Lecture13-16

O dpdt we can put all the ns on the ler side and t on

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Unformatted text preview: energy gains (per nucleon) by fusing hydrogen into helium. Fusion Fission 230 MeV Per nucleus 22 Abundance of Elements Closed shells Hydrogen and some Helium made in big bang. Up to Ni made in stars Above Ni, made in supernovae Peaks and sharp drop- offs understandable in shell model. Pb (lead) has closed shells for both p and n. Stable nuclei end just above Pb. Thorium and Uranium decay with life;mes in the billions of years, ul;mately producing lead or bismuth. 23 Clicker: Shell Model u༇  Which statement about the nuclear shell model is false? A) Nuclei with a closed shell have relatively larger abundances. B) The nuclear shell model works because many neutrons can be in the same state. C) Nuclei with a closed shell of n or p are more tightly bound. D) Closed shells of n or p are spherically symmetric and thus easier to understand. E)None of the above. 24 NMR and MRI u༇  The proton and neutron are spin ½. u༇  It is possible to observe transi;ons between two spin states using NMR u༇  The magne;c field splits the states u༇  RF signal is send in to populate upper state u༇  RF signal is detected to measure rate of transi;ons. u༇  Vary B field as a func;on of depth to get 1D picture u༇  scan RF input to get other 2D (or measure direc;on of output) u༇  MRI Natural Radioac;vity In 1896 Henri Becquerel (1852–1908, French physicist) accidentally discovered that uranyl potassium sulfate crystals emiFed an invisible radia;on that could darken a photographic plate when the plate was covered to exclude light. u༇  There are three element present in nature that have decay chains with several radioac;ve nuclei. u༇  Thorium is the most abundant. u༇  26 Radioac;ve Decay Rates u༇  Each radioac;ve nucleus has the same probability to decay in a short ;me interval dt. o  dP/dt=λ We can put all the Ns on the leR side and t on the right and integrate this equa;on. u༇  The number of radioac;ve nuclei decreases exponen;ally in ;me. u༇  The average life;me is 1/λ. u༇  27 Radia;on Radioac+ve Sources Each nucleus decays randomly (QM) with some average life;me. u༇  Number of source nuclei leR decreases exponen;ally. u༇  Ac;vity of source also decreases exponen;ally. u༇  Units of Radia+on u༇  Ac;vity o  1 becquerel = 1 decay per second. o  (1 curie = 37 gigabecquerel) u༇  Dose o  1 gray = 1 Joule/kg o  (1 gray = 100 rad) u༇  Biological dose equivalent o  emphasize damage of alpha, neutron… o  1 sievert = 1 gray for x- rays o  (1 sievert = 100 rem) o  6 sievert (full body) is 50% kill dose o  natural radia;on 0.01 sievert per year o  rad worker dose limit 0.05 sievert per year 28 Clicker: Half Life u༇  If the probability of a radioac;ve isotope to decay in one second is 10- 14, what is the half life of that isotope? A) 1014 s. B) 6.93 X 1013 s. C) 1.44 X 1...
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