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Published byAmbrose Owens Modified over 9 years ago
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Decay
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W. Udo Schröder, 2007 Alpha Decay 2 Nuclear Particle Instability-Decay Types There are many unstable nuclei - in nature Nuclear Science began with Henri Becquerel’s discovery (1896) of uranium radioactivity and man-made: Types of decay: “weak” decays
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Discovery of Radioactivity W. Udo Schröder, 2007 Alpha Decay 3 Marie & Pierre Curie (1897- 1904) studied “pitchblende” Ra: powerful emitter Heavy nuclides (Gd, U, Pu,..) spontaneously emit particles. Mass systematics energetically allowed electrometer particles energetically preferred (light particles)
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Energy Release in Decay W. Udo Schröder, 2007 Alpha Decay 4 “Q-Value” for a Decay: Q=B( 4 He)+B(Z-2,A-4)-B(Z,A) Shell effect at N=126, Z=82 Odd-even staggering Z=82 Geiger-Nuttall Rule: Inverse relation between -decay half life and decay energy for even-even nuclei
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Examples: Alpha Decay Schemes/Spectra W. Udo Schröder, 2007 Alpha Decay 5 Short-range particles Long-range particles Many emitters: E ~ 6 MeV (short range) Heavy emitters also: E ~ 8 MeV (long range)
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Solution to a Puzzle: Tunneling the Coulomb Barrier W. Udo Schröder, 2007 Alpha Decay 6 Nuclear Potential -Nucleus Coulomb Potential Answered Puzzle: If nucleus stable : t 1/2 ∞ If nucleus unstable : t 1/2 0 Not found in nature Resolution of Puzzle Quantum meta-stability (if nucleus has intrinsic structure, P =1): Gamov: Intrinsic wave function “leaks” out Superposition of repulsive Coulomb potential + attractive nuclear potential creates “barrier” R Th =9 fm U Th = 28 MeV E = 4MeV
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Alpha Decay W. Udo Schröder, 2007 7 Quantal Barrier Penetration Particle escape probability (system decay) depends on barrier height & thickness the number of states E, U General solution of Schrödinger Equ.: Lin. Comb. of exponentials 0 d x 2 1 3 U E E
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Barriers of Arbitrary Shape W. Udo Schröder, 2007 Alpha Decay 8 Approximate by step function UiUi U(r) R1R1 R2R2 Application: Z 1 =2, Z 2 =Z-2
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The Geiger-Nuttal Rule W. Udo Schröder, 2007 Alpha Decay 9 half life vs. energy (years)
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Angular Momentum and Parity in Decay W. Udo Schröder, 2007 Alpha Decay 10 Solve 1-D Schrödinger Equ. For -daughter system with effective radial potential (Coulomb + centrifugal) conserved angular momentum Spin/parity selection rule for transitions: = 0 most probable decay Higher values hindered significantly because of small T Estimate range of -values from E and nuclear radii !
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Decay Patterns W. Udo Schröder, 2007 Alpha Decay 11 From Krane, Introductory Nuclear Physics 0 keV Guess some final nuclear spins I 479 keV Decay of 251 Fm
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Cluster Decay W. Udo Schröder, 2007 Alpha Decay 12
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Experimental Data W. Udo Schröder, 2007 Alpha Decay 13 BB
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Alternative W. Udo Schröder, 2007 Alpha Decay 14
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