Radiation Biology (VMPT403) Prof. Shittu - PDF

# U19ACADEMICCOMMITTEE ## Radiation Detection and Dosimetry - To understand the effects of ionizing radiation on biological systems: - You need to know the amount of radiation which the system is exposed to. - You need to know the pattern of dissipation of energy within the system. ## R...

# U19ACADEMICCOMMITTEE ## Radiation Detection and Dosimetry - To understand the effects of ionizing radiation on biological systems: - You need to know the amount of radiation which the system is exposed to. - You need to know the pattern of dissipation of energy within the system. ## RADIATION UNITS - Many different units have been proposed and used for the various radiation quantities. Some of the units which are in use today are briefly described below: ### 1. Roentgen (R) - Named after Wilhelm Conrad Roentgen, discoverer of x-rays in 1895. - A unit of exposure to ionizing radiation. - It is the amount of gamma or x-rays required to produce ions resulting in a charge of 0.000258 coulombs/kilogram of air under standard conditions. ### RAD - Is a unit of absorbed dose for any ionizing radiation. - One rad is 100 ergs absorbed per grams of any substance or 0.01 joule per kilogram. - The number of rads is approximately equal to the number of roentgen. - Rads is used for particulate as well as electromagnetic radiation. ### REM - This is a unit of dose equivalent numerically equal to the dose of in rads multiply by appropriate modifying factors such as RBE (or QF) or DF. - This was proposed to make allowances for the fact that the same dose in rads from different types of radiation does not necessarily produce the same degree of biological effect. - Where mixture of radiations occur, there is difference in biological effectiveness. ### Relative Biological Effectiveness (RBE) - This is a factor expressing the relative effectiveness of radiations with differing linear-energy-transfer of values, in producing a given biological effect. - It is now limited to use in radiobiology. - The RBE are usually experimentally derived values which pertain only to the system under study. ### DOSE DISTRIBUTION FACTOR (DE) - Is a factor expressing the modification of biological effect due to non-uniform distribution of internally deposited radionuclides. ### QUALITY FACTOR (QF) - Is another name for a linear energy transfer dependent factor by which absorbed doses are to be multiplied to account for the varying effectiveness of different radiations. - The unit is used for purposes of radiation protection and is similar to the RBE unit used in radiobiology. ### CURIE (Ci) - Is a unit of activity of a radioactive nuclide which is equal to 3.7 x 1010 radioactive disintegration per second. - It indicates the rate at which the atoms of radioactive material is decaying. ### SIEVERT (Sv) - This is the International System of Units (SI) derived unit of dose equivalent radiation that takes into account the relative biological effectiveness of different forms of ionizing radiation. - The SI unit for dose equivalent equal to 1 Joule/kilogram. - 1 Sievert = 100 rem. ### BECQUEREL (Bq) - One of three units used to measure radioactivity, which refers to the amount of ionizing radiation released when an element (such as uranium) spontaneously emits energy as a result of the radioactive decay (or disintegration) of an unstable atom. - 1 Bq represents a rate of radioactive decay equal to 1 disintegration per second. ## Relationship between Activity and Absorbed Dose ### EXTERNAL SOURCE - These are sources of radiation that is not contained within the material being exposed. - Alpha or beta rays are not ordinarily used for external radiation because of their relatively short path lengths in air - Gamma rays have a long path length in air, hence are used usually. - X-rays are also a common source of external radiation. - **Inverse Square Law**: State that the radiation intensity varies inversely as the square of the distance from the exposure. - It is a relationship that can be used with gamma sources. ### INTERNAL SOURCES - This is the estimation of radiation from a source that is contained within a system. - Radionuclides which emits alpha or beta rays are frequently used as internal emitters. - Because of the short path lengths of these radiations in tissues (usually 1 cm or less), it can usually be assumed that most of the energy has been absorbed within the specimen. ## Radiation Detection and Measurement - Several methods for detection and measurement of radiation exist. - **Use of Ionization Chambers**: operate due to ionization produced in them by the passage of charged particles. - **Scintillation detectors and luminescent dosimeters**: this works through excitation of atoms by ionizing radiation with a resultant luminescence. - **Chemical reactions**: this can be quantitatively related to the amount of radiation received by the system, and the heat production from radiation can be measured by calometric means. - **Latent images in photographic film and visible tracks in cloud or bubble chambers** mark the passage of an ionizing particle or photons etc. # U19ACADEMICCOMMITTEE