Exam_1_2009_Solutions-1

Exam_1_2009_Solutions-1 - 22.01 Radiation Effects and Uses...

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22.01 Radiation Effects and Uses Quiz #1 Professor J.C. Yanch 15 October 2009 Name _________________________ Instructions: This examination consists of 8 (eight) questions. Points awarded for each correct answer are noted on the left side of each question. A total of 100 points will be awarded. Please write all answers on the exam paper. If an answer extends to the back of page, please indicate that this is so. This is a closed book examination. 1. Identify the daughter products (by specifying, where possible A,Z,N and the chemical element) of the following radionuclides, given their mode of decay. Briefly state (e.g. “too many protons”) why the isotope would decay in the indicated way. a) 90 Sr ( β - ) b) 238 U ( α ) c) Pm 147 61 ( β - ) 51 51 39 Y 144 234 90 Th 85 147 62 Sm too many neutrons too many nucleons too many neutrons 12 d) 252 Cf(SF) e) 78 Br ( β + ,EC) f) 99m Tc( γ ) two medium-A nuclei eg. 60 100 40 92 150 58 Zr Ce 44 78 34 Se 56 99 43 Tc too many nucleons too many protons E* too large [Note: The A of 252 is shared between the two fission fragments plus either 2 or 3 neutrons. ]
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2. a) Where does fluorescent radiation come from? Explain in words with the help of a diagram. In atoms with electron vacancies in the inner shells, electrons from higher shells can fill these vacancies. The difference in energy between the higher energy shell it came from, and the lower energy (inner shell) it dropped into, is given off as a photon. This is fluorescent radiation. b) What is another name for this type of radiation? Since the energy of the emitted photons is specific to a particular atom and the spacing between its energy levels, this radiation is characteristic of that atom and hence it is called “characteristic radiation”. c) Name and describe the process that competes with fluorescence. 8 Auger electron emission competes with fluorescence. This is a process whereby the difference in energy between the higher and lower energy shells is transferred to another electron and the electron is ejected. This is an Auger electron. We now see two vacancies in the atom. This process can continue resulting in several Auger electrons being emitted and an atom with several positive charges.
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3. 136 Cs (half-life = 13.7 d) decays ( β - ) into 136m Ba (half-life = 0.4 s), which decays ( γ ) into stable 136 Ba: 136 Cs 7 . 13 d - β 136m Ba s 4 . 0 γ
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This note was uploaded on 03/09/2010 for the course 22 22.01 taught by Professor Smith during the Fall '09 term at MIT.

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Exam_1_2009_Solutions-1 - 22.01 Radiation Effects and Uses...

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