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Spectroscopy of exotic nuclei Lecture 2

Spectroscopy of exotic nuclei Lecture 2. Shell modifications (continued). How to find shell closures. Shell closure. Fig. by R.F. Casten. ISOLTRAP. Needed accuracy to test nuclear models : <100 keV /c 2 = 10 -1 MeV /c 2 Mass of A~100 nucleus :

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Spectroscopy of exotic nuclei Lecture 2

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  1. Spectroscopy of exotic nuclei Lecture 2 Shell modifications (continued) R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  2. How to find shell closures Shell closure Fig. by R.F. Casten R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  3. ISOLTRAP Neededaccuracytotestnuclearmodels: <100 keV/c2 = 10-1MeV/c2 Massof A~100 nucleus: m  A · mp  A ·1000 MeV/c2 = 105MeV/c2 measurement  Dm/m = 10-6 purification Experiments are performed with bunches of a few tens of ions. bunching Dn/n ~ 4∙10-7 175 keV A. Herlert, et al., Int. J. Mass Spectrom. 251, (2006) 131 R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  4. time SchottkyMassSpectrometry 4 particles with different m/q Y. Litvinov, GSI R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  5. Sin(w1) Sin(w2) w4 w3 w2 w1 Sin(w3) time Sin(w4) SchottkyMassSpectrometry Fast Fourier Transform Y. Litvinov, GSI R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  6. SchottkyMassSpectrometry (~190 keV) R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  7. ILIMA mass measurements mass surveys Are mass measurements sufficient?  130Cd R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  8. Probing shell closures: Decay Spectroscopy N=82 b-decay Q-value (ISOLDE):  130Cd less bound  Quenching of N=82 shell ? I. Dillmann, PRL91 (2003) 162503 • no shell quenching • information on excited states essential!! A. Jungclaus et al., PRL 99, 132501 (2007) R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  9. Shell modification through softer potential Pfeiffer et al. T.R. Werner, J. Dobaczewski, W. Nazarewicz, Z. Phys. A358 (1997) 169 Possible signatures:  new shell gaps (e.g. N=70 in 110Zr)  reduction of spin-orbit splitting in neutron-rich nuclei  increased neutron skin R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  10. Shell modification through residual interaction Effective single particle energies N=20 unbound bound 24O doubly magic 32Mg deformed T. Otsuka et al. Z=8 O. Sorlin, M.G. Porquet, Prog. Part. Nucl. Phys. 2008 ... whatistheheaviestboundoxygen isotope???? R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  11. Non-existence of 28O (Z=8,N=20) H. Sakurai et al., Physics Letters B 448 (1999) 180 RIPS@RIKEN Position x-y ètrajectoryBrèp, A/Z TOF èv èA dE/dxèZ R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  12. The neutron drip-line O  F: 1 extra proton can bind 6 more neutrons Is 24O doubly magic? Otsuka et al., arXiv:0908.2607v1 [nucl-th] R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  13. Probing single-particle structure with fast beams from A. Gade • Knockout reaction • peripheral collision • relativistic energies (250-1000 AMeV) • possible with few particles/s p|| • identify (Z,A) event by event • resolve g - energies despite large Doppler shift •  identify individual ex. states • Momentum distribution: • L of knocked-out particle • Cross sections: • Single particle occupations R. Kanungo et al., PRL 102 (2009) 152501 R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  14. 24O knock-out experimentatthe GSI FRS FRS operation in 'dispersion matched mode' → direct momentum measurement at S4 6.347 g/cm2 Be 48Ca 1A GeV Excellent agreement with predictions for N=16 shell closure carbon 4.05 g/cm2 R. Kanungo et al., PRL 102 (2009) 152501 R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  15. Reduced spin-orbit or tensor force? j’> j’< j> neutrons j< protons T. Otsuka et al., PRL 95 (2005) 232502 11/2- 7/2+ 1h11/2 protons 1g7/2 protons Z=51 Sb isotopes J.P. Schiffer et al., PRL 92 (2004) FRIB 1h11/2 neutrons T. Otsuka et al., PRL 97 (2006) 162501 R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  16. Between Z=8 and Z=20: Island of Inversion Excited states pure sd-shell deformed  Indications of deformation Y. Utsuno et al., PRC60 (1999) 054315 R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  17. Island of Inversion First introduced 1990: Warburton, Becker, Brown, PRC41,1147  nuclei with ground state dominated by neutron excitations from sd to fp shells (intruder states, deformed) G. Neyens R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  18. Experimental Program for Island of Inversion • Goal: • map the island of inversion and investigate the transition from the ‘normal’ region into the island • Determine properties of ground states and excited states: • energies, spins, E.M. moments, deformation, occupations, ... • Experimental