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Experimental Historical Introduction

Experimental Historical Introduction. Yorick Blumenfeld Institut de Physique Nucléaire – Orsay yorick@ipno.in2p3.fr. Experimental Historical Introduction. Coulomb Force :The Rutherford Experiment The Strong Nuclear Force Nuclear Masses and Binding Energies

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Experimental Historical Introduction

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  1. ExperimentalHistorical Introduction Yorick Blumenfeld Institut de Physique Nucléaire – Orsay yorick@ipno.in2p3.fr Unité mixte de recherche CNRS-IN2P3 Université Paris-Sud91406 Orsay cedex Tél. : +33 1 69 15 73 40 Fax : +33 1 69 15 64 70 http://ipnweb.in2p3.fr

  2. ExperimentalHistorical Introduction • Coulomb Force :The Rutherford Experiment • The StrongNuclear Force • Nuclear Masses and Binding Energies • Nuclear + Coulomb: The Liquid Drop Model • The Spin Orbit Interaction: MagicNumbers and the Shell Model • Transfer Reactions • Charge Independence and Isospin • N-N scattering • The YukawaPotential and the pion • The weak force • Beta radioactivity • The discovery of the neutrino • Summary

  3. J.J. Thompson’sPlum Pudding Model(1900)

  4. The Rutherford ExperimentElectric force FC = zZe2/r2

  5. Rutherford cross section (Ta ~ 5 MeV) dWsolid angle dndetectedparticles/second I particles/second N nuclei/cm2 Geometrical cross section: Rutherford cross section

  6. Elastic cross section Ta ~ 22 MeV There is a nuclear force ! See Lecture by Alessia di Pietro

  7. Nuclear Masses and Binding Energies The interestingquantityis B but one measures masses soprecisionis important

  8. Nuclear Mass Measurements: MagneticRigidity Position Sensitive Detector Magnetic spectrometer Ion Source Wien Filter

  9. Nuclear mass measurement:NuclearReactions Energy conservation Momentum Conservation

  10. Heavy Ion Reactions 70Zn(14C,16O)68Ni M. Bernas et al.; Phys. Lett. 113B (1982) 279 See Dieter Ackerman’s lecture 60 years of IPN M. Assié, Y. Blumenfeld

  11. Nuclear Mass measurements

  12. Results 10 B/A (MeV) 5 A The bindingenergy per nucleonis constant to first order: The strong force is short range. If itwas long range then B wouldbeproportional to A2. The range is of order of 1.5fm.

  13. The liquid drop model 16 Surface BULK E/A (MeV) Asymmetry Hans Bethe Coulomb Carl vonWeizäcker 8 Total A 100

  14. Magicnumbers: Where quantum mechanicscomesintoplay Z 28 50 82 126 N 28 50 82 126 Nuclei withmagicnumbers of protons and neutrons: more bound, highenergy of excited states, sphericalshape ….. Explainedthrough the nuclearshell model.

  15. The Nuclear Shell Model Assumption: nucleonsfeel a one body potentialcreated by all othernucleons Maria Goeppert Mayer Hans Jensen

  16. 126 82 50 28 20 8 2 The Spin-Orbitpotential

  17. Testing the shell model: Transfer reactions proton deuteron Example SeeSusumuShimoura lecture

  18. 1 2 4 3 4 3 2 1 2p1/2 1f5/2 2p3/2 1f7/2 20 1d3/2 2s1/2 1d5/2 8 8 8 8 8

  19. Angular Distributions > l transfer L=1 L=3 C.K. Bockelman and W.W. Buechner Phys. Rev 107 (1957) 1366 L=1 L=2 or 3

  20. Charge independence of the nuclear force • Heisenberg, Condon and Cassenpostulatedthatnuclear forces are charge independent , thatis n-n, n-p and p-p interactions are the same (except for the Coulomb force). • Neutron-proton and proton-proton scatteringproperties are verysimilar if the Coulomb force isfactored out. • Mirror nuclei have verysimilarlevelschemes.

  21. LevelSchemes of Mirror Nuclei

  22. ISOSPIN Neutron and proton are the sameparticle (nucleon) with an Isospin t=½ differentiated by the projection of their Isospin on an arbitrary axis : t3 (n) = 1/2 and t3 (p) = -1/2 . The formalismis the same as for spins. ISOSPIN is a good quantum number for the nuclear interaction but not for the Coulmb interaction. For a nucleus and Example for 25Mg T3 = ½ (N-Z) = ½ and so

  23. ISOSPIN Multiplets

  24. Nucleon-Nucleonscattering N-N potentialshape

  25. The Yukawapotential In Quantum fieldtheory a force is due to the exchange of a boson The boson should have a mass of around 140 MeV. ShortlyafterYukawa’shypothesissuch a particlewasfound in 1936 but itturned out to be the muon. The pion wasonlydiscovered in 1947. That’swhy in oldtextbooksyoucanfindreference to the mu meson! For the e.m. interaction the boson is the photon and for the weak interaction the W and Z

  26. Radioactivity Alpha Decay Fission Gamma Decay b+ b- Beta decay

  27. Postulation of the neutrino (1930)

  28. Radioactivity Alpha Decay Fission Gamma Decay b+ b- Beta decay

  29. Discovery of the neutrino (1956)

  30. Summary

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