1. Decay

2. 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

3. 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)

4. 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

5. 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)

6. 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

7. 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

8. 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

9. The Geiger-Nuttal Rule W. Udo Schröder, 2007 Alpha Decay 9  half life vs.  energy (years)

10. 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 !

11.  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  

12. Cluster Decay W. Udo Schröder, 2007 Alpha Decay 12

13. Experimental Data W. Udo Schröder, 2007 Alpha Decay 13 BB

14. Alternative W. Udo Schröder, 2007 Alpha Decay 14