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Examples of nuclear structure observables with fast beams Discovery of new isotopes

In-beam gamma-ray spectroscopy with fast beams of rare isotopes Experiments to elucidate the structure of very exotic nuclei Thomas Glasmacher National Superconducting Cyclotron Laboratory Michigan State University. Examples of nuclear structure observables with fast beams

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Examples of nuclear structure observables with fast beams Discovery of new isotopes

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  1. In-beam gamma-ray spectroscopy withfast beams of rare isotopesExperiments to elucidate the structure of very exotic nucleiThomas GlasmacherNational Superconducting Cyclotron LaboratoryMichigan State University • Examples of nuclear structure observables with fast beams • Discovery of new isotopes • The boundaries of the Island of Inversion • Collectivity in silicon and sulfur towards N=28

  2. Stable nuclei are well-described with closed-shell (so-called “magic”) nuclei as key benchmarks Rare isotopes show evidence for disappearance of canonical shell gaps, appearance of new shell gaps, reduction of spin-orbit force The most exotic nuclei accessible (largest N/Z ratio) are light nuclei and they have low beam rates New precision techniques have been developed in past decade to enable spectroscopy of these most exotic nuclei Experimental task: Quantify changes encountered in rare isotopes and measure with defined certainty observables that are calculable and can be used to discriminate between theories Goal: Develop predictive theory of atomic nuclei and their reactions

  3. In-flight production of rare isotopes Driver accelerator (v = 0.25-0.6 c) • Fragment separator (A1900 NSCL, FRS GSI, BigRIPS RIKEN, ALPHA spectrometer/LISE GANIL) • Identification and beam transport • Stopped beam experiments, reaccelerated beam experiments • Fast beam experiments • Secondary reaction • Reaction product identification (S800 spectrograph, CATE/Aladin, Silicon telescopes/TOF wall, SPEG) Reaction product identificationS800 spectrograph Identification and beam transport Fragment separatorA1900 fragment separator

  4. 65% of the produced 78Ni transmitted Fragments at production target Fragments at focal plane Fragments at achromatic degrader In-flight production of rare isotopesExample: 78Ni from 86Kr at NSCL Driver accelerator • Fragment separator (A1900 NSCL, FRS GSI, BigRIPS RIKEN, ALPHA/LISE GANIL) • Identification and beam transport • Stopped beam experiments • Fast beam experiments • Secondary reaction • Reaction product identification (S800 spectrograph, CATE/Aladin, Silicon telescopes/TOF wall, SPEG)

  5. Stopped beam experiments Possible experiments and quality of observables depend on number of beam particles * Discovery (few particles total) Half live(few ten particles) Mass (few hundred particles) Fast beam experiments Possible experiments and quality of observables depend on luminosity Interaction radii(few particles per hour) g-factors(hundreds of particles per second) Fast beam experiments (cont’d) Excited state energies * Multi-nucleon removal(hundreds of particles per second) Excited state energies, transition matrix elements * Inelastic scattering: Coulomb excitation, p-, a-scattering(ten particles per second) Lifetimes from g-ray line shapes(hundreds of particles per second) Occupation numbers * Single nucleon removal(particles per second) Two-nucleon removal(hundreds of particles per second) * Nucleon addition(hundreds of particles per second) Examples of observables in experiments within-flight produced exotic beamsRates are within 1-2 orders of magnitude depending on implementation and structure of nucleus

  6. NR = NT× NB ×s NR reaction rate (yields observable) NT atomic density of target NB beam rate s cross section (given by nature) Fast-beam g-ray spectroscopy at rates of a few nuclei per second • Fast exotic beams allow for • event-by-event identification and trigger • efficient detection of recoiling beam particles due to kinematic focusing • thick secondary targets (100-1000 thicker than at low energy) • Strategy: Use of photons to indicate inelastic scattering, measure particle-g coincidences • Example • s = 100 mbarn • NT = 1021 cm-2 • NB = 3 Hz • NR = 26/day = 3×10-4 Hz scatteredbeam beam target

  7. Direct reactions with heavy ions and coincident g-ray spectroscopy M. Ishihara, Nucl. Phys. A 400 (1983) 153c

  8. Direct reactions with heavy ions and coincident g-ray spectroscopy M. Ishihara, Nucl. Phys. A 400 (1983) 153c

  9. Intermediate-energy Coulomb excitation of 32MgLarge transition matrix element indicates breakdown of the N=20 shell gap sCoul = 87 mb • B(E2↑) = 454(78) e2fm4 = <0+||O(2)||2+> Scattering angle N 12 14 16 18 20 Experiment: Max.  determines min. impact param. Valence nucleonmodel Impact parameter Shell model T. Motobayashi et al., Phys. Lett. B346 (1995) 9 T.G. Ann. Rev. Nucl. Part. Sci. 48 (1998) 1

