1 / 32

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 :

anisa
Download Presentation

Spectroscopy of exotic nuclei Lecture 2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related