access: • Coulomb excitation  transition moments, deformation • beta-decay studies  spins/parities • magnetic moments, g-factors  wave function, Ip • quadrupole moments  static deformations • reaction studies  orbital angular momenta, spectroscopic factors R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  19. Coulomb excitation Excitation cross-section Integral over trajectory Structure information from reduced transition strength: Deformation Quadrupole moment R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  20. Intermediate energy Coulomb excitation T. Glasmacher, Annu. Rev. Nucl. Part. Sci. 1998.48:1-31 Doppler-correction Au 40S 20-50 MeV/u Au • Possible complications: • a) Need to separate EM interaction from nuclear interaction • select small scattering angles  large distance between nuclei • b) Possible feeding from higher lying 2+ states R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  21. Collectivity of 32,34Mg T. Motobayashi et al. Phys. Lett. B 346 (1995) 9. K. Yoneda et al., Phys. Lett. B 499 (2001) 233 150 Without N=20 shell N=20 100 B(E2; 2+ 0+) [e2fm4] 50 With N=20 shell 0 30 32 38 36 34 Ar S Si Mg Ne 32Mg: E(4+)/E(2+) = 2.6 34Mg: E(4+)/E(2+) = 3.2 Rotor: E(4+)/E(2+) = 10/3 Secondary fragmentation of 36Si beam R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  22. Island of Inversion H. Scheit R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  23. Structure of 31Mg COLLAPS • From laser spectroscopy: • Ground state is 1/2+ state • Must be intruder dominated • Next step: •  Check structure of excited states R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  24. The COLLAPS set-up at ISOLDE Collinear Laser Spectroscopy • Mg+ ions are polarized through optical Zeeman pumping  nuclei are polarized • rotate polarization and implant ions into MgO crystal in strong magnetic field • scan of hyperfine structure by tuning ion velocity at fixed laser wavelength • HF resonances are observed via beta decay asymmetry of polarized 31Mg • Hyperfine structure allows for spin determination • g-factor is measured via beta-NMR: • RF Field at the Lamor frequency will resonantly destroy polarization and thus beta-asymmetry •  Scan RF frequency and measure beta-asymmetry R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  25. Results for 31Mg Ground state properties: I = 1/2 g = 1.7671(3)  Can only be explained by deformed intruder configuration Neyens et al., Phys. Rev. Lett. 94, 022501 (2005) R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  26. Transfer reactions • (d,p), (3He,d): Stripping of neutron or proton from light ion • (p,d), (3He,a): Pick-up of neutron/proton by light ion • Example • d + 90Zr  p + 91Zr or90Zr (d,p) 91Zr Other examples:(d,p), (a,3He)…(p,d), (3He, a)…(3He, d), (a, t)…(d,3he), (t,a)… R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  27. Example– 54Fe(d,p)55Fe Munich Q3D 25 MeV deuterons 5 keV FWHM counts 55Fe Energy (keV) R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  28. d(30Mg, 31Mg)p - first attempt at ISOLDE Angular distributions not sufficiently characteristic R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  29. Transfer set-up T-REX inside MINIBALL efficiency of full 4p array: 62% V. Bildstein, K. Wimmer • T-REX position sensitive silicon detector array: • forward barrel (DE-E): 140/1000 μm • backward barrel/CD: 500 μm silicon • 3◦ − 5◦ angular resolution • energy resolution of 60 keV (backward) to 2 MeV (forward) at 3 MeV/u R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  30. Limitation: Energy resolution Example: d(54Fe,p)55Fe reaction at 2.4 MeV/u JLab = 150° (QCM = 17°) • Ti target foil loaded with Deuterium 70 keV FWHM 55Fe DEx=411 keV DEp~220 keV Poor spectroscopic energy resolution of ~ 150 keV R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  31. Normal vs. Inverse kinematics Normal kinematics • Thin targets (100 mg/cm2) + intense beams (~1010pps)  high resolution spectroscopy of projectile with spectrograph Inverse kinematics • Low beam intensity (> 104pps)thicker targets (1 mg/cm2) • Kinematic broadening of heavy projectile poor resolution • Detection of light target-like particle  Need large angular coverageSi-Detector array • Energy resolution limited due to energy loss in target (beam and ejectile)  Gamma detection needed for spectroscopy BUT:Gamma-emission at high velocities  good Doppler correction needed  segmented Ge-detectors R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

  32. Modification of shell structure Ti 46 48 49 50 47 Sc 45 classic shell closures Ca 43 40 42 44 46 48 54 Predicted new shell closures K 39 41 Ar 36 38 40 Cl 35 51 37 S 32 33 34 36 P 31 47 Si 28 29 30 44 Al 27 43 Mg 24 25 26 32 40 Na 23 36 20 21 22 34 Ne 19 31 F Island of inversion 18 24 O deformed g.s. R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 2

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