Lecture 6: Radiochemistry PDF

‫ﺑﺳم ﷲ اﻟرﺣﻣن اﻟرﺣﯾم‬ ‫‪1‬‬ Radiochemistry 2 3  What is Radiation? Invisible energy waves or particles What is Radioactivity? The radioactivity is the property of some atoms to spontaneously give off energy as particles or rays. The atoms that mak...

‫ﺑﺳم ﷲ اﻟرﺣﻣن اﻟرﺣﯾم‬ ‫‪1‬‬ Radiochemistry 2 3  What is Radiation? Invisible energy waves or particles What is Radioactivity? The radioactivity is the property of some atoms to spontaneously give off energy as particles or rays. The atoms that make up the radioactive materials are the source of radiation. 4  Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons.  Radioactivity it is the emission of particles and energy by isotope.  Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles (ionizing radiation). 5  Nuclear radiation the nuclei of unstable isotopes undergo spontaneous nuclear reaction that causes liberation of new particles and energy.  The radiation emitted can be one of three types, called alpha, beta, or gamma radiation 6 1. α (alpha) radiation- The emission of an alpha particle (which contains 2 protons and 2 neutrons) from an atomic nucleus. When this occurs, the atom’s atomic mass will decrease by 4 units and atomic No. will decrease by 2 particles. 7  Alpha Particles  Two neutrons and two protons  Charge of +2  Emitted from nucleus of radioactive atoms  Transfer energy in very short distances (10 cm in air)  Shielded by paper or layer of skin  Primary hazard from internal exposure  Alpha emitters can accumulate in tissue (bone, kidney, liver, lung, spleen) causing local damage 8  Alpha Radiation Alpha particles contain two protons and two neutrons 9 2. β (beta) radiation- the transmutation of a neutron into an electron and a proton. After this happens, the electron is emitted from the nucleus into the electron cloud. 10  Beta Particles  Small electrically charged particles  Similar to electrons  Charge of -1  Ejected from nuclei of radioactive atoms  Emitted with various kinetic energies  Shielded by wood, body penetration 0.2 to 1.3 cm depending on energy  Can cause skin burns or be an internal hazard of ingested 11  Beta-minus Radiation Beta-minus particles are electrons 12 3. ɣ (gama)radiation-it consists of photons with a frequency of greater than 1019 Hz. It is much like X-rays, and can pass completely through the human body. Thus gamma rays emitted from outside of the body may cause ionization, and possible health effects, in any organ in the body. 13  Gamma - Rays  Electromagnetic photons or radiation (identical to x-rays except for source)  Emitted from nucleus of radioactive atoms – spontaneous emission  Emitted with kinetic energy related to radioactive source  Highly penetrating – extensive shielding required  Serious external radiation hazard 14  Gamma Radiation Gamma rays are a form of electro- magnetic radiation 15 Beta-plus Radiation + particles are positrons 16  X-rays have smaller wavelengths and energy higher than ultraviolet waves. X- ray light tends to act more like a particle than a wave. X-rays have a wavelength in the range of 0.01 to 10 nanometer, and energies in the range 120 eV to 120 keV. 17  X-ray can form ions in matter by knocking electrons off the atoms and molecules in its path creating ions, that’s why it is called ionization radiation. The Electromagnetic Spectrum 18  X-rays  Overlap with gamma-rays  Electromagnetic photons or radiation  Produced from orbiting electrons or free electrons – usually machine produced  Produced when electrons strike a target material inside x-ray tube  Emitted with various energies & wavelengths  Highly penetrating – extensive shielding required  External radiation hazard  Discovered in 1895 by Roentgen 19  Penetrating power α has a high mass, It is stopped by a few centimetres of air β has a small mass, It is stopped by a few millimetres of aluminium Ɣ has zero mass, It is stopped by thick lead or concrete 20 Penetrating power 21 Ionization radiation 22  Ionization Ionizing radiation is produced by unstable 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. 23  Nuclear reactions Some radioisotopes contain nuclei which are highly unstable and decay spontaneously by splitting into 2 smaller nuclei. Such spontaneous decays are accompanied by the release of neutrons. 24  Detecting ionization radiation There are three main methods of detecting ionization radiation  Photographic method.  Scintillation method.  Geiger counter. 25 ionization radiation has been known to cause:  Skin cancer.  Bone cancer. And damage to bone cells.  Leukaemia.  Other types of cancer.  Damage to brain cells.  Eye cells.  Damage to other organ cells and tissues.  Genetic risk (which is more difficult to determine because it may appear after several generations). This type of risk causes damage to genes of the cell nuclei). 26 X-ray is also harmful; person must take precaution to avoid exposure. The effect of being exposure to high level of radiation kill the cells (this fact is used to treat cancer), so normally cancer cells is exposed to high energy radiation (X-Ray, ɣ radiation...) to destroy these cells. 27  The Effects of Radiation on the Cell at the Molecular Level  When radiation interacts with target atoms, resulting in ionization or excitation.  The absorption of energy produces damage to molecules by direct and indirect actions.  For direct action, damage occurs to atoms on key molecules in the biologic system. This causes functional alteration of the molecule.  Indirect action involves the production of free radicals whose toxic damage on the key molecule results in a biologic effect. 28 Thank you 29