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Lesson7 - Lesson 07 Radioactivity 01 MP200 Radiation...

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Unformatted text preview: Lesson 07 Radioactivity 01 MP200 Radiation Physics - 2010 Duke Medical Physics Graduate Program 1 Introduction In this lesson, we will study, the processes and kinematics of, , and decays, Electron Capture, Internal Conversion and, Auger Electron Radioactivity The spontaneous disintegration or rearrangement of the internal structure of an un- stable nucleus by emitting particles or radiation is called Radioactivity. Emitted particles and radiation from radioactivity are collectively called rays. There are three kind of rays in natural occurring radioactivity. rays, rays (electrons and positrons), rays rays are helium nucleus and can be blocked by a 0 . 01 mm of lead. rays are electrons or positrons and can be blocked by a 0.1 mm of lead. rays are the most penetrating and can pass through a 100 mm thick lead. In radioactive decay, Mass, energy, electric charge, linear momentum angular momen- tum, and nucleon numbers should be conserved. Example: Initial amount of charge = final amount of charge after decay. Initial nucleus called parent emits a particle and produces another particle called the daughter . Daughter may be the same nucleus, in lower energy state or an entirely new nucleus. 2 decay The process of ejecting an alpha particle from a nucleus is called decay. The atomic number of the parent P decreases by 2, and the mass number decreases by 4, when the daughter D is produced. A Z P- A- 4 Z- 2 D + 4 2 He Example: 226 88 Ra- 222 86 Rn + 4 2 He Kinematics of decay Let us assume, the decay occurs in a system where the parent is at rest. P- D + From the conservation of energy, M p c 2 = M D c 2 + M c 2 + K D + K K D ,K = Kinetic energies, and M P , M D ,M = Masses of particles Since, K D + K 0, M p M D + M Q- value The energy released is the disintegration energy, and it is called the Q- value. This value is equal to the difference between the final and the initial kinetic energies of the system. Q = K D + K Q = ( M p- M D- M ) c 2 From conservation of linear momentum and the Q value, 3 Figure 1: decay M v = M D V (1) Q = 1 2 M v 2 + 1 2 M D V 2 (2) Removing V from (1) and (2), Q = 1 2 M v 2 M D + M M D Since, K = 1 2 M v 2 K = M D Q M D + M and, K D = M Q M D + M Since, M D + M A K = A- 4 A Q Decay Scheme The nuclear transformation from parent to daughter can easily be described by a decay-scheme diagram. This diagram includes the decay mode, branching ratio, and the energy transitions. 4 Conventions: 1. Arrows slanting to the left side indicate decrease in Z. 2. Arrows slanting to the right side indicate the increase in Z....
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This note was uploaded on 10/30/2010 for the course MP 200 taught by Professor Guna during the Fall '10 term at Duke.

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Lesson7 - Lesson 07 Radioactivity 01 MP200 Radiation...

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