lecture 7

lecture 7 - 1/23/2012 Health Physics Principles EEE 498,...

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1/23/2012 Lecture 1 1 Health Physics Principles EEE 498, EEE 591 Lecture 7 Interaction of Radiation with Matter: Beta Particles Spring 2012, ASU R. Metzger, rlmetzger@asu.edu, BYEN335 Interaction of Radiation with Matter In order to understand radiation dosimetry, protection, shielding and therapy, it is important to know how radiation interacts with matter. Radiation may interact, directly or indirectly, with atomic nuclei, electrons or both. Health physicists need to know: The probability of interactions, The penetrating power, The radiation effects. The above depends on: Type of radiation, Energy of radiation, The nature of the absorbing medium. In most instances, interactions involve energy transfer. Lecture 7 2
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1/23/2012 Lecture 1 2 Beta Rays Range-Energy Relationship Attenuation of beta rays may be measured by a suitable beta-ray detector, such as a Geiger counter. It is shown that the beta-particle counting rate decreases rapidly at first and then, as the absorber thickness increases, slowly. Range: The end point in the absorption curve, where no further decrease in counting rate is observed. Lecture 7 3 Absorption curve (Al absorbers) of 210 Bi beta particles. Background counting rate Beta Rays Range-Energy Relationship (Cont.) Half thickness: The thickness of absorber which stops one half of the projectiles, e.g., beta particles. Rule of thumb: The absorber half- thickness is about one-eight of the range of beta rays. Figure on the right shows that the range of beta rays in matter is a function of the absorber density and energy of beta particles. The range depends on the number of absorbing electrons in the path of the beta ray and also to a lesser degree on the atomic number of the absorber. Lecture 7 4
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1/23/2012 Lecture 1 3 Units of Range Range can be displayed in: Unit of thickness (such as cm), Density thickness, t d (such as g/cm 2 ) t d g/cm 2 = ρ g/cm 3 x t 1 cm Example: The range of
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lecture 7 - 1/23/2012 Health Physics Principles EEE 498,...

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