  10. Active programs at GANIL, GSI, MSU and RIKEN Published measurements to elucidate N=8, 20, 28, 32, 34, N=Z=36, light tin isotopes, … Single-step process Sensitive to E1, E2, E3 excitations Results agree with prior measurements where available Adopted and measured B(E2) values for stable nuclei B(E2) values fromdifferent methods for 26Mg Intermediate-energy Coulomb excitation Diff. btw. measured and adopted B(E2) (%) J. Cook et al., Phys. Rev. C 73 (2006) 024315.

  11. Shape of recoil momentum distribution of the A-1 fragment is measured and sensitive to l-value of knocked out nucleon Individual final states are tagged by g-rays Spectroscopic factors are determined from the population of excited states in the A-1 fragment. Wavefunction spectroscopy with knock-out reactions P4-1 (Wed) P.G. Hansen and J. A. Tostevin, Ann. Rev. Nucl. Sci. 53 (2003) 219

  12. Breakdown of the N=8 shell gap in 12Be12Be ground state only 32% n(1s1p)8 and 68% n(1s1p)6-(2s,1d)2 12Be  11Be+n+g 5/2+ d5/2 p1/2 17.5(26) mb 1/2- s1/2 32.0(47) mb 1/2+

  13. C. Thibault et al: PRC 12 (1975) 64631,32Na, local increase of S2n N=20 shell gap decreased X. Campi et al: NPA 251(1975) 193explained by deformation via filling of n(f7/2) C. Detraz et al: PRC19 (1979) 16432Na  32Mg b-decay, low 2+ in 32Mg E. Warburton et al: PRC 41 (1990) 1147Z=10-12 and N=20-22 have ground state wavefunctions dominated by n(sd)-2(fp)+2 configurations T. Motobayashi et al: PLB 346 (1995) 9large B(E2;0+ 2+) in 32Mg See also V. Tripathi et al. Phys. Rev. Lett. 94 (2005) 162501 (2005) G. Neyens et al. Phys. Rev. Lett. 94 (2005) 022501 (2005) A. Obertelli et al., Phys. Lett B 633 (2006) 33 H. Iwasaki et al., Phys.Lett. B 620 (2005) 118 Exploring the boundaries of Island of Inversion • Single-neutron removal to look for negative parity states, indicating the presence of f7/2 intruder configurations in the ground state of the parent: (30Mg,29Mg+g) (26Ne,25Ne+g) (28Ne,27Ne+g) • (38Si,36Mg+g) two-proton removal

  14. 25Ne level structure known A.T. Reed et al., PRC 60 (1999) 024311 S. Padgett et al., PRC 72 (2005) 064330 25Ne is well-described in sd shell with no evidence for intruder states below 3 MeV No evidence for intruder configurations in the ground state wave function of 26Ne Single-neutron removal from 26,28Ne and 30Mg • Island of inversion is growing J.R. Terry et al., Phys. Lett. B 640 (2006) 86

  15. Many experiments at GANIL (MUST detector) Few experiments at MSU Thin target to avoid angular and energy straggeling of low-energy protons Proton scattering in inverse kinematics Normal kinematics Inverse kinematics F. Maréchal et al., PRC 60 (1999) 034615 p(56Ni,p’) at GSI G. Kraus et al., PRL 73 (1994) 1773

  16. Thick-target g-tagged inelastic proton scatteringPioneering experiment at RIKEN p(30Ne,30Neg)Y. Yanagisawa et al. PLB 566 (2003) 84 • Inelastic p scattering using two cocktail beam settings to study chains of isotopes accessible in a consistent approach • Determine excited state energies and collectivity towards N=28 • Univ. Tokyo, RIKEN, Rikkyo Univ., Michigan State Univ. collaboration Z Sulfur 40Si Silicon • RIKEN/Kyushu/Rikkyo LH2 target:H. Ryuto et al., NIM A 555 (2005) 1 • 30 mm diameter • 9 mm thick, nominal • Negligible contaminant reactions 36Si N C.M. Campbell Ph.D. thesis (2007) Michigan State Univ.

