atoms in materials through which they pass, and can therefore he hazardous to living tissue. 1913