  17. Evolution of 2+ energies towards N=28 40Si Above Z=20Ti, Cr and Fe 986(6) keV Below Z=20Si, S and Ar • 1.5 million 40Si beam particles • sp,p’= 20(3) mb • ~30 counts in the photopeak • Low energy indicative of neutron collectivity in 42Si C.M. Campbell et al., PRL 97 (2006) 112501

  18. Evolution of 2+ energies towards N=28 40Si Above Z=20Ti, Cr and Fe 986(6) keV Below Z=20Si, S and Ar • 1.5 million 40Si beam particles • sp,p’= 20(3) mb • ~30 counts in the photopeak • Low energy indicative of neutron collectivity in 42Si Discovery of low-lying 2+ state in 42Si at GANIL B. Bastin, S. Grévy et al.arXiv 0705.4526 F9-2 (Wed) C.M. Campbell et al., PRL 97 (2006) 112501

  19. Two additional g-rays in fragmentation channel 42P-p-n States at 1.62(1) MeV and 1.82(1) MeV? Not enough statistics to test if the two transitions are in coincidence Independent of the sequence, the second excited state is low in energy In the shell model second excited state is ph-excitation across N=28 Low energy supports narrowing of the N=28 gap in 40Si Higher excited states in 40Si C.M. Campbell et al., PRL 97 (2006) 112501

  20. Evolution and character of collectivity Prior data from F. Maréchal et al, PRC 60, 034615 (1999) P.D. Cottle et al., PRL 88, 172502 (2002) N N • Enhanced collectivity towards N=28 in silicon • Sulfur transitions from vibrational mid-shell to rotational towards N=28 • Silicon vibrational mid-shell Rotational limit Sulfur Silicon Vibrational limit C.M. Campbell Ph.D. thesis (2007) MSU

  21. Traditionally performed in normal kinematics at lower beam energies, e.g. (d,n), (3He,d), (a,t), … Few mb cross sections observed at intermediate energies Proton well-bound in 9BeSp(9Be) = 16.9 MeV 8Li has only one bound excited state Single-proton addition Beam identification Reaction product identification

  22. Measure coincident g-rays and particle momenta

  23. Resulting strength distribution compared to normal kinematics measurement A.M. Mukhamedzhanov et al. Phys. Rev. C 73 (2006) 035806 A. Gade et al. in preparation (2007)

  24. 4He(22O,23Fg) 2000/sProton addition 4He(23F,23Fg) 550/sInelastic scattering 4He(24F,23Fg) 470/sneutron-knockout 4He(25Ne,23Fg) 1200/s two-proton knockout Structure of 23F: Multiple reactions in one experiment~35 MeV/nucl,100 mg/cm2 liquid helium target at RIKEN A. Michimasa et al. Phys. Lett. B 638 (2006) 146

  25. Summary and outlook • Discovery of new isotopes 40Mg, 42Al, 43Al, 44Si at NSCL • In-beam gamma-ray spectroscopy with fast beams • Enables further scientific reach through luminosity gains of 100-1000 for a given driver accelerator • Has in past decade transitioned into a worldwide effort with a set of robust experimental techniques that have contributed to many discoveries • As new powerful drivers have come into operation in Japan, are under construction in Europe, and are being considered in United States (→ Prof. Tribble J4-4 Wed) this field will gain 1-2 orders of scientific reach from new detectors such as GRETA and AGATA www.nscl.msu.edu/isf GRETA, I.Y. Lee, Lawrence Berkeley Lab GRETINA in front of S800

  26. Collaborators P. Adricha), N. Aoic), D. Bazina), M. D. Bowena,b), B. A. Browna,b), C. Campbella,b),J. M. Cooka,b), D.-C. Dincaa,b), A. Gadea,b), M. Horoid), S. Kannoe), K. Kemperk), T. Motobayashic), A. Obertellia), T. Otsukaa,c,h), L. A. Rileyf), H. Sagawag), H. Sakuraic), K. Starostaa,b), H. Suzukih), S. Takeuchic), J. R. Terrya,b), J. Tostevini), Y. Utsunoij), D. Weisshaara), K. Yonedac), H. Zwahlena,b) a) National Superconducting Cyclotron Laboratory, Michigan State University b) Department of Physics and Astronomy, Michigan State University c) RIKEN Nishina Center for Accelerator-Based Science d) Physics Department, Central Michigan University e) Department of Physics, Rikkyo University f) Department of Physics and Astronomy, Ursinus College g) Center for Mathematical Sciences, University of Aizu h) Department of Physics, University of Tokyo i) Department of Physics, University of Surrey j) Japan Atomic Energy Research Institute k) Physics Department, Florida State University

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